<?php

   session_start();

   header("Content-Type:text/html;charset:utf8");

   function set_token(){

       $_SESSION['token']=md5(microtime(true));

   }

   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['web'])){

            if(!valid_token()){

                      echo "请不要重复提交";

            }else{

                echo "提交成功,value:".$_POST['web'];

            }

   }else{

 ?>

  <center>

  <form method="post" action="">

    <input type="hidden" name="token" value="<?php echo $_SESSION['token'] ?>" />

    <input type="text"  class="input" name="web" value="www.baidu.com" />

    <input type="submit"   class="btn"  value="提交" />

  </form>

 </center>

 <?php

      }

 ?>