Cajac: /* Messaging Models */

2005-02-14T12:45:33Z

Messaging Models

← Older revision		Revision as of 12:45, 14 February 2005
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	=== Messaging Models ===		=== Messaging Models ===

			[[Image:Messagingmodels.png]]

	* Publish/Subscribe: several producers --> Topic --> several consumers		* Publish/Subscribe: several producers --> Topic --> several consumers

Cajac: /* Life Cycle */

2005-02-14T12:38:41Z

Life Cycle

← Older revision		Revision as of 12:38, 14 February 2005
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	=== Life Cycle ===		=== Life Cycle ===

			[[Image:Lifecycle.png]]
	* "does not exist" --> (1) --> "pooled" --> (2) --> "does not exist"
	* (1):
	** newInstance()
	** setMessageDrivenContext()
	** ejbCreate()
	* (2):
	** ejbRemove()
	* in the "pooled"-state, the onMessage()-method can be invoked

	=== Message Driven Bean Interface ===		=== Message Driven Bean Interface ===

217.184.47.180 at 14:21, 6 February 2005

2005-02-06T14:21:39Z

New page

== Overview ==

=== Motivation ===

* Performance
** no need to block when performing a request
** fire-and-forget
* Reliability
** middleman
** guaranteed delivery possible
* Support for multiple senders and receivers

=== Aspects ===

* Java Message Service (JMS)
** vendor-neutral API to access enterprise messaging systems
* Message-Driven Beans
** stateless, server-side, transaction-aware components for processing asynchronous messages

== Java Message Service (JMS) ==

=== Terms ===

* JMS client: applications that use JMS
* JMS provider: messaging system which is responsible for sending and routing of the messages
* JMS application: business system which consists of several clients and usually one provider
* MessageProducer: JMS client that sends messages
* MessageConsumer: JMS client that receives messages
* Messaging Service: is used to send messages from within EJB

=== Messaging Models ===

* Publish/Subscribe: several producers --> Topic --> several consumers
* Point-To-Point: several producers --> Queue --> one consumer

=== JMS API ===

* Locate the JMS driver: ConnectionFactory
* Create a JMS connection: Connection
* Create a JMS session: Session
* Locate the JMS destination: Destination (Queue/ Topic)
* Create JMS producer or consumer: MessageProducer/MessageConsumer
* Send or reveice message

=== JMS Message ===

* header: routing information, attributes
* properties: used for filtering (name-value pairs)
* body: the message
** types: TextMessage, MapMessage, ObjectMessage, StreamMessage, ByteMessage

=== Deployment Descriptor ===

* declare a JMS resource
** EJB 2.0
*** <resource-ref>: JNDI ENC name, interface type and protocol for authorisation (e.g. name=jms/TopicFactroy, type=javax.jms.TopicConnectionFactory, auth=Container)
*** <resoucre-env-ref>: name and type of the managed objects (e.g. name=jms/TicketTopic and type=javax.jms.Topic)
** EJB 2.1
*** <message-destination-ref>: destination of the messages and usage (Produces, Consumes, ConsumesProduces)

=== Example ===

...
TopicConnection tConnection=null;
TopicSession tSession=null;
TopicPublisher tPublisher=null;
try{
TopicConnectionFactory tConnectionFac=
(TopicConnectionFactory)Lookup.lookup(„java:comp/env/jms“);
tConnection=tConnectionFac.createTopicConnection();
tSession=tConnection.createTopicSession(false,
Session.AUTO_ACKNOWLEDGE);
Topic topic=(Topic)Lookup.lookup(„TestTopic“);
tPublisher=tSession.createPublisher(topic);
String text=“Message“;
Message message=tSession.createTextMessage(text);
tPublisher.send(message);
} catch (JMSException jes){ ...
} finally {
// close()
}

== Message Driven Beans ==

=== Introduction ===

* does not have a home interface, local home interface, remote interface, local interface
* single, weakly typed business method (onMessage())
* do not have any return values
* cannot send exceptions back to clients
* are stateless
* can be durable or nondurable subscribers

=== Life Cycle ===

* "does not exist" --> (1) --> "pooled" --> (2) --> "does not exist"
* (1):
** newInstance()
** setMessageDrivenContext()
** ejbCreate()
* (2):
** ejbRemove()
* in the "pooled"-state, the onMessage()-method can be invoked

=== Message Driven Bean Interface ===

package javax.ejb;
public interface MessageDrivenBean extends javax.ejb.EnterpriseBean{
public void setMessageDrivenContext(MessageDrivenContext context)
throws EJBException;
public void ejbRemove() throws EJBException;
}

=== Message Driven Context ===

* extends EJBContext
* only setRollbackOnly(), getRollbackOnly() make sense
* getEJBHome() and getEJBLocalHome() throw a RuntimeException if invoked
* getCallerPrincipal() and isCallerInRole() throw a RuntimeException if invoked

=== Message Listener ===

package javax.jms;
public interface MessageListener {
public void onMessage(Message message);
}

=== Deployment Descriptor ===

* EJB 2.0
** declared in <message-driven>; ejb-name, ejb-class, transaction-type as session or entity bean
** <message-selector>: select which messages are processed
** <acknowledge-mode>: e.g. auto-acknowledge, dups-ok-acknowledge
** <subscription-durability>: durable or not (messages are delivered later on if a consumer is disconnected or not)
** <message-driven-destination>: type of destination (Topic/Queue)

* EJB 2.1
** <activation-config>: general declaration of properties (e.g. substitutes message-selector, acknowledge-mode and subscription-durability in EJB 2.0)
** <messaging-type>: javax.jms.MessageListener für JMS
** <messaging-destination-type>: important for COnnector-Based beans (don't use JMS)

=== Example ===

...
public abstract class MDBExample implements MessageDrivenBean, MessageListener {
...
public void ejbCreate() throws EJBException{
... // create Connection, Session, Queue
qReceiver=qSession.createReceiver(queue);
qReceiver.setMessageListener(this);
qConnection.start();
...
}
public void onMessage(Message message){
...
// if (message instanceof TextMessage){ ... }
...
}
... // setMessageDrivenContext(), ejbRemove()
}

=== MDB vs. Session & Entity Bean ===

* Entity and Session Beans should not receive messages
* impossible to write a session or entity bean that is driven by incoming messages
* receive()-method blocks java threads

Asynchronous Messaging - Revision history

Cajac: /* Messaging Models */

Cajac: /* Life Cycle */

217.184.47.180 at 14:21, 6 February 2005