JMS : queues on glassfish

Setting up GlassFish for JMS and Working with Message Queues

https://www.packtpub.com/article/setting-glassfish-jms-working-with-message-queues

The Java Messaging API (JMS) provides a mechanism for Java EE applications to send messages to each other. JMS applications do not communicate directly, instead message producers send messages to a destination and message consumers receive the message from the destination.

The message destination is a message queue when the point-to-point (PTP) messaging domain is used, or a message topic when the publish/subscribe (pub/sub) messaging domain is used.

In this article by David Heffelfinger, author of the book Java EE 6 with GlassFish 3 Application Server, we will cover the following topics:

• Setting up GlassFish for JMS
• Working with message queues

(For more resources on Java, see here.)

Setting up GlassFish for JMS

Before we start writing code to take advantage of the JMS API, we need to configure some GlassFish resources. Specifically, we need to set up a JMS connection factory, a message queue, and a message topic.

Setting up a JMS connection factory

The easiest way to set up a JMS connection factory is via GlassFish's web console. The web console can be accessed by starting our domain, by entering the following command in the command line:

asadmin start-domain domain1

Then point the browser to http://localhost:4848 and log in:

A connection factory can be added by expanding the Resources node in the tree at the left-hand side of the web console, expanding the JMS Resources node and clicking on the Connection Factories node, then clicking on the New... button in the main area of the web console.

For our purposes, we can take most of the defaults. The only thing we need to do is enter a Pool Nameand pick a Resource Type for our connection factory.

It is always a good idea to use a Pool Name starting with "jms/" when picking a name for JMS resources. This way JMS resources can be easily identified when browsing a JNDI tree.

In the text field labeled Pool Name, enter jms/GlassFishBookConnectionFactory. Our code examples later in this article will use this JNDI name to obtain a reference to this connection factory.

The Resource Type drop-down menu has three options:

• javax.jms.TopicConnectionFactory - used to create a connection factory that creates JMS topics for JMS clients using the pub/sub messaging domain
• javax.jms.QueueConnectionFactory - used to create a connection factory that creates JMS queues for JMS clients using the PTP messaging domain
• javax.jms.ConnectionFactory - used to create a connection factory that creates either JMS topics or JMS queues

For our example, we will select javax.jms.ConnectionFactory. This way we can use the same connection factory for all our examples, those using the PTP messaging domain and those using the pub/sub messaging domain.

After entering the Pool Name for our connection factory, selecting a connection factory type, and optionally entering a description for our connection factory, we must click on the OK button for the changes to take effect.

We should then see our newly created connection factory listed in the main area of the GlassFish web console.

Setting up a JMS message queue

A JMS message queue can be added by expanding the Resources node in the tree at the left-hand side of the web console, expanding the JMS Resources node and clicking on the Destination Resourcesnode, then clicking on the New... button in the main area of the web console.

In our example, the JNDI name of the message queue is jms/GlassFishBookQueue. The resource type for message queues must be javax.jms.Queue. Additionally, a Physical Destination Name must be entered. In this example, we use GlassFishBookQueue as the value for this field.

After clicking on the New... button, entering the appropriate information for our message queue, and clicking on the OK button, we should see the newly created queue:

Setting up a JMS message topic

Setting up a JMS message topic in GlassFish is very similar to setting up a message queue.

In the GlassFish web console, expand the Resources node in the tree at the left hand side, then expand the JMS Resouces node and click on the Destination Resources node, then click on the New... button in the main area of the web console.

Our examples will use a JNDI Name of jms/GlassFishBookTopic. As this is a message topic, Resource Type must be javax.jms.Topic. The Description field is optional. The Physical Destination Name property is required. For our example, we will use GlassFishBookTopic as the value for this property.

After clicking on the OK button, we can see our newly created message topic:

Now that we have set up a connection factory, a message queue, and a message topic, we are ready to start writing code using the JMS API.

Message queues

Like we mentioned earlier, message queues are used when our JMS code uses the point-to-point (PTP) messaging domain. For the PTP messaging domain, there is usually one message producer and one message consumer. The message producer and the message consumer don't need to run concurrently in order to communicate. The messages placed in the message queue by the message producer will stay in the message queue until the message consumer executes and requests the messages from the queue.

Sending messages to a message queue

The following example illustrates how to add messages to a message queue:

package net.ensode.glassfishbook;

import javax.annotation.Resource;
import javax.jms.Connection;
import javax.jms.ConnectionFactory;
import javax.jms.JMSException;
import javax.jms.MessageProducer;
import javax.jms.Queue;
import javax.jms.Session;
import javax.jms.TextMessage;

public class MessageSender
{
@Resource(mappedName = "jms/GlassFishBookConnectionFactory")
private static ConnectionFactory connectionFactory;
@Resource(mappedName = "jms/GlassFishBookQueue")
private static Queue queue;

public void produceMessages()
{
MessageProducer messageProducer;
TextMessage textMessage;
try
{
Connection connection = connectionFactory.createConnection();
Session session = connection.createSession(false,
Session.AUTO_ACKNOWLEDGE);
messageProducer = session.createProducer(queue);
textMessage = session.createTextMessage();

textMessage.setText("Testing, 1, 2, 3. Can you hear me?");
System.out.println("Sending the following message: "
+ textMessage.getText());
messageProducer.send(textMessage);

textMessage.setText("Do you copy?");
System.out.println("Sending the following message: "
+ textMessage.getText());
messageProducer.send(textMessage);
textMessage.setText("Good bye!");
System.out.println("Sending the following message: "
+ textMessage.getText());
messageProducer.send(textMessage);

messageProducer.close();
session.close();
connection.close();
}
catch (JMSException e)
{
e.printStackTrace();
}
}
public static void main(String[] args)
{
new MessageSender().produceMessages();
}
}

Before delving into the details of this code, alert readers might have noticed that this class is a standalone Java application as it contains a main method. As this class is standalone, it executes outside the application server. In spite of this, we can see that some resources are injected into it, specifically the connection factory and queue. The reason we can inject resources into this code, even though it runs outside the application server, is because GlassFish includes a utility called appclient.

This utility allows us to "wrap" an executable JAR file and allows it to have access to the application server resources. To execute the previous code, assuming it is packaged in an executable JAR file calledjmsptpproducer.jar, we would type the following command in the command line:

appclient -client jmsptpproducer.jar

We would then see, after some GlassFish log entries, the following output on the console:

Sending the following message: Testing, 1, 2, 3. Can you hear me?
Sending the following message: Do you copy?
Sending the following message: Good bye!

The appclient executable can be found under [GlassFish installation directory]/glassfish/bin. The previous example assumes this directory is in your PATH variable. If it isn't the complete path to the appclientexecutable, it must be typed in the command line.

With that out of the way, we can now explain the code.

The produceMessages() method performs all the necessary steps to send messages to a message queue.

The first thing this method does is obtain a JMS connection by invoking the createConnection() method on the injected instance of javax.jms. ConnectionFactory. Notice that the mappedName attribute of the@Resource annotation decorating the connection factory object matches the JNDI name of the connection factory we set up in the GlassFish web console. Behind the scenes, a JNDI lookup is made using this name to obtain the connection factory object.

After obtaining a connection, the next step is to obtain a JMS session from said connection. This can be accomplished by calling the createSession() method on the Connection object. As can be seen in the previous code, the createSession() method takes two parameters.

The first parameter of the createSession() method is a Boolean indicating if the session is transacted. If this value is true, several messages can be sent as part of a transaction by invoking the commit() method in the session object. Similarly, they can be rolled back by invoking its rollback() method .

The second parameter of the createSession() method indicates how messages are acknowledged by the message receiver. Valid values for this parameter are defined as constants in the javax.jms.Sessioninterface.

• Session.AUTO_ACKNOWLEDGE: indicates that the session will automatically acknowledge the receipt of a message.
• Session.CLIENT_ACKNOWLEDGE: indicates that the message receiver must explicitly call the acknowledge() method on the message.
• Session.DUPS_OK_ACKNOWLEDGE: indicates that the session will lazily acknowledge the receipt of messages. Using this value might result in some messages being delivered more than once.

After obtaining a JMS session, an instance of javax.jms.MessageProducer is obtained by invoking thecreateProducer() method on the session object. The MessageProducer object is the one that will actually send messages to the message queue. The injected Queue instance is passed as a parameter to thecreateProducer() method . Again, the value of the mappedName attribute for the @Resource annotation decorating this object must match the JNDI name we gave our message queue when setting it up in the GlassFish web console.

After obtaining an instance of MessageProducer, the code creates a series of text messages by invoking the createTextMessage() method on the session object. This method returns an instance of a class implementing the javax.jms.TextMessage interface. This interface defines a method called setText() , which is used to set the actual text in the message. After creating each text message and setting its text, they are sent to the queue by invoking the send() method on the MessageProducer object.

After sending the messages, the code disconnects from the JMS queue by invoking the close() method on the MessageProducer object , on the Session object , and on the Connection object.

Although the previous example sends only text messages to the queue, we are not limited to this type of message. The JMS API provides several types of messages that can be sent and received by JMS applications. All message types are defined as interfaces in the javax.jms package.

The following table lists all the available message types:

Message type	Description
BytesMessage	Allows sending an array of bytes as a message.
MapMessage	Allows sending an implementation of java.util.Map as a message.
ObjectMessage	Allows sending any Java object implementing java.io.Serializable as a message.
StreamMessage	Allows sending an array of bytes as a message. Differs from BytesMessage in that it stores the type of each primitive type added to the stream.
TextMessage	Allows sending a java.lang.String as a message.

For more information on all of these message types, consult their JavaDoc documentation athttp://java.sun.com/javaee/6/docs/api/.

Retrieving messages from a message queue

There is no point in sending messages from a queue if nothing is going to receive them. The following example illustrates how to retrieve messages from a JMS message queue:

package net.ensode.glassfishbook;

import javax.annotation.Resource;
import javax.jms.Connection;
import javax.jms.ConnectionFactory;
import javax.jms.JMSException;
import javax.jms.MessageConsumer;
import javax.jms.Queue;
import javax.jms.Session;
import javax.jms.TextMessage;

public class MessageReceiver
{
  @Resource(mappedName = "jms/GlassFishBookConnectionFactory")
  private static ConnectionFactory connectionFactory;
  @Resource(mappedName = "jms/GlassFishBookQueue")
  private static Queue queue;
  public void getMessages()
  {
    Connection connection;
    MessageConsumer messageConsumer;
    TextMessage textMessage;
    boolean goodByeReceived = false;
    try
    {
      connection = connectionFactory.createConnection();
      Session session = connection.createSession(false,
        Session.AUTO_ACKNOWLEDGE);
      messageConsumer = session.createConsumer(queue);
      connection.start();
      while (!goodByeReceived)
      {
        System.out.println("Waiting for messages...");
        textMessage = (TextMessage) messageConsumer.receive();
        if (textMessage != null)
        {
          System.out.print("Received the following message: ");
          System.out.println(textMessage.getText());
          System.out.println();
        }
        if (textMessage.getText() != null
          && textMessage.getText().equals("Good bye!"))
        {
          goodByeReceived = true;
        }
      }
      messageConsumer.close();
      session.close();
      connection.close();
    }
    catch (JMSException e)
    {
      e.printStackTrace();
    }
  }
  public static void main(String[] args)
  {
    new MessageReceiver().getMessages();
  }
}

Just like in the previous example, an instance of javax.jms.ConnectionFactory and an instance ofjavax.jms.Queue are injected by using the @Resource annotation. Getting a connection and a JMS session is exactly the same as in the previous example.

In this example, we obtain an instance of javax.jms.MessageConsumer by calling the createConsumer()method on the JMS session object. When we are ready to start receiving messages from the message queue, we need to invoke the start() method on the JMS connection object.

Code not receiving messages?
A common mistake when writing JMS messages is to fail to call the start() method on the JMS connection object. If our code is not receiving messages it should be receiving, we need to make sure we didn't forget to call this method.

Messages are received by invoking the receive() method on the instance of MessageConsumer obtained from the JMS session. This method returns an instance of a class implementing the javax.jms.Messageinterface. It must be casted to the appropriate type in order to obtain the actual message.

In this particular example, we placed this method call in a while loop, as we are expecting a message that will let us know that no more messages are coming. Specifically, we are looking for a message containing the text "Good bye!". Once we receive said message, we break out of the loop and continue processing. In this particular case, there is no more processing to do. Therefore, all we do is call theclose() method on the message consumer object, on the session object, and on the connection object.

Just like in the previous example, using the appclient utility allows us to inject resources into the code and prevents us from having to add any libraries to the CLASSPATH. After executing the code through theappclient utility, we should see the following output in the command line:

appclient -client target/jmsptpconsumer.jar
Waiting for messages...
Received the following message: Testing, 1, 2, 3. Can you hear me?
Waiting for messages...
Received the following message: Do you copy?
Waiting for messages...
Received the following message: Good bye!

This of course assumes that the previous example was already executed and it placed the messages in the message queue.

Asynchronously receiving messages from a message queue

The MessageConsumer.receive() method has a disadvantage—it blocks execution until a message is received from the queue. We can avoid this disadvantage by receiving messages asynchronously via an implementation of the javax.jms.MessageListener interface.

The javax.jms.MessageListener interface contains a single method called onMessage. It takes an instance of a class implementing the javax.jms.Message interface as its sole parameter. The following example illustrates a typical implementation of this interface:

package net.ensode.glassfishbook;

import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageListener;
import javax.jms.TextMessage;

public class ExampleMessageListener implements MessageListener
{
  @Override
  public void onMessage(Message message)
  {
    TextMessage textMessage = (TextMessage) message;
    try
    {
      System.out.print("Received the following message: ");
      System.out.println(textMessage.getText());
      System.out.println();
    }
    catch (JMSException e)
    {
      e.printStackTrace();
    }
  }
}

In this case, the onMessage() method simply outputs the message text to the console.

Our main code can now delegate message retrieval to our custom MessageListener implementation:

package net.ensode.glassfishbook;

import javax.annotation.Resource;
import javax.jms.Connection;
import javax.jms.ConnectionFactory;
import javax.jms.JMSException;
import javax.jms.MessageConsumer;
import javax.jms.Queue;
import javax.jms.Session;

public class AsynchMessReceiver
{
  @Resource(mappedName = "jms/GlassFishBookConnectionFactory")
  private static ConnectionFactory connectionFactory;
  @Resource(mappedName = "jms/GlassFishBookQueue")
  private static Queue queue;

  public void getMessages()
  {
    Connection connection;
    MessageConsumer messageConsumer;
    try
    {
      connection = connectionFactory.createConnection();
      Session session = connection.createSession(false,
        Session.AUTO_ACKNOWLEDGE);
      messageConsumer = session.createConsumer(queue);
      messageConsumer.setMessageListener(new
        ExampleMessageListener());
      connection.start();
  
      System.out.println("The above line wil l allow the "
          + "MessageListener implementation to "
          + "receiving and processing messages from the queue.");
      Thread.sleep(1000);
      System.out.println("Our code does not have to block "
          + "while messages are received.");
      Thread.sleep(1000);
      System.out.println("It can do other stuff "
          + "(hopefully something more useful than sending "
          + "silly output to the console. :)");
      Thread.sleep(1000);
      messageConsumer.close();
      session.close();
      connection.close();
    }
    catch (JMSException e)
    {
      e.printStackTrace();
    }
    catch (InterruptedException e)
    {
      e.printStackTrace();
    }
  }
  public static void main(String[] args)
  {
    new AsynchMessReceiver().getMessages();
  }
}

The only relevant difference between this example and the one in the previous section is that in this case, we are calling the setMessageListener() method on the instance of javax.jms.MessageConsumerobtained from the JMS session. We pass an instance of our custom implementation ofjavax.jms.MessageListener to this method. Its onMessage() method is automatically called whenever there is a message waiting in the queue. By using this approach, the main code does not block while waiting to receive messages.

Executing the previous example (using of course GlassFish's appclient utility) results in the following output:

appclient -client target/jmsptpasynchconsumer.jar
The above line will allow the MessageListener implementation to receiving
and processing messages from the queue.
Received the following message: Testing, 1, 2, 3. Can you hear me?

Received the following message: Do you copy?

Received the following message: Good bye!

Our code does not have to block while messages are received.
It can do other stuff (hopefully something more useful than sending silly
output to the console. :)

Notice how the messages were received and processed while the main thread was executing. We can tell this is the case because the output of the onMessage() method of our MessageListener can be seen between calls to System.out.println() in the primary class.

Browsing message queues

JMS provides a way to browse message queues without actually removing the messages from the queue. The following example illustrates how to do this:

package net.ensode.glassfishbook;

import java.util.Enumeration;

import javax.annotation.Resource;
import javax.jms.Connection;
import javax.jms.ConnectionFactory;
import javax.jms.JMSException;
import javax.jms.Queue;
import javax.jms.QueueBrowser;
import javax.jms.Session;
import javax.jms.TextMessage;

public class MessageQueueBrowser
{
@Resource(mappedName = "jms/GlassFishBookConnectionFactory")
private static ConnectionFactory connectionFactory;
@Resource(mappedName = "jms/GlassFishBookQueue")
private static Queue queue;

public void browseMessages()
{
try
{
Enumeration messageEnumeration;
TextMessage textMessage;
Connection connection = connectionFactory.createConnection();
Session session = connection.createSession(false,
Session.AUTO_ACKNOWLEDGE);
QueueBrowser browser = session.createBrowser(queue);
messageEnumeration = browser.getEnumeration();
if (messageEnumeration != null)
{
if (!messageEnumeration.hasMoreElements())
{
System.out.println("There are no messages " + "in the
queue.");
}
else
{
System.out.println("The following messages are in the
queue:");
while (messageEnumeration.hasMoreElements())
{
textMessage =
(TextMessage) messageEnumeration.nextElement();
System.out.println(textMessage.getText());
}
}
}
session.close();
connection.close();
}
catch (JMSException e)
{
e.printStackTrace();
}
}
public static void main(String[] args)
{
new MessageQueueBrowser().browseMessages();
}
}

As we can see, the procedure to browse messages in a message queue is straightforward. We obtain a JMS connection and a JMS session the usual way, then invoke the createBrowser() method on the JMS session object. This method returns an implementation of the javax.jms.QueueBrowser interface. This interface contains a getEnumeration() method that we can invoke to obtain an enumeration containing all messages in the queue. To examine the messages in the queue, we simply traverse this enumeration and obtain the messages one by one. In the previous example, we simply invoke the getText() method of each message in the queue.

Summary

In this article, we saw how to set up JMS connection factories, JMS message queues, and JMS message topics in GlassFish using the GlassFish web console. We also saw how to send and receive messages to and from a message queue.