Websocket聊天实现

Question

Most of the demos of Websockets I see are of a chatroom application. I was wondering if it was possible to create more of an Instant Message implementation. The difference being that, in a chatroom application, numerous users connect and share messages with everyone, where, in an instant message application, users can connect to other users they choose.

I would like it to work without any plug-ins. I'm using JavaScript for the client side and Java EE for the server side. I looked into being able to change the endpoint URL but it seems that it has to be known at compile time. I also looked into using the Session object in the onMessage method but how would I know the session object of the user I need to send the message to? And I feel that would be a slow method to cycle through all session objects looking for the correct one. So, how could I create an Instant Message like application using WebSockets ?

Answer 1

Websockets are for communication between server and client using the HTTP protocol.

They are a particularly fit solution for any cross-language/cross-platform real time streaming/message passing related tasks, because the client(s)/consumers get notified instantly when any new data arrives, without the need of polling**.

The browser implements the client part of the specification.

Most server-side languages have libraries implementing the server part.

If you want basic instant messaging it's as easy as regular chat: you just have to change the list of recipients from everybody in the chat room to the particular client(s) on that conversation.

If you want to build a production grade instant messenger app, you should be aware you don't have to reinvent the wheel: You can built your messenger app on top of any XMPP library or code your own implementation of the protocol. Either way it takes away a good part of the design burden, letting you focus on the GUI or whatever extensions you consider appropriate.

If you are interested on the latter. check out atmosphere (specially, their plugins and extensions ) and this article (it's a little bit old, but it's good introductory stuff):

http://jfarcand.wordpress.com/2010/11/08/using-jquery-xmpp-and-atmosphere-to-cluster-your-websocketcomet-application/

(** If you wanted to use RMI instead, for example, you'd need a JVM on both server and client sides or the RMI-IIOP implementation for CORBA support, which is quite cumbersome for simple tasks. There are also some popular alternatives based on Comet , which is more of a set of techniques than a W3C standard: It's a little more difficult to use than websockets and has a few limitations, but has the benefit of working with legacy technology and implementing real time communication without the need of polling, by using HTTP 1.1 persistent connections)