How to resolve PHP form repeat submission _php tips

Repeated submission is a problem we often encounter in development, in addition to using JS to prevent the recurrence of forms, but also can use PHP to prevent duplicate submissions Oh.

<?php
 /* * PHP How to prevent the form of duplicate
 submission
/session_start ();
if (Empty ($_session[' IP ')) {//First write operation to determine whether the IP address is logged, to know whether to write to the database
  $_session[' ip ' = $_server[' remote_addr ']; First write, a foreshadowing of the back refresh or back
  //...........//write the database operation
} else {//already has the first write operation, and then no longer write to the database
  echo ' Please do not refresh and rewind again '; Write some hints or other things that have been written
}
?>

Specific principles
Session range variable token to prevent.
1. Open session:
session_start ();
2. If a form is submitted

 if (Isset ($token))

Token is included in the form as a hidden.

<input type= "hidden" name= "token" value= "<?php echo $token;?>"/>

3. If you are submitting a form repeatedly

if ($_session["token"]!= $token) { 
  //Do not allow duplicate submissions in this processing 
  //Header ("Location:". $_server[' php_self ']); 
} else { 
  //normal form submission, here processing 
  //echo "submitted";  
}

4. Set token value
$token = Mt_rand (0,1000000);
2$_session[' token ' = $token;

The above is about how to solve the PHP form to repeat the implementation method of submission, I hope to help you learn.