PHP 防止表单重复提交

<?php  
/* 
* PHP简单利用token防止表单重复提交 
* 此处理方法纯粹是为了给初学者参考 
*/ 
session_start();  
 
var_dump($_POST);
function set_token() {  
     $_SESSION['token'] = md5(microtime(true));  
     var_dump($_SESSION['token']);
}  
   
function valid_token() {  
    $return = $_REQUEST['token'] === $_SESSION['token'] ? true : false;  
    set_token();  
    return $return;  
}  
   
//如果token为空则生成一个token  
if(!isset($_SESSION['token']) || $_SESSION['token']=='') {  
    set_token();  
}  
   
if(isset($_POST['test'])){  
    if(!valid_token()){  
        echo "token error";  
    }else{  
        echo '成功提交，Value:'.$_POST['test'];  
    }  
}  
?>  
<form method="post" action="">  
    <input type="hidden" name="token" value="<?php echo $_SESSION['token']?>">  
    <input type="text" name="test" value="Default">  
    <input type="submit" value="提交" />  
</form>