Programming on EJB3 with Jboss server. (PART2)

   Part 2 of these series articles describe how to coding on MDB with EJB3.

   MDB is the MVP(most valuable player) both in previous EJB version and EJB3. Although coding with MDB is simple in EJB2.x, EJB3 make it much more friendly to you. Let's get to the point.
    Following is what you should know before write the first MDB in EJB3:

•     MDB is just a POJO which must implement javax.jms.MessageListener directly or indirectly.
•     MDB can not extends from another MDB. This should be fine, because each MDB should has its own destination or queue.
•     Do not throw runtime exception which will cause the instance of this MDB to be destroyed.
•     One no argument construct method like session bean does.

    Let's see how everything goes on, first of all is the new version EJB3 MDB example source code:
   

 1 package com.ramon.expejb3.session.impl;
 2 
 3 import javax.annotation.PostConstruct;
 4 import javax.annotation.PreDestroy;
 5 import javax.annotation.Resource;
 6 import javax.ejb.ActivationConfigProperty;
 7 import javax.ejb.MessageDriven;
 8 import javax.jms.JMSException;
 9 import javax.jms.Message;
10 import javax.jms.MessageListener;
11 import javax.jms.Queue;
12 import javax.jms.QueueConnection;
13 import javax.jms.QueueConnectionFactory;
14 import javax.jms.QueueSender;
15 import javax.jms.QueueSession;
16 import javax.jms.Session;
17 import javax.jms.TextMessage;
18 
19 @MessageDriven(
20         name = "greetingSender",
21         activationConfig = {
22                 @ActivationConfigProperty(propertyName="destinationType", propertyValue="javax.jms.Queue"),
23                 @ActivationConfigProperty(propertyName="destination", propertyValue="queue/ramonQueue")
24         }
25 )
26 public class GreetingSenderMDB implements MessageListener {
27     
28     @Resource(mappedName="java:/XAConnectionFactory")
29     private QueueConnectionFactory qconFactory;
30     
31     @Resource(mappedName="queue/ramonRecoderQueue")
32     private Queue queue;
33     
34     private QueueConnection qcon;
35     
36     private QueueSession qsession;
37     
38     private QueueSender qsender;
39     
40     private TextMessage msg;
41     
42     @PostConstruct
43     public void init() {
44         try {
45             qcon = qconFactory.createQueueConnection();
46             qsession = qcon.createQueueSession(false, Session.AUTO_ACKNOWLEDGE);
47             qsender = qsession.createSender(queue);
48             msg = qsession.createTextMessage();
49             qcon.start();
50             System.out.println(this.getClass() + " init done.");
51         } catch (JMSException e) {
52             // TODO Auto-generated catch block
53             e.printStackTrace();
54         }
55     }
56     
57     private void send(String message) throws JMSException {
58         msg.setText(message);
59         qsender.send(msg);
60     }
61     
62     public void onMessage(Message arg0) {
63         TextMessage txt = (TextMessage)arg0;
64         try {
65             System.out.println("Message '" + txt.getText() + "' has been received.");
66             send(txt.getText());
67             System.out.println(">>> Record msg for '" + txt.getText() + "' has been sent out.");
68         } catch (JMSException e) {
69             // TODO Auto-generated catch block
70             e.printStackTrace();
71         }
72     }
73     
74     @PreDestroy
75     public void gc() {
76         try {
77             qcon.close();
78             System.out.println("GC for " + this.getClass() + ".");
79         } catch (JMSException e) {
80             // TODO Auto-generated catch block
81             e.printStackTrace();
82         }
83     }
84 
85 }
86 

    This is a smiple example, we use @MessageDriven to make this POJO a EJB3 MDB, the "destinationType" attribute make this MDB register itself to a JMS queue not a topic, the "destination" attribute tell the MDB where to listen for the queue, it's a jndi name of the queue you specified in your container. Other part of this code is also self-explanation, you should just focus on how to implement the MessageListener interface -- the onMessage() method.

    For our example, the logic in onMessage() is simple, described as follow:
    1. Receive message from client invocation.
    2. Create a new message according to received message and then send it out to another JMS queue.
    Let's see the source code:
   

 1    public void onMessage(Message arg0) {
 2         TextMessage txt = (TextMessage)arg0;
 3         try {
 4             System.out.println("Message '" + txt.getText() + "' has been received.");
 5             send(txt.getText());
 6             System.out.println(">>> Record msg for '" + txt.getText() + "' has been sent out.");
 7         } catch (JMSException e) {
 8             // TODO Auto-generated catch block
 9             e.printStackTrace();
10         }
11     }

    Yup, it's simple, just like the ordinary JMS listener implementation. Let's see how does the send() method in the line 5 get the ConnectionFactory and Queue object and then send message to another queue. EJB3 give us an anotation named "Resource", with this anotation container can inject resource such as DataSourceConnectionFactory, JMSConnectionFactory... into our bean instance, we use this anotation to inject JMSConnectionFactory and JMSQueue, see the code snatch:
   

1     @Resource(mappedName="java:/XAConnectionFactory")
2     private QueueConnectionFactory qconFactory;
3     
4     @Resource(mappedName="queue/ramonRecoderQueue")
5     private Queue queue;

    With this anotation we can remove the boring JNDI lookup code, that's really great, because I always copy and paste for JNDI lookup code:) What important is that you should use the "mappedName" attribute instead of the "name" attribute when you want to lookup some JNDI, because the "name" attribute always triger an "env" prefix before the actual JNDI name you specified.

    Other part of this code is simple, so I just paste the code here, GreetingRecordMDB.java:

 1 package com.ramon.expejb3.session.impl;
 2 
 3 import javax.ejb.ActivationConfigProperty;
 4 import javax.ejb.MessageDriven;
 5 import javax.jms.JMSException;
 6 import javax.jms.Message;
 7 import javax.jms.MessageListener;
 8 import javax.jms.TextMessage;
 9 
10 @MessageDriven(
11         name = "greetingRecoder",
12         activationConfig = {
13                 @ActivationConfigProperty(propertyName="destinationType", propertyValue="javax.jms.Queue"),
14                 @ActivationConfigProperty(propertyName="destination", propertyValue="queue/ramonRecoderQueue")
15         }
16 )
17 public class GreetingRecordMDB implements MessageListener {
18 
19     public void onMessage(Message arg0) {
20         TextMessage msg = (TextMessage)arg0;
21         try {
22             String name = msg.getText();
23             System.out.println(name + "has been recorded.");
24         } catch (JMSException e) {
25             // TODO Auto-generated catch block
26             e.printStackTrace();
27         }
28     }
29 
30 }
31 

    The client side code GreetingSenderMDBTest.java:

 1 package com.ramon.expejb3.session.impl;
 2 
 3 import javax.jms.JMSException;
 4 import javax.jms.Queue;
 5 import javax.jms.QueueConnection;
 6 import javax.jms.QueueConnectionFactory;
 7 import javax.jms.QueueSender;
 8 import javax.jms.QueueSession;
 9 import javax.jms.Session;
10 import javax.jms.TextMessage;
11 import javax.naming.Context;
12 
13 import com.ramon.expejb3.session.ExpEJB3BaseTestCase;
14 
15 public class GreetingSenderMDBTest extends ExpEJB3BaseTestCase {
16 
17     private QueueConnectionFactory qconFactory;
18     private QueueConnection qcon;
19     private QueueSession qsession;
20     private QueueSender qsender;
21     private Queue queue;
22     private TextMessage msg;
23 
24     @Override
25     protected void setUp() throws Exception {
26         // TODO Auto-generated method stub
27         super.setUp();
28         Context ctx = this.getContext();
29         qconFactory = (QueueConnectionFactory) ctx
30                 .lookup("java:/XAConnectionFactory");
31         qcon = qconFactory.createQueueConnection();
32         qsession = qcon.createQueueSession(false, Session.AUTO_ACKNOWLEDGE);
33         queue = (Queue) ctx.lookup("queue/ramonQueue");
34         qsender = qsession.createSender(queue);
35         msg = qsession.createTextMessage();
36         qcon.start();
37     }
38 
39     public void send(String message) throws JMSException {
40         msg.setText(message);
41         qsender.send(msg);
42     }
43 
44     public void close() throws JMSException {
45         qcon.close();
46     }
47 
48     @Override
49     protected void tearDown() throws Exception {
50         // TODO Auto-generated method stub
51         super.tearDown();
52     }
53 
54     public void testOnMessage() {
55         try {
56             for (int i = 0; i < 5; i++) {
57                 String msg = "Ramon " + i;
58                 send(msg);
59                 System.out.println("send msg: " + msg);
60             }
61             send("end");
62         } catch (JMSException e) {
63             // TODO Auto-generated catch block
64             e.printStackTrace();
65         } finally {
66             try {
67                 close();
68             } catch (JMSException e) {
69                 // TODO Auto-generated catch block
70                 e.printStackTrace();
71             }
72         }
73     }
74 
75 }
76 

    The JMS configuration snatch in file "jbossmq-destinations-service.xml" of Jboss server:

 1 <mbean code="org.jboss.mq.server.jmx.Queue"
 2      name="jboss.mq.destination:service=Queue,name=ramonQueue">
 3     <depends optional-attribute-name="DestinationManager">jboss.mq:service=DestinationManager</depends>
 4     <depends optional-attribute-name="SecurityManager">jboss.mq:service=SecurityManager</depends>
 5     <attribute name="MessageCounterHistoryDayLimit">-1</attribute>
 6     <attribute name="SecurityConf">
 7       <security>
 8         <role name="guest" read="true" write="true"/>
 9         <role name="publisher" read="true" write="true" create="false"/>
10         <role name="noacc" read="false" write="false" create="false"/>
11       </security>
12     </attribute>
13   </mbean>
14   
15   <mbean code="org.jboss.mq.server.jmx.Queue"
16      name="jboss.mq.destination:service=Queue,name=ramonRecoderQueue">
17     <depends optional-attribute-name="DestinationManager">jboss.mq:service=DestinationManager</depends>
18     <depends optional-attribute-name="SecurityManager">jboss.mq:service=SecurityManager</depends>
19     <attribute name="MessageCounterHistoryDayLimit">-1</attribute>
20     <attribute name="SecurityConf">
21       <security>
22         <role name="guest" read="true" write="true"/>
23         <role name="publisher" read="true" write="true" create="false"/>
24         <role name="noacc" read="false" write="false" create="false"/>
25       </security>
26     </attribute>
27   </mbean>