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Detailed explanation of the four scopes in JavaBean

黄舟

Oct 13, 2017 am 10:38 AM

javabeanScopescope

This article mainly introduces the relevant information on the detailed explanation of the four scopes of JavaBean. I hope this article can help everyone. Friends in need can refer to the following

The four scopes of JavaBean Detailed explanation

One explanation

The scope attribute of useBeans can be used to specify the scope of javabean.

Two or four scopes

Three codes

1.login.jsp

<%@ page language="java" import="java.util.*" contentType="text/html; charset=utf-8" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
 <head>
  <base href="<%=basePath%>" rel="external nofollow" rel="external nofollow" rel="external nofollow" >
  
  <title>My JSP &#39;login.jsp&#39; starting page</title>
  
    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">  
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
    <!--
    <link rel="stylesheet" type="text/css" href="styles.css" rel="external nofollow" rel="external nofollow" rel="external nofollow" >
    -->
 
 </head>
 
 <body>
  <h1 id="系统登录">系统登录</h1>
  <hr>
  <form name="loginForm" action="dologin.jsp?mypass=999999" method="post">
   <table>
    <tr>
     <td>用户名：</td>
     <td><input type="text" name="username" value=""/></td>
    </tr>
    <tr>
     <td>密码：</td>
     <td><input type="password" name="password" value=""/></td>
    </tr>
    <tr>
     <td colspan="2" align="center"><input type="submit" value="登录"/></td>
     
    </tr>
   </table>
  </form>
 </body>
</html>

2.dologin.jsp

<%@ page language="java" import="java.util.*" contentType="text/html; charset=utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
 <head>
  <base href="<%=basePath%>" rel="external nofollow" rel="external nofollow" rel="external nofollow" >
  
  <title>My JSP &#39;dologin.jsp&#39; starting page</title>
  
    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">  
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
    <!--
    <link rel="stylesheet" type="text/css" href="styles.css" rel="external nofollow" rel="external nofollow" rel="external nofollow" >
    -->
 
 </head>
 
 <body>
  <jsp:useBean id="myUsers" class="com.po.Users" scope="page"/>
  <h1 id="setProperty动作元素">setProperty动作元素</h1>
  <hr>
  <!--根据表单自动匹配所有的属性 -->
  <%--
  <jsp:setProperty name="myUsers" property="*"/> 
  --%>
  <!--根据表单匹配所有部分的属性 -->
  <%--
  <jsp:setProperty name="myUsers" property="username"/> 
  --%>
  <!--根表单无关，通过手工赋值给属性 -->
  <%--
  <jsp:setProperty name="myUsers" property="username" value="lisi"/>
  <jsp:setProperty name="myUsers" property="password" value="888888"/>
  --%>
  <!--通过URL传参数给属性赋值 -->
  <jsp:setProperty name="myUsers" property="username"/>
  <jsp:setProperty name="myUsers" property="password" param="mypass"/>
  <!-- 使用传统的表达式方式来获取用户名和密码 -->
  <%--  
    用户名：<%=myUsers.getUsername() %><br>
    密码：<%=myUsers.getPassword() %><br>
  --%>
  <!-- 使用getProperty方式来获取用户名和密码 -->
   用户名：<jsp:getProperty name="myUsers" property="username"/> <br>
   密码：<jsp:getProperty name="myUsers" property="password"/><br>
  <br>
  <br>
 
   <a href="testScope.jsp" rel="external nofollow" >测试javabean的四个作用域范围</a>
 
   <%
     request.getRequestDispatcher("testScope.jsp").forward(request, response);
   %>
 
 </body>
</html>

3. testScope.jsp

<%@ page language="java" import="java.util.*"
    contentType="text/html; charset=utf-8"%>
<%@ page import="com.po.Users"%>
<%
    String path = request.getContextPath();
    String basePath = request.getScheme() + "://"
            + request.getServerName() + ":" + request.getServerPort()
            + path + "/";
%>
 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>" rel="external nofollow" rel="external nofollow" rel="external nofollow" >
 
<title>My JSP &#39;testScope.jsp&#39; starting page</title>
 
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
    <link rel="stylesheet" type="text/css" href="styles.css" rel="external nofollow" rel="external nofollow" rel="external nofollow" >
    -->
 
</head>
 
<body>
    <h1 id="Javabean的四个作用域范围">Javabean的四个作用域范围</h1>
    <hr>
    <jsp:useBean id="myUsers" class="com.po.Users" scope="page" />
    用户名：<jsp:getProperty name="myUsers" property="username" /><br> 密码：<jsp:getProperty
        name="myUsers" property="password" /><br>
    <!-- 使用内置对象获取用户名和密码 -->
    <hr>
    <%--
    用户名：<%=((Users)application.getAttribute("myUsers")).getUsername()%><br>
    密码：<%=((Users)application.getAttribute("myUsers")).getPassword() %><br>
  --%>
    <%--
    用户名：<%=((Users)session.getAttribute("myUsers")).getUsername()%><br>
    密码：<%=((Users)session.getAttribute("myUsers")).getPassword() %><br>
  --%>
    <%--
    用户名：<%=((Users)request.getAttribute("myUsers")).getUsername()%><br>
    密码：<%=((Users)request.getAttribute("myUsers")).getPassword() %><br>
  --%>
    <%
        String username = "";
        String password = "";
        if (pageContext.getAttribute("myUsers") != null) {
            username = ((Users) pageContext.getAttribute("myUsers"))
                    .getUsername();
            password = ((Users) pageContext.getAttribute("myUsers"))
                    .getPassword();
        }
    %>
 
    用户名：<%=username%><br> 密码：<%=password%><br>
 
 
 
</body>
</html>

Four test results

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