防止php重复提交表单更安全的方法

1. Token.php  
   
   <?php  
   
   /*
    * Created on 2013-3-25
    *
    * To change the template for this generated file go to
    * Window - Preferences - PHPeclipse - PHP - Code Templates
    */
   function getToken($len = 32, $md5 = true) {
       # Seed random number generator
       # Only needed for PHP versions prior to 4.2
       mt_srand((double) microtime() * 1000000);
       # Array of characters, adjust as desired
       $chars = array (
           'Q',
           '@',
           '8',
           'y',
           '%',
           '^',
           '5',
           'Z',
           '(',
           'G',
           '_',
           'O',
           '`',
           'S',
           '-',
           'N',
           '<',
           'D',
           '{',
           '}',
           '[',
           ']',
           'h',
           ';',
           'W',
           '.',
           '/',
           '|',
           ':',
           '1',
           'E',
           'L',
           '4',
           '&',
           '6',
           '7',
           '#',
           '9',
           'a',
           'A',
           'b',
           'B',
           '~',
           'C',
           'd',
           '>',
           'e',
           '2',
           'f',
           'P',
           'g',
           ')',
           '?',
           'H',
           'i',
           'X',
           'U',
           'J',
           'k',
           'r',
           'l',
           '3',
           't',
           'M',
           'n',
           '=',
           'o',
           '+',
           'p',
           'F',
           'q',
           '!',
           'K',
           'R',
           's',
           'c',
           'm',
           'T',
           'v',
           'j',
           'u',
           'V',
           'w',
           ',',
           'x',
           'I',
           '$',
           'Y',
           'z',
           '*'
       );
       # Array indice friendly number of chars;
       $numChars = count($chars) - 1;
       $token = '';
       # Create random token at the specified length
       for ($i = 0; $i < $len; $i++)
           $token .= $chars[mt_rand(0, $numChars)];
       # Should token be run through md5?
       if ($md5) {
           # Number of 32 char chunks
           $chunks = ceil(strlen($token) / 32);
           $md5token = '';
           # Run each chunk through md5
           for ($i = 1; $i <= $chunks; $i++)
               $md5token .= md5(substr($token, $i * 32 - 32, 32));
           # Trim the token
           $token = substr($md5token, 0, $len);
       }
       return $token;
   }
   ?>
   form.php  
   
   <?php
   include_once("token.php");
   $token = getToken();
   session_start();
   $_SESSION['token'] = $token;
   ?>
   <form action="action.php" method="post"
   <input type="hidden" name="token" value="<?=$token?>" />
   <!-- 其他input submit之类的 -->
   </form>
   action.php  
   
   <?php
   session_start();
   if($_POST['token'] == $_SESSION['token']){
       unset($_SESSION['token']);
       echo "这是一个正常的提交请求";
   }else{
       echo "这是一个非法的提交请求";
   }
   ?>