OCEJBCD -6.Developing Java EE Applications Using Messaging

OCEJBCD (SCBCD) - 1Z0-895 - Enterprise JavaBeans Developer Certification

6.1. Review JMS technology

JMS (Java Messaging Service) is an API to send/receive messages :

1) Asynchronously:
JMS works asynchronously because it sends messages to the client without a previous request, also it sends messages without having to wait for a reply.

2) Loosely coupled: 
Provides vendor-independent access to messaging systems.

Messaging domain types:

• Point to point :
• Every message has a consumer
• The messages are requested from the queue by the consumer.

• Publish/Subscribe 
• Every message has several consumers
• The messages are pushed to the consumers without requesting.

  6.2. Describe the roles of the participants in the JMS API messaging system

Components is a JMS system:

• JMS Provider.- The messaging system
• JMS Clients .- Any java component that is producer or consumer of messages
• Producer
• Consumer(Listener and selectors)
• Messages .- the objects that contain the information.
• Administered objects.- Destinations and connection factories.
• Session.- single threaded context.
• Connection.- connection with JMS provider.
• Queue browsers.
• Exception handling .

6.3. Create a queue message producer

MessageProducer producer = session.createProducer(queue);

producer.send(message);

See JMS message producer from the oracle java EE tutorial

6.4. Create a synchronous message consumer

MessageConsumer consumer = session.createConsumer(queue);

connection.start();
Message m = consumer.receive();

See JMS message consumer from the oracle java EE tutorial

The message can be consumed synchronously or asynchronously. 
- synchronously : the consumer call the receive() method, that blocks until the message arrives
- asynchronously : the consumer call the onMessage() message listener method.

OCEJBCD (SCBCD) - 1Z0-895 - Enterprise JavaBeans Developer Certification