php防止重复提交问题总结
用户提交表单时可能因为网速的原因,或者网页被恶意刷新,致使同一条记录重复插入到数据库中,这是一个比较棘手的问题。我们可以从客户端和服务器端一起着手,设法避免同一表单的重复提交。
1.使用客户端脚本
提到客户端脚本,经常使用的是JavaScript进行常规输入验证。在下面的例子中,我们使用它处理表单的重复提交问题,请看下面的代码:
当用户单击“提交”按钮后,该按钮将变为灰色不可用状态,如图5-6所示。
上面的例子中使用OnClick事件检测用户的提交状态,如果单击了“提交”按钮,该按钮立即置为失效状态,用户不能单击按钮再次提交。
还有一个方法,也是利用JavaScript的功能,但是使用的是OnSubmit()方法,如果已经提交过一次表单,将立即弹出对话框,代码如下:
在上例中,如果用户已经单击“提交”按钮,该脚本会自动记录当前的状态,并将submitcount变量自加1,当用户试图再次提交时,脚本判断submitcount变量值非零,提示用户已经提交,从而避免重复提交表单。
2.使用Cookie处理
使用Cookie记录表单提交的状态,根据其状态可以检查是否已经提交表单,请见下面的代码:
if(isset($_POST['go'])){
setcookie("tempcookie","",time()+30);
header("Location:".$_SERVER[PHP_SELF]);
exit();
}
if(isset($_COOKIE["tempcookie"])){
setcookie("tempcookie","",0);
echo "您已经提交过表单";
}
?>
如果客户端禁止了Cookie,该方法将不起任何作用,这点请注意。关于Cookie的详细介绍,请参阅第10章“PHP会话管理”。
3.使用Session处理
利用PHP的Session功能,也能避免重复提交表单。Session保存在服务器端,在PHP运行过程中可以改变Session变量,下次访问这个变量时,得到的是新赋的值,所以,可以用一个Session变量记录表单提交的值,如果不匹配,则认为是用户在重复提交,请见如下代码:
session_start();
//根据当前SESSION生成随机数
$code = mt_rand(0,1000000);
$_SESSION['code'] = $code;
?>
在页面表单上将随机数作为隐藏值进行传递,代码如下:
在接收页面的PHP代码如下:
session_start();
if(isset($_POST['originator'])) {
if($_POST['originator'] == $_SESSION['code']){
// 处理该表单的语句,省略
}else{
echo ‘请不要刷新本页面或重复提交表单!’;
}
}
?>
关于Session的内容,我们会在第10章“PHP会话管理”详细讨论,你可以直接查阅这一章,然后再返回本节继续阅读。
4.使用header函数转向
除了上面的方法之外,还有一个更简单的方法,那就是当用户提交表单,服务器端处理后立即转向其他的页面,代码如下所示。
if (isset($_POST['action']) && $_POST['action'] == 'submitted') {
//处理数据,如插入数据后,立即转向到其他页面
header('location:submits_success.php');
}
这样,即使用户使用刷新键,也不会导致表单的重复提交,因为已经转向新的页面,而这个页面脚本已经不理会任何提交的数据了。
5.8.4 表单过期的处理
在开发过程中,经常会出现表单出错而返回页面的时候填写的信息全部丢失的情况,为了支持页面回跳,可以通过以下两种方法实现。
1.使用header头设置缓存控制头Cache-control。
header('Cache-control: private, must-revalidate'); //支持页面回跳
2.使用session_cache_limiter方法。
session_cache_limiter('private, must-revalidate'); //要写在session_start方法之前
下面的代码片断可以防止用户填写表单的时候,单击“提交”按钮返回时,刚刚在表单上填写的内容不会被清除:
session_cache_limiter('nocache');
session_cache_limiter('private');
session_cache_limiter('public');
session_start();
//以下是表单内容,这样在用户返回该表单时,已经填写的内容不会被清空
将该段代码贴到所要应用的脚本顶部即可。
Cache-Control消息头域说明
Cache-Control指定请求和响应遵循的缓存机制。在请求消息或响应消息中设置Cache-Control并不会修改另一个消息处理过程中的缓存处理过程。
请求时的缓存指令包括no-cache、no-store、max-age、max-stale、min-fresh和only-if- cached,响应消息中的指令包括public、private、no-cache、no-store、no-transform、must- revalidate、proxy-revalidate和max-age。各个消息中的指令含义如表5-3所示。
缓存指令
说 明
public
指示响应可被任何缓存区缓存
private
指示对于单个用户的整个或部分响应消息,不能被共享缓存处理。这允许服务器仅仅描述当用户的部分响应消息,此响应消息对于其他用户的请求无效
no-cache
指示请求或响应消息不能缓存
no-store
用于防止重要的信息被无意的发布。在请求消息中发送将使得请求和响应消息都不使用缓存
max-age
指示客户机可以接收生存期不大于指定时间(以秒为单位)的响应
min-fresh
指示客户机可以接收响应时间小于当前时间加上指定时间的响应
max-stale
指示客户机可以接收超出超时期间的响应消息。如果指定max-stale消息的值,那么客户机可以接收超出超时期指定值之内的响应消息
有关Session和Cookie的介绍,详细内容请参阅第10章“PHP会话管理”。
5.8.5 判断表单动作的技巧
表单可以通过同一个程序来分配应该要处理的动作,在表单中有不同的逻辑,要怎么判别使用者按下的按钮内容不过是个小问题。
其实只要通过提交按钮的name 就可以知道了,表单在提交出去的时候,只有按下的submit类型的按钮才会被送到表单数组去,所以只要判断按钮的值就可以知道使用者按下哪一个按钮,以如下表单为例:
当使用者按下“a”按钮的时候btn=a,按下“b”按钮,则btn=b。
另外也可以通过提交按钮的名字(name)来判断,请见如下代码:
这样只要POST/GET的参数里面有a或b,就可以知道按下的按钮是哪个。
print_r($_POST);
?>

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