sending message from xmpp server vysper in java

Question

I have set up simple server and client, but i don't no how to send message from xmpp server to client. Please give me some help. If possible then suggest me some links.

Answer 1

This is a question which surprisingly often comes up for Vysper. There are several reasons for even asking the question, one particular reason I think is that a HTTP web server in fact works in such a way that it creates and sends content (HTML, CSS etc.) to the agent a.k.a. web browser.

In message-based protocols like email and chat this is a bit different.

Emails are created and consumed by the agents a.k.a. the email clients. Servers mostly only act as Message Brokers (http://en.wikipedia.org/wiki/Message_broker), including aspects like authentication, filtering, storing etc. Rarely do they produce their own email messages out of themselves. Often, a few central accounts (e.g. [email protected], [email protected]) create most of the emails, meaning that the actual messages are produced by an email client and delivered by the server on behalf of the client. (Additionally, email/SMTP has the specialty that clients send out email directly to the receiver's email server which is a nightmare going by the name of /spam/.)

In general, XMPP is no difference here. XMPP chat clients connect and send out and receive messages. The XMPP server brokers the messages. So, to answer your question, in most cases it is sufficient and suggested to have a central account communicating with all the other accounts. It's the simplest and best solution.

However, XMPP offers a little bit more than chat. It has extensions for wizzard-like workflows based on forms, publish/subscribe and administation/commands.

You can add your own extension, if you really need to:

For example, have a look at the VCard extension here: http://svn.apache.org/viewvc/mina/vysper/trunk/server/core/src/main/java/org/apache/vysper/xmpp/modules/extension/xep0054_vcardtemp/

Foremost, I'd recommend to subclass org.apache.vysper.xmpp.modules.core.base.handler.DefaultIQHandler This is like implementing your own Servlet by subclassing DefaultServlet. It contains the XMPP stanza logic you want to provide.

Additionally, you need to plug your handler into the server. This is best done by following the example in VcardTempModule, which

1. provides a Handler instance and registers it
2. initializes persistence (or any other backend connection you might need)
3. makes your extension's namespace known and announces your IQ stuff in the Service Discovery

If you need persistence, have a look at the VcardTempPersistenceManager.

What remains to be done is to make your Module known to the server. If you use Spring, add one line to the Spring configuration. If you use an embedded approach, you'd need to call the equivalent to server.addModule(new VcardTempModule()); like it is done in org.apache.vysper.xmpp.server.ServerMain

Now, if you'd want to emit new Stanzas (messages) which are not a reaction to other Stanzas going through the server, you'd also need to start off your own Thread which is able to create and send Stanzas.

But again, the preferred way is to have the clients create all messages.