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Simple MDB

Below is a fun app, a chat application that uses JMS. We create a message driven bean, by marking our class with @MessageDriven. A message driven bean has some similarities with a stateless session bean, in the part that it is pooled too.

Well, lets tell our chat-app to listen for incoming messages. That we do by implementing MessageListener and overriding the onMessage(Message message).

Then this app "listens" for incoming messages, and the messages picked up are processed by onMessage(Message message) method.

That finishes our message driven bean implementation. The "processing" part could be anything that fits your business-requirement.

In this case, it is to respond to the user. The respond method shows how a Message can be sent.

This sequence diagram shows how a message is sent.

mdb flow

ChatBean

package org.superbiz.mdb;

import javax.annotation.Resource;
import javax.ejb.MessageDriven;
import javax.jms.Connection;
import javax.jms.ConnectionFactory;
import javax.jms.DeliveryMode;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageListener;
import javax.jms.MessageProducer;
import javax.jms.Queue;
import javax.jms.Session;
import javax.jms.TextMessage;

@MessageDriven
public class ChatBean implements MessageListener {

    @Resource
    private ConnectionFactory connectionFactory;

    @Resource(name = "AnswerQueue")
    private Queue answerQueue;

    public void onMessage(Message message) {
        try {

            final TextMessage textMessage = (TextMessage) message;
            final String question = textMessage.getText();

            if ("Hello World!".equals(question)) {

                respond("Hello, Test Case!");
            } else if ("How are you?".equals(question)) {

                respond("I'm doing well.");
            } else if ("Still spinning?".equals(question)) {

                respond("Once every day, as usual.");
            }
        } catch (JMSException e) {
            throw new IllegalStateException(e);
        }
    }

    private void respond(String text) throws JMSException {

        Connection connection = null;
        Session session = null;

        try {
            connection = connectionFactory.createConnection();
            connection.start();

            // Create a Session
            session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);

            // Create a MessageProducer from the Session to the Topic or Queue
            MessageProducer producer = session.createProducer(answerQueue);
            producer.setDeliveryMode(DeliveryMode.NON_PERSISTENT);

            // Create a message
            TextMessage message = session.createTextMessage(text);

            // Tell the producer to send the message
            producer.send(message);
        } finally {
            // Clean up
            if (session != null) session.close();
            if (connection != null) connection.close();
        }
    }
}

ChatBeanTest

package org.superbiz.mdb;

import junit.framework.TestCase;

import javax.annotation.Resource;
import javax.ejb.embeddable.EJBContainer;
import javax.jms.Connection;
import javax.jms.ConnectionFactory;
import javax.jms.JMSException;
import javax.jms.MessageConsumer;
import javax.jms.MessageProducer;
import javax.jms.Queue;
import javax.jms.Session;
import javax.jms.TextMessage;

public class ChatBeanTest extends TestCase {

    @Resource
    private ConnectionFactory connectionFactory;

    @Resource(name = "ChatBean")
    private Queue questionQueue;

    @Resource(name = "AnswerQueue")
    private Queue answerQueue;

    public void test() throws Exception {
        EJBContainer.createEJBContainer().getContext().bind("inject", this);


        final Connection connection = connectionFactory.createConnection();

        connection.start();

        final Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);

        final MessageProducer questions = session.createProducer(questionQueue);

        final MessageConsumer answers = session.createConsumer(answerQueue);


        sendText("Hello World!", questions, session);

        assertEquals("Hello, Test Case!", receiveText(answers));


        sendText("How are you?", questions, session);

        assertEquals("I'm doing well.", receiveText(answers));


        sendText("Still spinning?", questions, session);

        assertEquals("Once every day, as usual.", receiveText(answers));
    }

    private void sendText(String text, MessageProducer questions, Session session) throws JMSException {

        questions.send(session.createTextMessage(text));
    }

    private String receiveText(MessageConsumer answers) throws JMSException {

        return ((TextMessage) answers.receive(1000)).getText();
    }
}

Running

-------------------------------------------------------
 T E S T S
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Running org.superbiz.mdb.ChatBeanTest
Apache OpenEJB 4.0.0-beta-1    build: 20111002-04:06
http://tomee.apache.org/
INFO - openejb.home = /Users/dblevins/examples/simple-mdb
INFO - openejb.base = /Users/dblevins/examples/simple-mdb
INFO - Using 'javax.ejb.embeddable.EJBContainer=true'
INFO - Configuring Service(id=Default Security Service, type=SecurityService, provider-id=Default Security Service)
INFO - Configuring Service(id=Default Transaction Manager, type=TransactionManager, provider-id=Default Transaction Manager)
INFO - Found EjbModule in classpath: /Users/dblevins/examples/simple-mdb/target/classes
INFO - Beginning load: /Users/dblevins/examples/simple-mdb/target/classes
INFO - Configuring enterprise application: /Users/dblevins/examples/simple-mdb
WARN - Method 'lookup' is not available for 'javax.annotation.Resource'. Probably using an older Runtime.
INFO - Auto-configuring a message driven bean ChatBean destination ChatBean to be destinationType javax.jms.Queue
INFO - Configuring Service(id=Default MDB Container, type=Container, provider-id=Default MDB Container)
INFO - Auto-creating a container for bean ChatBean: Container(type=MESSAGE, id=Default MDB Container)
INFO - Configuring Service(id=Default JMS Resource Adapter, type=Resource, provider-id=Default JMS Resource Adapter)
INFO - Configuring Service(id=Default JMS Connection Factory, type=Resource, provider-id=Default JMS Connection Factory)
INFO - Auto-creating a Resource with id 'Default JMS Connection Factory' of type 'javax.jms.ConnectionFactory for 'ChatBean'.
INFO - Auto-linking resource-ref 'java:comp/env/org.superbiz.mdb.ChatBean/connectionFactory' in bean ChatBean to Resource(id=Default JMS Connection Factory)
INFO - Configuring Service(id=AnswerQueue, type=Resource, provider-id=Default Queue)
INFO - Auto-creating a Resource with id 'AnswerQueue' of type 'javax.jms.Queue for 'ChatBean'.
INFO - Auto-linking resource-env-ref 'java:comp/env/AnswerQueue' in bean ChatBean to Resource(id=AnswerQueue)
INFO - Configuring Service(id=ChatBean, type=Resource, provider-id=Default Queue)
INFO - Auto-creating a Resource with id 'ChatBean' of type 'javax.jms.Queue for 'ChatBean'.
INFO - Configuring Service(id=Default Managed Container, type=Container, provider-id=Default Managed Container)
INFO - Auto-creating a container for bean org.superbiz.mdb.ChatBeanTest: Container(type=MANAGED, id=Default Managed Container)
INFO - Auto-linking resource-ref 'java:comp/env/org.superbiz.mdb.ChatBeanTest/connectionFactory' in bean org.superbiz.mdb.ChatBeanTest to Resource(id=Default JMS Connection Factory)
INFO - Auto-linking resource-env-ref 'java:comp/env/AnswerQueue' in bean org.superbiz.mdb.ChatBeanTest to Resource(id=AnswerQueue)
INFO - Auto-linking resource-env-ref 'java:comp/env/ChatBean' in bean org.superbiz.mdb.ChatBeanTest to Resource(id=ChatBean)
INFO - Enterprise application "/Users/dblevins/examples/simple-mdb" loaded.
INFO - Assembling app: /Users/dblevins/examples/simple-mdb
INFO - Jndi(name="java:global/EjbModule1515710343/org.superbiz.mdb.ChatBeanTest!org.superbiz.mdb.ChatBeanTest")
INFO - Jndi(name="java:global/EjbModule1515710343/org.superbiz.mdb.ChatBeanTest")
INFO - Created Ejb(deployment-id=org.superbiz.mdb.ChatBeanTest, ejb-name=org.superbiz.mdb.ChatBeanTest, container=Default Managed Container)
INFO - Created Ejb(deployment-id=ChatBean, ejb-name=ChatBean, container=Default MDB Container)
INFO - Started Ejb(deployment-id=org.superbiz.mdb.ChatBeanTest, ejb-name=org.superbiz.mdb.ChatBeanTest, container=Default Managed Container)
INFO - Started Ejb(deployment-id=ChatBean, ejb-name=ChatBean, container=Default MDB Container)
INFO - Deployed Application(path=/Users/dblevins/examples/simple-mdb)
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 1.547 sec

Results :

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

APIs Used