/**
 * 返回Json数据
 * @param int $code
 * @param string $message
 * @param array $data
 * @return string
 */
public function retJson($code,$message = '',$data = array())
{
    if(!is_numeric($code))
    {
        return '';
    }

    $result=array(
        'code' => $code,
        'message' => $message;
        'data' => $data
    );

    echo json_encode($result);
    exit;
}