在Java中将JSON类型转换为字节数组格式

我想在UDP协议中使用字节格式发送数据时遇到问题，问题是当我尝试使用json对象类型创建数据时，我无法获取数据的字节格式，这是我的示例代码:

I have a problem when I want to sending data using byte format in UDP protocol, the problem is when I try to create a data with type json object, I can't get the byte format of my data this is my sample code:

    JSONObject obj = new JSONObject();
    obj.put("name", "foo");
    obj.put("num", new Integer(100));
    obj.put("balance", new Double(1000.21));
    obj.put("is_vip", new Boolean(true));
    obj.put("nickname",null);

    sendData = obj.getBytes(); //this is error because not have methos getBytes();

我知道我的问题，但是我找不到如何将json对象转换为字节的方法，有什么建议吗?

i know my problem but i can't found how to convert json object to byte, any suggestion ?