XML-Output of User

UserData.php

<?php

class UserData extends \Frontend
{
    public function __construct($intId, $strLanguage=null)
    {
        parent::__construct();
        $this->import('Database');
    }
  
    protected function compile()
    {
        $user = \Input::get('user');
          
        if ( $user === null ) 
        {
            $this->Template = new \Template('mod_message');
            $this->Template->type = 'error';
            $this->Template->message = $GLOBALS['TL_LANG']['ERR']['noUserGiven'];

            return;
        }
        
        $objUser = \Database::getInstance()->prepare( "SELECT username, message_count, last_activity, user_state, alerts_unread, conversations_unread FROM xf_user WHERE username='?'" )->limit(1)->execute($user);
        
        if (!$objUser->numRows)
        {
            throw new \UnderflowException('No UserData found by '.$user);
        }
        
        //Create XML
        $dom = new DOMDocument('1.0', 'utf-8');
        $root = $dom->createElement('UserData');
        $dom->appendChild($root);
        
        $root->appendChild($dom->createElement("username", $objUser->username));
        $root->appendChild($dom->createElement("message_count", $objUser->message_count));
        $root->appendChild($dom->createElement("last_activity", $objUser->last_activity));
        $root->appendChild($dom->createElement("user_state", $objUser->user_state));
        
        header('Content-type: text/xml; charset=utf-8');
        echo $dom->saveXML();
    }  
}

$objUserData = new UserData;
$objUserData->compile;