Messaging

• Identify scenarios that are appropriate to implementation using messaging, EJB, or both.
• List benefits of synchronous and asynchronous messaging.
• Select scenarios from a list that are appropriate to implementation using synchronous and asynchronous messaging.

Whats is messaging?

• Peer to peer facility
• Message agents provide facilities for creating,sending,reading and receiving messages.
• Enables distributed comm that is loosely coupled
• Messaging is used for comm between software applications or components.

JMS API

• Minimizes the set of concepts a prgmer must learn to use messaging products.
• Provides enough featurs to support sophisticated messaging apps.
• Maximises the portability of JMS apps across provider.
• Enables comm which is loosely coupled, asynchrounous and reliable.

Messaging Domain

1. Point to point
1. Build around the concept of message queues/senders and receivers.
2. Sender/Receiver of a message has no timing dependency.
3. Receiver acknowledge the successful processing of a message.
2. Publish & Subscribe
1. Each message can have multiple consumers.
2. Pub/Sub have a timing dependency. A client that subscribes to a topic can consume only messages that have been published after the subscription and must continue to be active to receive messages.

In pub/Sub model clients address message to a topic. Publisher and subscriber are generally anonymous and dynamically publish/subscribe. Topics retain messages only as long as it takes to distribute them to current subscribers.

Use pub/sub messaging when each message is consumed by 0,1 or *consumers.

• A JMS provider may implement one or both domains.
• A J2EE provider must implement both domains.

MOM
J2EE 1.2 Service provider was required to provide the JMS API interface and not the implementation.

J2EE 1.3 MOM is the integral part of the platform and developers can use the messaging features with other APIs.

JMS Arch
JMS Provider is the system that implements the JMS interface and provides admin constrol or features

JMS Client are prgms written in java that produce or consume messages.

Messages Are objects that communicate information between clients

Administered Objects are preconfigured objs created by the admin for the use of clients

• Destination objects
• Connection factories

Native Clients...
Notes from sun/cades scea/web