Java客户端-服务器聊天协议设计

Question

I need to create a protocol for client-server chat on Java. I use xml to encode messages between them, but I can't decide how to return decoded data to server.

First time, i created many object implements IAction (eg Auth object represents a packet, about new user in chat) which vary depending on their content. So, when server receives a socket, it calls my public IAction decode(String s) and then, server should determine what object it is:

if (myIAction instanceof Auth) {
   server.doMagicAuth((Auth) myIAction);
}

but it was looking ugly to me coz of typecasting and many ifes

Another approach was to create one common object, called Packet , that can contain intValue , floatValue , stringValue etc. And also it had a flag, that talked about what kind of packet it is. But it was the worst idea coz of collisions. For example, how to send 2 int values it this packet? eg password and users_id?

And the latest idea was to observe server. Server should have many overloaded public void action(IAction a) methods ( action(Auth a) ... etc), and protocol should notify a server depending on what kind of packet it is.

And i cant decide, what method to use. Maybe you have some completely different ideas?

Answer 1

A chat client-server application usually does not send/receive 2 ints or 3 floats or anything like that but just strings. These days I would probably either send JSON objects serialized as strings or just plain strings.

If using XML is a firm requirement you need to define some XML format
(possibly through some XSD even though that's not mandatory in your case)
and stick to that format. Example:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<message text="Hello"/>

When this is sent from any client, you take it on the server side,
get the text value and send it from the server to all connected clients.
That is all they want from you, I believe.