Package com.nexaweb.server.messaging

Contains server side messaging APIs used for publishing and listening to messages.

See:
Description

Interface Summary

MessagingService

The MessagingService allows for system wide messaging.

Exception Summary

InvalidTopicException	Class InvalidTopicException
MessageDispatchException	MessageDispatchExceptions are thrown from the methods of MessagingService when messages can't be dispatched.
MessagingException	This is the base exception for all exceptions that may be thrown from Messaging components.

Package com.nexaweb.server.messaging Description

Contains server side messaging APIs used for publishing and listening to messages.

Nexaweb Internet Messaging Bus (IMB)

The messaging APIs give you access to the Internet Messaging Bus which connects multiple clients and servers allowing an exchange of messages between application components. To receive messages on a particular topic you first subscribe to that topic providing your own MessageListener. You can subscribe to a topic from the server or the client side. All messages published by clients always go to the server first from where they are dispatched to all topic subscribers. There are no direct client-to-client connections.

Note:The order of subscriber notification is not guaranteed.

Note:Each subscriber will receive all published messages in the order they were published.

Here is an example path a message takes when published on the client. Assume Client1 is subscribed to the topic "mytopic" and "message1" is a sample message.

• Client1 publishes "message1" on "mytopic"
• "message1" travels to the server that the Client1 is connected to
• The server dispatches the message to all "mytopic" subscribers ( including the client side subscribers of the client that published the message)
• Server side subscribers are called directly while client side subscribers are notified through a server side proxy. The proxy sends the message to each of the subscribed clients using any available connection from those clients. This implies that the clients will only receive the message if or when they make a connection to the server.
• When the message arrives on the client, the client side subscribers are notified.
• If clustering is enabled all subscribers managed by other servers in the cluster will also get notified (this includes all clients connected to those servers that contain subscribers for the topic)

Note:To subscribe to a topic or publish a message you need a connection to the server.

Note:If a client publishes a message on some request, the client's subscribers are not guaranteed to get notified after the corresponding response returns since message processing is asynchronous. So the client might get the message back either on the push connection (if one exists) or whenever it makes the next request to the server.

Server API

The API consists of only 1 service class: MessagingService. The service is used to perform system wide messaging from the server side. All MessageListeners subscribed on clients and servers will hear messages published through this service.

MessageListener can be extended to listen for messages sent across the Nexaweb Internet Messaging Bus (IMB). Subclasses should override the methods to receive messages of specific types. The onMessage() variant called will always correspond to the variant of the publsh() or send() method used to put the message on the IMB. All messaging on the server side is accessed through the MessagingService. All messaging on the client side is accessed through the NetService.

A reference to this service may be obtained by calling the static ServiceManager.getMessagingService() method.

Example Usage:

MessagingService messagingService = ServiceManager.getMessagingService();
messagingService.publish( "MyTopic.MySubTopic", "My message" );

Topics specified to methods defined by this interface must consist only of alphanumeric characters and the following ( '-', '.', '_', ':' ).

Server Performance Tuning

The dispatch of published messages to subscribers is serviced by the MessagingThreadPool. The settings for the pool can be adjusted in your application's nexaweb-server.xml. To get a feel for the pool performance you might want to look at the following jsp page contained in every Nexaweb application:

<your-appcontext>/Nexaweb/Services/index.jsp

There you can click on the MessagingService tab to see its statistics. Also you might want to take a look at the Thread Pool Report and All Performance Meters links. In the frame opening on the right search for the Message Thread Pool statistics. To get more information about all the different thread pool settings see nexaweb-server.xml documentation.