php isJson方法php版本错误

function isJson($string) {
 json_decode($string);
 return (json_last_error() == JSON_ERROR_NONE);
}

Actually, json_last_error is working on PHP 5.3 and upper versions but now i will use PHP 5.2 Server so this method will not work. Please tell me any alternative

json_decode will return NULL if json string cannot be decoded so might check with this:

function isJson($string) {
 return json_decode($string) != null;
}