Message Driven Bean MDB

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Message Driven Bean (MDB)

• Group 4

2
What is MDB?

• Message Driven Beans are EJB components that
  listen for message published on a JMS server.
• EJB 2.0 specification introduces a new kind of
  EJB called the MDB.
• The MDB model is designed to enable an EJB to be
  asynchronously invoked to handle the processing
  of incoming JMS messages.
• Message driven beans are a combination of Session
  beans and JMS clients.  

3
Messaging Systems MDB

• Message driven beans are enterprise beans that
  act as message consumers in the messaging system.
  
• MDB dont have a remote or a home interface.
• They are designed to interact with JMS API.
• MDB is used to integrate with the JMS, a service
  that allows clients to give orders to your EJB
  components without hanging around waiting for a
  response.
• Client applications access a message driven bean
  through JMS by sending messages to the JMS
  destination.

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JMS Service Illustrated
1. Client application opens a connection to a
JMS topic or queue
2. MDB registers a listener for a JMS topic or
queue
Java Messaging Service
JMS Topic
Client Application
4. The JMS topic or queue forwards the message
to the MDB, which takes action based on the
content of the message.
JMS Connection
EJB Container
ltlttopic listenergtgt message-driven bean
3. Client sends a message to the JMS topic or
queue. Once message is delivered, the client is
free to continue with other actions.
5
MDB Vs. Beans

• A session bean provides a remote interface that
  defines which methods can be invoked, a MDB
  doesnt.
• MDB doesnt use any of the component interfaces,
  because it is never accessed by method calls from
  other applications or beans.

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Pros Cons of MDB

• Pros
• EJB container provides all the plumbing necessary
  for MDBs to process messages concurrently. The
  result is multithreading environment that
  provides a substantial improvement in
  performance.
• Cons
• Not synchronous.
• MDBs are stateless, so if you need to preserve
  state between method invocations, you must use
  stateful session beans.