PHP POST方法进入RESTful Web服务

The simple thing I want to do is to POST into a RESTful web service using PHP. I have been able to GET the values using PHP, now I want to POST into it. This is the PHP file using curl.

<?php
    $username = $_POST['username'];
    $password = $_POST['password'];

    $url = "http://localhost:8080/WMWS/webresources/entity.userregistration";

    $data = array('username' => $username, 'password' => $password);
    $initializeCurl = curl_init();
    curl_setopt($initializeCurl, CURLOPT_URL, $url);
    curl_setopt($initializeCurl, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($initializeCurl, CURLOPT_POST, true);
    curl_setopt($initializeCurl, CURLOPT_POSTFIELDS, $data);
    $response = curl_exec($initializeCurl);
    curl_close($initializeCurl);
?>

I am using XAMPP and I have enabled curl in PHP.ini file. Whenever I insert values into the form input of HTML and click the submit button, it only return the PHP code on the browser and does nothing like insertion. How can I handle it?

This is is the HTML file:

<body>
    <form action = "posttoxml.php" method = "POST">
        <label for = "username">Username</label>
        <input type = "text" name = "username" />
        <label for = "password">Password</label>
        <input type = "password" name = "password" />
        <button id = "register" name = "register">Register</button>
    </form>
</body>