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Heim  >  Artikel  >  Backend-Entwicklung  >  Wie Session verhindert, dass Formulare wiederholt gesendet werden

Wie Session verhindert, dass Formulare wiederholt gesendet werden

零到壹度
零到壹度Original
2018-03-28 13:13:241846Durchsuche

Dieser Artikel zeigt Ihnen hauptsächlich, wie Sie die wiederholte Einreichung von Formularen in der Sitzung verhindern können. Er hat einen guten Referenzwert und ich hoffe, dass er für alle hilfreich sein wird. Folgen wir dem Herausgeber und werfen wir einen Blick darauf.

Wenn in der normalen Entwicklung die Netzwerkgeschwindigkeit relativ langsam ist und der Benutzer das Formular sendet und feststellt, dass der Server einen halben Tag lang nicht geantwortet hat, denkt der Benutzer möglicherweise, dass er das Formular nicht gesendet hat und klicken Sie erneut auf die Schaltfläche „Senden“, um das Formular wiederholt zu senden. Wir müssen verhindern, dass das Formular während der Entwicklung wiederholt gesendet wird.

1. Häufige Anwendungsszenarien für die wiederholte Formularübermittlung

Es gibt die folgende form.jsp-Seite

<code style="border-radius: 4px;font-size: 0.85em;margin: 0px 0.15em;background: rgb(40, 44, 52);color: rgb(171, 178, 191);display: block;padding: 7.5px;overflow-x: auto;white-space: nowrap;" class="hljs-default">1 <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 561px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">%@</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">page</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 66px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">language</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"java"</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">import</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 108px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"java.util.*"</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 100px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">pageEncoding</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"UTF-8"</span>%></span><br> 2 <span class="hljs-default-meta" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 124px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;"><!DOCTYPE HTML></span><br> 3 <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">html</span>></span><br> 4   <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">head</span>></span><br> 5     <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">title</span>></span>Form表单<span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 65px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"></<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">title</span>></span><br> 6   <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"></<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">head</span>></span><br> 7   <br> 8   <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">body</span>></span><br> 9       <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 710px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">form</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">action</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 479px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"${pageContext.request.contextPath}/servlet/DoFormServlet"</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">method</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"post"</span>></span><br>10         用户名：<span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 289px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">input</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">type</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"text"</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">name</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 83px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"username"</span>></span><br>11         <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 376px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">input</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">type</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 65px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"submit"</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">value</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 48px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"提交"</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">id</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 66px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"submit"</span>></span><br>12     <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"></<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">form</span>></span><br>13   <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"></<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">body</span>></span><br>14 <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"></<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">html</span>></span></code>

Das Formular wird an gesendet DoFormServlet zur Verarbeitung 

<code style="border-radius: 4px;font-size: 0.85em;margin: 0px 0.15em;background: rgb(40, 44, 52);color: rgb(171, 178, 191);display: block;padding: 7.5px;overflow-x: auto;white-space: nowrap;" class="hljs-default"><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 8px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">1</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">package</span> xdp.gacl.session;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">2</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">3</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> java.io.IOException;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">4</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> javax.servlet.ServletException;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">5</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> javax.servlet.http.HttpServlet;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">6</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> javax.servlet.http.HttpServletRequest;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">7</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> javax.servlet.http.HttpServletResponse;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">8</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">9</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">public</span> <span class="hljs-default-class" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 330px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">class</span> <span class="hljs-default-title" style="color: rgb(230, 192, 123);background: rgba(0, 0, 0, 0);display: inline;width: 108px;text-decoration: none solid rgb(230, 192, 123);font-weight: 400;font-style: normal;">DoFormServlet</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">extends</span> <span class="hljs-default-title" style="color: rgb(230, 192, 123);background: rgba(0, 0, 0, 0);display: inline;width: 91px;text-decoration: none solid rgb(230, 192, 123);font-weight: 400;font-style: normal;">HttpServlet</span> </span>{<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">10</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">11</span>     <span class="hljs-default-function" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 676px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">public</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">void</span> <span class="hljs-default-title" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;">doGet</span><span class="hljs-default-params" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 479px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;">(HttpServletRequest request, HttpServletResponse response)</span><br>12             <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">throws</span> ServletException, IOException </span>{<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">13</span>         <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 865px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//客户端是以UTF-8编码传输数据到服务器端的，所以需要设置服务器端以UTF-8的编码进行接收，否则对于中文数据就会产生乱码</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">14</span>         request.setCharacterEncoding(<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"UTF-8"</span>);<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">15</span>         String userName = request.getParameter(<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 83px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"username"</span>);<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">16</span>         <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 25px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">try</span> {<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">17</span>             <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 460px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//让当前的线程睡眠3秒钟，模拟网络延迟而导致表单重复提交的现象</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">18</span>             Thread.sleep(<span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 8px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">3</span>*<span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">1000</span>);<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">19</span>         } <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">catch</span> (InterruptedException e) {<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">20</span>             e.printStackTrace();<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">21</span>         }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">22</span>         System.out.println(<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 166px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"向数据库中插入数据："</span>+userName);<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">23</span>     }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">24</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">25</span>     <span class="hljs-default-function" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 685px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">public</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">void</span> <span class="hljs-default-title" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;">doPost</span><span class="hljs-default-params" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 478px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;">(HttpServletRequest request, HttpServletResponse response)</span><br>26             <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">throws</span> ServletException, IOException </span>{<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">27</span>         doGet(request, response);<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">28</span>     }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">29</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">30</span> }</code>

Wenn das Formular nicht wiederholt übermittelt wird, führen die folgenden Vorgänge dazu, dass das Formular aufgrund von Netzwerkverzögerungen mehrmals übermittelt wird

1.1. Szenario 1: Im Falle einer Netzwerkverzögerung führt die Tatsache, dass Benutzer mehrmals auf die Schaltfläche „Senden“ klicken können, dazu, dass das Formular wiederholt gesendet wird

Die Demonstrationsanimation sieht wie folgt aus:

Wie Session verhindert, dass Formulare wiederholt gesendet werden

1.2. Nachdem das Formular gesendet wurde, klickt der Benutzer auf die Schaltfläche [Aktualisieren], wodurch das Formular wiederholt gesendet wird.

Die Demonstrationsanimation ist wie folgt folgt:

Wie Session verhindert, dass Formulare wiederholt gesendet werden

Wenn Sie auf die Schaltfläche „Aktualisieren“ des Browsers klicken, wird das gleiche getan, was der Browser beim letzten Mal getan hat, da dies auch dazu führt, dass das Formular wiederholt gesendet wird.

1.3. Szenario 3: Nachdem der Benutzer das Formular abgeschickt hat, klicken Sie auf die Schaltfläche [Zurück] des Browsers, um zur Formularseite zurückzukehren und erneut abzusenden

Die Demonstrationsanimation sieht wie folgt aus:

Wie Session verhindert, dass Formulare wiederholt gesendet werden

2. Verwenden Sie JavaScript, um das wiederholte Senden von Formularen zu verhindern

Da das oben erwähnte Problem der wiederholten Formularübermittlung besteht, müssen wir einen Weg finden, es zu lösen Eine gebräuchlichere Methode ist die Verwendung von JavaScript. Um zu verhindern, dass das Formular wiederholt gesendet wird, lautet die spezifische Methode wie folgt:

Ändern Sie die Seite form.jsp und fügen Sie den folgenden JavaScript-Code hinzu, um zu verhindern, dass das Formular wiederholt gesendet wird

<code style="border-radius: 4px;font-size: 0.85em;margin: 0px 0.15em;background: rgb(40, 44, 52);color: rgb(171, 178, 191);display: block;padding: 7.5px;overflow-x: auto;white-space: nowrap;" class="hljs-default">1 <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 561px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">%@</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">page</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 66px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">language</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"java"</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">import</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 108px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"java.util.*"</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 100px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">pageEncoding</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"UTF-8"</span>%></span><br> 2 <span class="hljs-default-meta" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 124px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;"><!DOCTYPE HTML></span><br> 3 <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">html</span>></span><br> 4   <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">head</span>></span><br> 5     <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">title</span>></span>Form表单<span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 65px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"></<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">title</span>></span><br> 6         <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 256px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">script</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">type</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 140px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"text/javascript"</span>></span><span class="javascript"><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">7</span>         <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 25px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">var</span> isCommitted = <span class="hljs-default-literal" style="color: rgb(86, 182, 194);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(86, 182, 194);font-weight: 400;font-style: normal;">false</span>;<span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 268px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//表单是否已经提交标识，默认为false</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">8</span>         <span class="hljs-default-function" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 158px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 66px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">function</span> <span class="hljs-default-title" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 66px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;">dosubmit</span>(<span class="hljs-default-params" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 0px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"></span>)</span>{<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">9</span>             <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">if</span>(isCommitted==<span class="hljs-default-literal" style="color: rgb(86, 182, 194);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(86, 182, 194);font-weight: 400;font-style: normal;">false</span>){<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">10</span>                 isCommitted = <span class="hljs-default-literal" style="color: rgb(86, 182, 194);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(86, 182, 194);font-weight: 400;font-style: normal;">true</span>;<span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 350px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//提交表单后，将表单是否已经提交标识设置为true</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">11</span>                 <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">return</span> <span class="hljs-default-literal" style="color: rgb(86, 182, 194);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(86, 182, 194);font-weight: 400;font-style: normal;">true</span>;<span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 185px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//返回true让表单正常提交</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">12</span>             }<span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">else</span>{<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">13</span>                 <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">return</span> <span class="hljs-default-literal" style="color: rgb(86, 182, 194);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(86, 182, 194);font-weight: 400;font-style: normal;">false</span>;<span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 208px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//返回false那么表单将不提交</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">14</span>             }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">15</span>         }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">16</span>     </span><span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 74px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"></<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">script</span>></span><br>17   <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"></<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">head</span>></span><br>18   <br>19   <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">body</span>></span><br>20       <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 949px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">form</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">action</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 479px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"${pageContext.request.contextPath}/servlet/DoFormServlet"</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 66px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">onsubmit</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 156px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"return dosubmit()"</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">method</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"post"</span>></span><br>21         用户名：<span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 289px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">input</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">type</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"text"</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">name</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 83px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"username"</span>></span><br>22         <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 376px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">input</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">type</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 65px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"submit"</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">value</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 48px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"提交"</span> <span class="hljs-default-attr" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">id</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 66px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"submit"</span>></span><br>23     <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"></<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">form</span>></span><br>24   <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"></<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">body</span>></span><br>25 <span class="hljs-default-tag" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"></<span class="hljs-default-name" style="color: rgb(224, 108, 117);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(224, 108, 117);font-weight: 400;font-style: normal;">html</span>></span></code>

Werfen wir einen Blick darauf, dass JavaScript verwendet wird, um wiederholte Formularübermittlungen zu verhindern. Der laufende Effekt ist wie folgt:

Wie Session verhindert, dass Formulare wiederholt gesendet werden

Sie kann sehen, dass „ den Benutzern bei Netzwerkverzögerungen Zeit lässt. Durch mehrmaliges Klicken auf die Schaltfläche „Senden“ wird das Formular wiederholt gesendet“In diesem Anwendungsszenario kann JavaScript verwendet werden, um dieses Problem zu lösen. Die Lösung ist"Verwenden Sie JavaScript, um zu steuern, dass das Formular nur einmal übermittelt werden soll".

Zusätzlich zu dieser Methode besteht eine weitere gängige Methode darin, die Schaltfläche „Senden“ so festzulegen, dass sie nach dem Absenden des Formulars nicht mehr verfügbar ist, sodass der Benutzer nicht die Möglichkeit hat, ein zweites Mal auf die Schaltfläche „Senden“ zu klicken Der Code lautet wie folgt: 

<code style="border-radius: 4px;font-size: 0.85em;margin: 0px 0.15em;background: rgb(40, 44, 52);color: rgb(171, 178, 191);display: block;padding: 7.5px;overflow-x: auto;white-space: nowrap;" class="hljs-default"><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 8px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">1</span> <span class="hljs-default-function" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 156px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 66px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">function</span> <span class="hljs-default-title" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 66px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;">dosubmit</span>(<span class="hljs-default-params" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 0px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"></span>)</span>{<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 8px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">2</span>     <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 138px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//获取表单提交按钮</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 8px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">3</span>     <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 25px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">var</span> btnSubmit = <span class="hljs-default-built_in" style="color: rgb(230, 192, 123);background: rgba(0, 0, 0, 0);display: inline;width: 66px;text-decoration: none solid rgb(230, 192, 123);font-weight: 400;font-style: normal;">document</span>.getElementById(<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 66px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"submit"</span>);<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 8px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">4</span>     <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 483px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//将表单提交按钮设置为不可用，这样就可以避免用户再次点击提交按钮</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 8px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">5</span>     btnSubmit.disabled= <span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 83px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"disabled"</span>;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 8px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">6</span>     <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 215px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//返回true让表单可以正常提交</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 8px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">7</span>     <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">return</span> <span class="hljs-default-literal" style="color: rgb(86, 182, 194);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(86, 182, 194);font-weight: 400;font-style: normal;">true</span>;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 8px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">8</span> }</code>

Der Operationseffekt ist wie folgt:

Wie Session verhindert, dass Formulare wiederholt gesendet werden

 　　另外还有一种做法就是提交表单后，将提交按钮隐藏起来，这种做法和将提交按钮设置为不可用是差不多的，个人觉得将提交按钮隐藏影响到页面布局的美观，并且可能会让用户误以为是bug(怎么我一点击按钮，按钮就不见了呢？用户可能会有这样的疑问)，我个人在开发中用得比较多的是表单提交后，将提交按钮设置为不可用，反正使用JavaScript防止表单重复提交的做法都是差不多的，目的都是让表单只能提交一次，这样就可以做到表单不重复提交了。

　　使用JavaScript防止表单重复提交的做法只对上述提交到导致表单重复提交的三种场景中的【场景一】有效，而对于【场景二】和【场景三】是没有用，依然无法解决表单重复提交问题。

三、利用Session防止表单重复提交

　　对于【场景二】和【场景三】导致表单重复提交的问题，既然客户端无法解决，那么就在服务器端解决，在服务器端解决就需要用到session了。

　　具体的做法：在服务器端生成一个唯一的随机标识号，专业术语称为Token(令牌)，同时在当前用户的Session域中保存这个Token。然后将Token发送到客户端的Form表单中，在Form表单中使用隐藏域来存储这个Token，表单提交的时候连同这个Token一起提交到服务器端，然后在服务器端判断客户端提交上来的Token与服务器端生成的Token是否一致，如果不一致，那就是重复提交了，此时服务器端就可以不处理重复提交的表单。如果相同则处理表单提交，处理完后清除当前用户的Session域中存储的标识号。
　　在下列情况下，服务器程序将拒绝处理用户提交的表单请求：

  1. 存储Session域中的Token(令牌)与表单提交的Token(令牌)不同。

  2. 当前用户的Session中不存在Token(令牌)。

  3. 用户提交的表单数据中没有Token(令牌)。

看具体的范例：

　　1.创建FormServlet，用于生成Token(令牌)和跳转到form.jsp页面

<code style="border-radius: 4px;font-size: 0.85em;margin: 0px 0.15em;background: rgb(40, 44, 52);color: rgb(171, 178, 191);display: block;padding: 7.5px;overflow-x: auto;white-space: nowrap;" class="hljs-default"><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 8px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">1</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">package</span> xdp.gacl.session;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">2</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">3</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> java.io.IOException;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">4</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> javax.servlet.ServletException;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">5</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> javax.servlet.http.HttpServlet;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">6</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> javax.servlet.http.HttpServletRequest;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">7</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> javax.servlet.http.HttpServletResponse;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">8</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">9</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">public</span> <span class="hljs-default-class" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 313px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">class</span> <span class="hljs-default-title" style="color: rgb(230, 192, 123);background: rgba(0, 0, 0, 0);display: inline;width: 91px;text-decoration: none solid rgb(230, 192, 123);font-weight: 400;font-style: normal;">FormServlet</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 59px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">extends</span> <span class="hljs-default-title" style="color: rgb(230, 192, 123);background: rgba(0, 0, 0, 0);display: inline;width: 91px;text-decoration: none solid rgb(230, 192, 123);font-weight: 400;font-style: normal;">HttpServlet</span> </span>{<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">10</span>     <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">private</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">static</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">final</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">long</span> serialVersionUID = -<span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 158px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">884689940866074733L</span>;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">11</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">12</span>     <span class="hljs-default-function" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 676px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">public</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">void</span> <span class="hljs-default-title" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;">doGet</span><span class="hljs-default-params" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 479px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;">(HttpServletRequest request, HttpServletResponse response)</span><br>13             <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">throws</span> ServletException, IOException </span>{<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">14</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">15</span>         String token = TokenProccessor.getInstance().makeToken();<span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 78px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//创建令牌</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">16</span>         System.out.println(<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 238px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"在FormServlet中生成的token："</span>+token);<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">17</span>         request.getSession().setAttribute(<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"token"</span>, token);  <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 283px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//在服务器使用session保存token(令牌)</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">18</span>         request.getRequestDispatcher(<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 90px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"/form.jsp"</span>).forward(request, response);<span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 158px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//跳转到form.jsp页面</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">19</span>     }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">20</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">21</span>     <span class="hljs-default-function" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 685px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">public</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">void</span> <span class="hljs-default-title" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;">doPost</span><span class="hljs-default-params" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 478px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;">(HttpServletRequest request, HttpServletResponse response)</span><br>22             <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">throws</span> ServletException, IOException </span>{<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">23</span>         doGet(request, response);<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">24</span>     }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">25</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">26</span> }</code>

　　2.在form.jsp中使用隐藏域来存储Token(令牌)

<code style="border-radius: 4px;font-size: 0.85em;margin: 0px 0.15em;background: rgb(40, 44, 52);color: rgb(171, 178, 191);display: block;padding: 7.5px;overflow-x: auto;white-space: nowrap;" class="hljs-default"><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 8px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">1</span> <%@ page <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 66px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">language</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"java"</span> import=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 108px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"java.util.*"</span> pageEncoding=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"UTF-8"</span>%><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">2</span> <!DOCTYPE HTML PUBLIC <span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 330px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"-//W3C//DTD HTML 4.01 Transitional//EN"</span>><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">3</span> <span class="hljs-default-symbol" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;"><html></span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">4</span> <span class="hljs-default-symbol" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;"><head></span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">5</span> <span class="hljs-default-symbol" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;"><title></span>form表单</title><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">6</span> </head><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">7</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">8</span> <span class="hljs-default-symbol" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;"><body></span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">9</span>     <form action=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 478px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"${pageContext.request.contextPath}/servlet/DoFormServlet"</span> method=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"post"</span>><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">10</span>         <%--使用隐藏域存储生成的token--%><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">11</span>         <%--<br/><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">12</span>             <<span class="hljs-default-built_in" style="color: rgb(230, 192, 123);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(230, 192, 123);font-weight: 400;font-style: normal;">input</span> <span class="hljs-default-built_in" style="color: rgb(230, 192, 123);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(230, 192, 123);font-weight: 400;font-style: normal;">type</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 66px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"hidden"</span> name=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"token"</span> value=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 214px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"<%=session.getAttribute("</span>token<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">") %>"><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">13</span>         --%><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">14</span>         <%--使用EL表达式取出存储在session中的token--%><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">15</span>         <<span class="hljs-default-built_in" style="color: rgb(230, 192, 123);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(230, 192, 123);font-weight: 400;font-style: normal;">input</span> <span class="hljs-default-built_in" style="color: rgb(230, 192, 123);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(230, 192, 123);font-weight: 400;font-style: normal;">type</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 65px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"hidden"</span> name=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"token"</span> value=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 83px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"${token}"</span>/> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">16</span>         用户名：<<span class="hljs-default-built_in" style="color: rgb(230, 192, 123);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(230, 192, 123);font-weight: 400;font-style: normal;">input</span> <span class="hljs-default-built_in" style="color: rgb(230, 192, 123);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(230, 192, 123);font-weight: 400;font-style: normal;">type</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"text"</span> name=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 83px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"username"</span>> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">17</span>         <<span class="hljs-default-built_in" style="color: rgb(230, 192, 123);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(230, 192, 123);font-weight: 400;font-style: normal;">input</span> <span class="hljs-default-built_in" style="color: rgb(230, 192, 123);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(230, 192, 123);font-weight: 400;font-style: normal;">type</span>=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 65px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"submit"</span> value=<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 48px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"提交"</span>><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">18</span>     </form><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">19</span> </body><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">20</span> </html></code>

　　3.DoFormServlet处理表单提交

<code style="border-radius: 4px;font-size: 0.85em;margin: 0px 0.15em;background: rgb(40, 44, 52);color: rgb(171, 178, 191);display: block;padding: 7.5px;overflow-x: auto;white-space: nowrap;" class="hljs-default"><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 8px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">1</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">package</span> xdp.gacl.session;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">2</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">3</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> java.io.IOException;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">4</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> javax.servlet.ServletException;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">5</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> javax.servlet.http.HttpServlet;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">6</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> javax.servlet.http.HttpServletRequest;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">7</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> javax.servlet.http.HttpServletResponse;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">8</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">9</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">public</span> <span class="hljs-default-class" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 330px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">class</span> <span class="hljs-default-title" style="color: rgb(230, 192, 123);background: rgba(0, 0, 0, 0);display: inline;width: 108px;text-decoration: none solid rgb(230, 192, 123);font-weight: 400;font-style: normal;">DoFormServlet</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">extends</span> <span class="hljs-default-title" style="color: rgb(230, 192, 123);background: rgba(0, 0, 0, 0);display: inline;width: 91px;text-decoration: none solid rgb(230, 192, 123);font-weight: 400;font-style: normal;">HttpServlet</span> </span>{<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">10</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">11</span>     <span class="hljs-default-function" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 676px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">public</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">void</span> <span class="hljs-default-title" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;">doGet</span><span class="hljs-default-params" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 479px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;">(HttpServletRequest request, HttpServletResponse response)</span><br>12                 <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">throws</span> ServletException, IOException </span>{<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">13</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">14</span>             <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">boolean</span> b = isRepeatSubmit(request);<span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 181px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//判断用户是否是重复提交</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">15</span>             <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">if</span>(b==<span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">true</span>){<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">16</span>                 System.out.println(<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 121px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"请不要重复提交"</span>);<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">17</span>                 <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">return</span>;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">18</span>             }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">19</span>             request.getSession().removeAttribute(<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"token"</span>);<span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 176px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//移除session中的token</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">20</span>             System.out.println(<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 166px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"处理用户提交请求！！"</span>);<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">21</span>         }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">22</span>         <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">23</span>         <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 506px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">/**<br>24          * 判断客户端提交上来的令牌和服务器端生成的令牌是否一致<br>25          * <span class="hljs-default-doctag" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: italic;">@param</span> request<br>26          * <span class="hljs-default-doctag" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: italic;">@return</span> <br>27          *         true 用户重复提交了表单 <br>28          *         false 用户没有重复提交表单<br>29          */</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">30</span>         <span class="hljs-default-function" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 488px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 59px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">private</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">boolean</span> <span class="hljs-default-title" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 115px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;">isRepeatSubmit</span><span class="hljs-default-params" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 231px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;">(HttpServletRequest request)</span> </span>{<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">31</span>             String client_token = request.getParameter(<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 59px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"token"</span>);<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">32</span>             <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 471px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//1、如果用户提交的表单数据中没有token，则用户是重复提交了表单</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">33</span>             <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">if</span>(client_token==<span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">null</span>){<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">34</span>                 <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">return</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">true</span>;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">35</span>             }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">36</span>             <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 220px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//取出存储在Session中的token</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">37</span>             String server_token = (String) request.getSession().getAttribute(<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"token"</span>);<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">38</span>             <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 530px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//2、如果当前用户的Session中不存在Token(令牌)，则用户是重复提交了表单</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">39</span>             <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">if</span>(server_token==<span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">null</span>){<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">40</span>                 <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">return</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">true</span>;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">41</span>             }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">42</span>             <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 648px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//3、存储在Session中的Token(令牌)与表单提交的Token(令牌)不同，则用户是重复提交了表单</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">43</span>             <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">if</span>(!client_token.equals(server_token)){<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">44</span>                 <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">return</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">true</span>;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">45</span>             }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">46</span>             <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">47</span>             <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">return</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">false</span>;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">48</span>         }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">49</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">50</span>     <span class="hljs-default-function" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 685px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">public</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 34px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">void</span> <span class="hljs-default-title" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;">doPost</span><span class="hljs-default-params" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 478px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;">(HttpServletRequest request, HttpServletResponse response)</span><br>51             <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">throws</span> ServletException, IOException </span>{<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">52</span>         doGet(request, response);<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">53</span>     }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">54</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">55</span> }</code>

　　生成Token的工具类TokenProccessor

<code style="border-radius: 4px;font-size: 0.85em;margin: 0px 0.15em;background: rgb(40, 44, 52);color: rgb(171, 178, 191);display: block;padding: 7.5px;overflow-x: auto;white-space: nowrap;" class="hljs-default"><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 8px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">1</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">package</span> xdp.gacl.session;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">2</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">3</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> java.security.MessageDigest;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">4</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> java.security.NoSuchAlgorithmException;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">5</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> java.util.Random;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">6</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">import</span> sun.misc.BASE64Encoder;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">7</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">8</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">public</span> <span class="hljs-default-class" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 181px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">class</span> <span class="hljs-default-title" style="color: rgb(230, 192, 123);background: rgba(0, 0, 0, 0);display: inline;width: 124px;text-decoration: none solid rgb(230, 192, 123);font-weight: 400;font-style: normal;">TokenProccessor</span> </span>{<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 9px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">9</span> <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">10</span>     <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 404px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">/*<br>11      *单例设计模式（保证类的对象在内存中只有一个）<br>12      *1、把类的构造函数私有<br>13      *2、自己创建一个类的对象<br>14      *3、对外提供一个公共的方法，返回类的对象<br>15      */</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">16</span>     <span class="hljs-default-function" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 206px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">private</span> <span class="hljs-default-title" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 124px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;">TokenProccessor</span><span class="hljs-default-params" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;">()</span></span>{}<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">17</span>     <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">18</span>     <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">private</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">static</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">final</span> TokenProccessor instance = <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 24px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">new</span> TokenProccessor();<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">19</span>     <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">20</span>     <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 173px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">/**<br>21      * 返回类的对象<br>22      * <span class="hljs-default-doctag" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: italic;">@return</span><br>23      */</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">24</span>     <span class="hljs-default-function" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 355px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">public</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">static</span> TokenProccessor <span class="hljs-default-title" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 90px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;">getInstance</span><span class="hljs-default-params" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 18px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;">()</span></span>{<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">25</span>         <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">return</span> instance;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">26</span>     }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">27</span>     <br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">28</span>     <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 336px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">/**<br>29      * 生成Token<br>30      * Token：Nv6RRuGEVvmGjB+jimI/gw==<br>31      * <span class="hljs-default-doctag" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 58px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: italic;">@return</span><br>32      */</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">33</span>     <span class="hljs-default-function" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 206px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;"><span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 50px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">public</span> String <span class="hljs-default-title" style="color: rgb(97, 174, 238);background: rgba(0, 0, 0, 0);display: inline;width: 75px;text-decoration: none solid rgb(97, 174, 238);font-weight: 400;font-style: normal;">makeToken</span><span class="hljs-default-params" style="color: rgb(171, 178, 191);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(171, 178, 191);font-weight: 400;font-style: normal;">()</span></span>{  <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 131px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//checkException</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">34</span>         <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 396px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//  7346734837483  834u938493493849384  43434384</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">35</span>         String token = (System.currentTimeMillis() + <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 25px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">new</span> Random().nextInt(<span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 74px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">999999999</span>)) + <span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">""</span>;<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">36</span>         <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 284px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//数据指纹   128位长   16个字节  md5</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">37</span>         <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 25px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">try</span> {<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">38</span>             MessageDigest md = MessageDigest.getInstance(<span class="hljs-default-string" style="color: rgb(152, 195, 121);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(152, 195, 121);font-weight: 400;font-style: normal;">"md5"</span>);<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">39</span>             <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 33px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">byte</span> md5[] =  md.digest(token.getBytes());<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">40</span>             <span class="hljs-default-comment" style="color: rgb(92, 99, 112);background: rgba(0, 0, 0, 0);display: inline;width: 393px;text-decoration: none solid rgb(92, 99, 112);font-weight: 400;font-style: italic;">//base64编码--任意二进制编码明文字符   adfsdfsdfsf</span><br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">41</span>             BASE64Encoder encoder = <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 25px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">new</span> BASE64Encoder();<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">42</span>             <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 49px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">return</span> encoder.encode(md5);<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">43</span>         } <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">catch</span> (NoSuchAlgorithmException e) {<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">44</span>             <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 41px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">throw</span> <span class="hljs-default-keyword" style="color: rgb(198, 120, 221);background: rgba(0, 0, 0, 0);display: inline;width: 25px;text-decoration: none solid rgb(198, 120, 221);font-weight: 400;font-style: normal;">new</span> RuntimeException(e);<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">45</span>         }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">46</span>     }<br><span class="hljs-default-number" style="color: rgb(209, 154, 102);background: rgba(0, 0, 0, 0);display: inline;width: 16px;text-decoration: none solid rgb(209, 154, 102);font-weight: 400;font-style: normal;">47</span> }</code>

　　首先访问FormServlet，在FormServlet中生成Token之后再重定向到form.jsp页面，这次是在服务器端处理表单重复提交的，运行效果如下：

Wie Session verhindert, dass Formulare wiederholt gesendet werden

　　从运行效果中可以看到，通过这种方式处理表单重复提交，可以解决上述的场景二和场景三中出现的表单重复提交问题。

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