6 Developing a Basic JMS Application

This chapter describes how to set up a basic WebLogic JMS application using the JMS 2.0 and JMS 1.1 APIs.

Importing Required Packages
Setting Up a JMS Application
Sending Messages
Receiving Messages
Acknowledging Received Messages
Releasing Object Resources

Importing Required Packages

The following table lists the packages that are commonly used by WebLogic JMS applications.

Table 6-1 WebLogic JMS Packages

Package	Description
javax.jms	JMS API. This package is always used by WebLogic JMS applications. See `http://docs.oracle.com/javaee/7/api/javax/jms/package-summary.html`.
javax.naming weblogic.jndi	JNDI packages required for server and destination lookups. See `http://docs.oracle.com/javase/7/docs/api/javax/naming/package-summary.html`.
javax.transaction.UserTransaction	JTA API required for JTA user transaction support. See `http://www.oracle.com/technetwork/java/javaee/jta/index.html`.
weblogic.jms.extensions	WebLogic-specific JMS public API that provides additional classes and methods, as described in Value-Added Public JMS API Extensions.

Setting Up a JMS Application

Before you can send and receive messages, you must set up a JMS application. The following sections describe the procedure to set up a basic WebLogic JMS application:

Using Simplified API to Set Up a JMS Application
Using Classic API to Set Up a JMS Application

You must ensure that the system administrator responsible for configuring WebLogic Server has configured the required JMS resources, including the connection factories, JMS servers, and destinations.

For information about JMS resource definitions, see "Configuring Basic JMS System Resources" in Administering JMS Resources for Oracle WebLogic Server.
For information about configuring other JMS resources, see "Configure Messaging" in the Oracle WebLogic Server Administration Console Online Help.
For more information about the JMS classes and methods described in these sections, see Understanding the JMS API, or the javax.jms, at http://docs.oracle.com/javaee/7/api/javax/jms/package-summary.html, or the weblogic.jms.extensions Javadoc in Java API Reference for Oracle WebLogic Server.
For information about setting up transacted applications and JTA user transactions, see Chapter 13, "Using Transactions with WebLogic JMS."

Using Simplified API to Set Up a JMS Application

Oracle WebLogic Server 12.2.1 supports the JMS 2.0 simplified API for sending and receiving messages. For more information about the simplified API, see Chapter 5, "Understanding the Simplified API Programming Model".

Figure 6-1 illustrates the steps required to set up a JMS application using JMS 2.0 Simplified API.

Figure 6-1 Setting up a JMS Application Using the Simplified API

Description of ''Figure 6-1 Setting up a JMS Application Using the Simplified API''

Look Up a Connection Factory in JNDI

Before you can look up a connection factory, it must be defined as part of the configuration information.

The administrator can configure new connection factories during configuration; however, these factories must be uniquely named or the server will not boot. You can also use the default connection factories defined by the Java EE specification and WebLogic Server. For information, see "Connection Factory Configuration" in Administering JMS Resources for Oracle WebLogic Server.

Once the connection factory has been defined, you can look it up by first establishing a JNDI context (namingContext) using the InitialContext() constructor, at http://docs.oracle.com/javase/7/docs/api/javax/naming/InitialContext.html#InitialContext(). For any application other than a servlet application, you must provide a Hashtable defining the environment when calling the InitialContext constructor.

Once the JNDI context is defined, to look up a connection factory in JNDI, execute the following command:

ConnectionFactory connectionFactory = 
 (ConnectionFactory) namingContext.lookup(CF_name);

The CF_name argument specifies the connection factory name defined during configuration.

For more information about the ConnectionFactory class, see ConnectionFactory, or the javax.jms.ConnectionFactory Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/ConnectionFactory.html.

Look Up a Queue or Topic

Before you can look up a queue or a topic, it must be configured by the WebLogic JMS system administrator, as described in "Configure topics" and "Configure queues" in the Oracle WebLogic Server Administration Console Online Help. For more information, see Destination or the Javadocs at http://docs.oracle.com/javaee/7/api/javax/jms/Queue.html and http://docs.oracle.com/javaee/7/api/javax/jms/Topic.html.

Once the destination has been configured, you can look up a destination using one of the following procedures:

You can look up a queue or topic destination by establishing a JNDI context (namingContext), which has already been accomplished in Look Up a Connection Factory in JNDI, and executing one of the following commands, for Point-to-Point or Publish/Subscribe messaging, respectively:

Queue queue = (Queue) namingContext.lookup(Queue_name); 

Topic topic = (Topic) namingContext.lookup(Topic_name);

The Queue_name and Topic_name arguments specify the JNDI names of the queue and topic destinations defined during configuration.

Create a JMSContext Object

A JMSContext object replaces the Connection and Session objects in the classic API. For more information, see New Interfaces in the Simplified JMS API.

The JMSContext object can be created by calling one of the several createContext methods on a ConnectionFactory object. For example:

JMSContext context = connectionFactory.createContext(sessionMode);

In this case, a connection and a session with the specified mode are created for use by the new JMSContext object context. For more information, see connectionFactory interface definition in http://docs.oracle.com/javaee/7/api/javax/jms/ConnectionFactory.html.

Alternatively, you can inject JMSContext in the Java EE web and EJB containers using the @Inject annotation as described in Declaring a JMSContext Object using @Inject Annotation. This is the recommended way for creating JMSContext in Java EE applications. For example:

@Inject @JMSConnectionFactory("myJMSCF") JMSContext context;

For more information about using the JMSContext interface, see http://docs.oracle.com/javaee/7/api/javax/jms/JMSContext.html.

Create JMSProducer and JMSConsumer Objects

Use the JMSProducer and JMSConsumer objects to send and receive messages respectively.

You can create a JMSProducer object by calling the createProducer method on a JMSContext object as follows:

JMSProducer producer = context.createProducer();

Note:

You need not save the JMSProducer object in a variable. Instead, create the object while calling the send method as follows:

context.createProducer().send(queue, message);

For more information, see http://docs.oracle.com/javaee/7/api/javax/jms/JMSProducer.html.

You can create a JMSConsumer object by passing a Queue or Topic object to one of the createConsumer methods on a JMSContext object as follows:

JMSContext context = connectionFactory.createContext();
JMSConsumer consumer = context.createConsumer(queue);

For more information, see http://docs.oracle.com/javaee/7/api/javax/jms/JMSPConsumer.html.

Sending and Receiving Messages using the Simplified API

The following sections describe how to send and receive messages using the Simplified API:

Sending Messages Using the Simplified JMS API
Sending a Message Asynchronously
Receive Messages Asynchronously using the Simplified API
Receive Messages Synchronously using the Simplified API

Using Classic API to Set Up a JMS Application

The following figure illustrates the steps required to set up a JMS application using JMS 1.1 Classic API.

Figure 6-2 Setting Up a JMS Application using Classic API

Description of ''Figure 6-2 Setting Up a JMS Application using Classic API''

Note:

Oracle WebLogic Server 12.2.1 supports JMS 2.0 simplified API for sending and receiving messages. See Understanding the Simplified API Programming Model.

Step 1: Look Up a Connection Factory in JNDI

Before you can look up a connection factory, it must be defined as part of the configuration information.

Once the connection factory has been defined, you can look it up by first establishing a JNDI context (context) using the InitialContext() method, at http://docs.oracle.com/javase/7/docs/api/javax/naming/InitialContext.html#InitialContext(). For any application other than a servlet application, you must pass an environment used to create the initial context.

Once the context is defined, to look up a connection factory in JNDI, execute one of the following commands, for PTP or Pub/Sub messaging, respectively:

QueueConnectionFactory queueConnectionFactory = 
 (QueueConnectionFactory) context.lookup(CF_name);

TopicConnectionFactory topicConnectionFactory = 
 (TopicConnectionFactory) context.lookup(CF_name);

The CF_name argument specifies the connection factory name defined during configuration.

Step 2: Create a Connection Using the Connection Factory

You can create a connection for accessing the messaging system by using the ConnectionFactory methods described in the following sections.

For more information about the Connection class, see Connection, or the javax.jms.Connection Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/Connection.html.

Create a Queue Connection

The QueueConnectionFactory provides the following two methods for creating a queue connection:

public QueueConnection createQueueConnection(
) throws JMSException

public QueueConnection createQueueConnection(
 String userName,
 String password
) throws JMSException

The first method creates a QueueConnection; the second method creates a QueueConnection using a specified user identity. In each case, a connection is created in stopped mode and must be started in order to accept messages, as described in Step 7: Start the Connection.

For more information about the QueueConnectionFactory class methods, see the javax.jms.QueueConnectionFactory Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/QueueConnectionFactory.html. For more information about the QueueConnection class, see the javax.jms.QueueConnection Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/QueueConnection.html.

Create a Topic Connection

The TopicConnectionFactory provides the following two methods for creating a topic connection:

public TopicConnection createTopicConnection(
) throws JMSException

public TopicConnection createTopicConnection(
 String userName,
 String password
) throws JMSException

The first method creates a TopicConnection; the second method creates a TopicConnection using a specified user identity. In each case, a connection is created in stopped mode and must be started in order to accept messages, as described in Step 7: Start the Connection.

For more information about the TopicConnectionFactory class methods, see the javax.jms.TopicConnectionFactory Javadoc., at http://docs.oracle.com/javaee/7/api/javax/jms/TopicConnectionFactory.html. For more information about the TopicConnection class, see the javax.jms.TopicConnection Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/TopicConnection.html.

Step 3: Create a Session Using the Connection

You can create one or more sessions for accessing a queue or topic using the Connection methods described in the following sections.

Note:

A session and its message producers and consumers can only be accessed by one thread at a time. Their behavior is undefined if multiple threads access them simultaneously.

WebLogic JMS does not support having both types of MessageConsumer (QueueConsumer and TopicSubscriber) for a single Session. However, it does support a single session with both a QueueSender and a TopicSubscriber (and vice-versa: QueueConsumer and TopicPublisher), or with multiple MessageProducers of any type.

For more information about the Session class, see Session or the javax.jms.Session Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/Session.html.

Create a Session using the createSession Method

Use the createSession method in javax.jms.Connection to create a session. This method accepts a single parameter, sessionMode, or no parameter as follows:

Session createSession(int sessionMode) throws JMSException

or

Session createSession() throws JMSException

Create a Queue Session

The QueueConnection class defines the following method for creating a queue session:

public QueueSession createQueueSession(
 boolean transacted,
 int acknowledgeMode
) throws JMSException

You must specify a boolean argument indicating whether the session will be transacted (true) or non-transacted (false), and an integer that indicates the acknowledge mode for non-transacted sessions. The acknowledgeMode attribute is ignored for transacted sessions. In this case, messages are acknowledged when the transaction is committed using the commit() method.

For more information about the QueueConnection class methods, see the javax.jms.QueueConnection Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/QueueConnection.html. For more information about the QueueSession class, see the javax.jms.QueueSession Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/QueueSession.html.

Create a Topic Session

The TopicConnection class defines the following method for creating a topic session:

public TopicSession createTopicSession(
 boolean transacted,
 int acknowledgeMode
) throws JMSException

For more information about the TopicConnection class methods, see the javax.jms.TopicConnection Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/TopicConnection.html. For more information about the TopicSession class, see the javax.jms.TopicSession Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/TopicSession.html.

Step 4: Look Up a Destination (Queue or Topic)

Before you can look up a destination, the destination must be configured by the WebLogic JMS system administrator, as described in "Configure topics" and "Configure queues" in the Oracle WebLogic Server Administration Console Online Help. For more information about the Destination class, see Destination or the javax.jms.Destination Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/Destination.html.

Once the destination has been configured, you can look up a destination using one of the following procedures:

Using a JNDI Name

You can look up a destination by establishing a JNDI context (context), which has already been accomplished in Look Up a Connection Factory in JNDI, and executing one of the following commands, for PTP or Pub/Sub messaging, respectively:

Queue queue = (Queue) context.lookup(Dest_name);

Topic topic = (Topic) context.lookup(Dest_name);

The Dest_name argument specifies the JNDI name of the destination defined during configuration.

Use a Reference

If you do not use a JNDI namespace, you can use the following QueueSession or TopicSession method to reference a queue or topic, respectively:

Note:

The createQueue() and createTopic() methods do not create destinations dynamically; they create only references to destinations that already exist. For information about creating destinations dynamically, see Chapter 8, "Using JMS Module Helper to Manage Applications."

public Queue createQueue(
 String queueName
) throws JMSException

public Topic createTopic(
 String topicName
) throws JMSException

For the syntax of JNDI name, createQueue(), and createTopic(), see How to Lookup a Destination.

Step 5: Create Message Producers and Message Consumers

You can create message producers and message consumers by passing the destination reference to the Session methods described in the following sections.

Note:

Each consumer receives its own local copy of a message. Once received, you can modify the header field values; however, the message properties and message body are read only. (Attempting to modify the message properties or body at this point will generate a MessageNotWriteableException.) You can modify the message body by executing the corresponding message type's clearbody() method to clear the existing contents and enable write permission.

For more information about the MessageProducer and MessageConsumer classes, see MessageProducer and MessageConsumer, or the javax.jms.MessageProducer, at http://docs.oracle.com/javaee/7/api/javax/jms/MessageProducer.html, and javax.jms.MessageConsumer Javadocs, at http://docs.oracle.com/javaee/7/api/javax/jms/MessageConsumer.html.

Create QueueSenders and QueueReceivers

The QueueSession object defines the following methods for creating queue senders and receivers:

public QueueSender createSender(
 Queue queue
) throws JMSException

public QueueReceiver createReceiver(
 Queue queue
) throws JMSException

public QueueReceiver createReceiver(
 Queue queue, 
 String messageSelector
) throws JMSException

You must specify the queue object for the queue sender or receiver being created. You may also specify a message selector for filtering messages. Message selectors are described in more detail in Filtering Messages.

If you pass a value of null to the createSender() method, you create an anonymous producer. In this case, you must specify the queue name when sending messages, as described in Sending Messages.

Once the queue sender or receiver has been created, you can access the queue name associated with the queue sender or receiver using the following QueueSender or QueueReceiver method:

public Queue getQueue(
) throws JMSException

For more information about the QueueSession class methods, see the javax.jms.QueueSession Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/QueueSession.html. For more information about the QueueSender and QueueReceiver classes, see the javax.jms.QueueSender, at http://docs.oracle.com/javaee/7/api/javax/jms/QueueSender.html, and javax.jms.QueueReceiver Javadocs, at http://docs.oracle.com/javaee/7/api/javax/jms/QueueReceiver.html.

Create TopicPublishers and TopicSubscribers

The TopicSession object defines the following methods for creating topic publishers and topic subscribers:

public TopicPublisher createPublisher(
 Topic topic
) throws JMSException

public TopicSubscriber createSubscriber(
 Topic topic
) throws JMSException

public TopicSubscriber createSubscriber(
 Topic topic, 
 String messageSelector, 
 boolean noLocal
) throws JMSException

Note:

The methods described in this section create non-durable subscribers. Non-durable topic subscribers only receive messages sent while they are active. For information about the methods used to create durable subscriptions enabling messages to be retained until all messages are delivered to a durable subscriber, see Creating Subscribers for a Durable Subscription. In this case, durable subscribers only receive messages that are published after the subscriber has subscribed.

You must specify the topic object for the publisher or subscriber being created. You may also specify a message selector for filtering messages and a noLocal flag (described later in this section). Message selectors are described in more detail in Filtering Messages.

If you pass a value of null to the createPublisher() method, you create an anonymous producer. In this case, you must specify the topic name when sending messages, as described in Sending Messages.

An application can have JMS connections that it uses to both publish and subscribe to the same topic. Because topic messages are delivered to all subscribers, the application can receive messages it has published itself. To prevent this behavior, a JMS application can set a noLocal flag to true.

Once the topic publisher or subscriber has been created, you can access the topic name associated with the topic publisher or subscriber using the following TopicPublisher or TopicSubscriber method:

Topic getTopic(
) throws JMSException

In addition, you can access the noLocal variable setting associated with the topic subscriber using the following TopicSubscriber method:

boolean getNoLocal(
) throws JMSException

For more information about the TopicSession class methods, see the javax.jms.TopicSession Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/TopicSession.html. For more information about the TopicPublisher and TopicSubscriber classes, see the javax.jms.TopicPublisher, at http://docs.oracle.com/javaee/7/api/javax/jms/TopicPublisher.html, and javax.jms.TopicSubscriber Javadocs, at http://docs.oracle.com/javaee/7/api/javax/jms/TopicSubscriber.html.

Step 6a: Create the Message Object (Message Producers)

Note:

This step applies to message producers only.

To create the message object, use one of the following Session or WLSession class methods:

Session Methods

Note:

These methods are inherited by both the QueueSession and TopicSession subclasses.

public BytesMessage createBytesMessage(
) throws JMSException

public MapMessage createMapMessage(
) throws JMSException

public Message createMessage(
) throws JMSException

public ObjectMessage createObjectMessage(
) throws JMSException

public ObjectMessage createObjectMessage(
 Serializable object
) throws JMSException

public StreamMessage createStreamMessage(
) throws JMSException

public TextMessage createTextMessage(
) throws JMSException

public TextMessage createTextMessage(
 String text
) throws JMSException

WLSession Method

public XMLMessage createXMLMessage(
 String text
) throws JMSException

For more information about the Session and WLSession class methods, see the javax.jms.Session, at http://docs.oracle.com/javaee/7/api/javax/jms/Session.html, and weblogic.jms.extensions.WLSession Javadocs, respectively. For more information about the Message class and its methods, see Message, or the javax.jms.Message Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/Message.html.

Step 6b: Optionally Register an Asynchronous Message Listener

Note:

This step applies to message consumers only.

To receive messages asynchronously, you must register an asynchronous message listener by performing the following steps:

Implement the javax.jms.MessageListener interface, at http://docs.oracle.com/javaee/7/api/javax/jms/MessageListener.html, which includes an onMessage() method.

Note:
For an example of the onMessage() method interface, see Example: Setting Up a Point-To-Point JMS Application Using Classic API.
If you wish to issue the close() method within an onMessage() method call, the system administrator must select the Allow Close In OnMessage option when configuring the connection factory. For more information on configuring connection factory options, see "Configuring Basic JMS System Resources" in Administering JMS Resources for Oracle WebLogic Server.
Set the message listener using the following MessageConsumer method, passing the listener information as an argument:
```
public void setMessageListener(
 MessageListener listener
) throws JMSException
```
Optionally, implement an exception listener on the session to catch exceptions, as described in Defining a Connection Exception Listener.

You can unset a message listener by calling the MessageListener() method with a value of null.

Once a message listener has been defined, you can access it by calling the following MessageConsumer method:

public MessageListener getMessageListener(
) throws JMSException

Note:

WebLogic JMS guarantees that multiple onMessage() calls for the same session will not be executed simultaneously.

If a message consumer is closed by an administrator or as the result of a server failure, a ConsumerClosedException is delivered to the session exception listener, if one has been defined. In this way, a new message consumer can be created, if necessary. For information about defining a session exception listener, see Defining a Connection Exception Listener.

The MessageConsumer class methods are inherited by the QueueReceiver and TopicSubscriber classes. For additional information about the MessageConsumer class methods, see MessageProducer and MessageConsumer or the javax.jms.MessageConsumer Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/MessageConsumer.html.

Step 7: Start the Connection

You start the connection using the Connection class start() method.

For additional information about starting, stopping, and closing a connection, see Starting, Stopping, and Closing a Connection or the javax.jms.Connection Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/Connection.html.

Example: Setting Up a Point-To-Point JMS Application Using Classic API

The following example is excerpted from the examples.jms.queue.QueueSend example, provided with WebLogic Server in the EXAMPLES_HOME\wlserver\samples\server\examples\src\examples\jms\classicapi\queue directory, where EXAMPLES_HOME represents the directory in which the WebLogic Server code examples are configured. The init() method shows how to set up and start a QueueSession for a JMS application. The following shows the init() method, with comments describing each setup step.

Define the required variables, including the JNDI context, JMS connection factory, and queue static variables.

public final static String JNDI_FACTORY=
       "weblogic.jndi.WLInitialContextFactory";
public final static String JMS_FACTORY=
       "weblogic.examples.jms.QueueConnectionFactory";
public final static String 
        QUEUE="weblogic.examples.jms.exampleQueue";

private QueueConnectionFactory qconFactory;
private QueueConnection qcon;
private QueueSession qsession;
private QueueSender qsender;
private Queue queue;
private TextMessage msg;

Set up the JNDI initial context, as follows:

InitialContext ic = getInitialContext(args[0]);
       .
       .
       .
private static InitialContext getInitialContext(
 String url
) throws NamingException
{
 Hashtable env = new Hashtable();
 env.put(Context.INITIAL_CONTEXT_FACTORY, JNDI_FACTORY);
 env.put(Context.PROVIDER_URL, url);
 return new InitialContext(env);
}

Note:

When setting up the JNDI initial context for an EJB or servlet, use the following method:

Context ctx = new InitialContext();

Create all the necessary objects for sending messages to a JMS queue. The ctx object is the JNDI initial context passed in by the main() method.

public void init(
 Context ctx, 
 String queueName
) throws NamingException, JMSException
{

Step 1

Look up a connection factory in JNDI.

 qconFactory = (QueueConnectionFactory) ctx.lookup(JMS_FACTORY);

Step 2

Create a connection using the connection factory.

 qcon = qconFactory.createQueueConnection();

Step 3

Create a session using the connection. The following code defines the session as non-transacted and specifies that messages will be acknowledged automatically. For more information about transacted sessions and acknowledge modes, see Session.

 qsession = qcon.createQueueSession(false,
 Session.AUTO_ACKNOWLEDGE);

Step 4

Look up a destination (queue) in JNDI.

 queue = (Queue) ctx.lookup(queueName);

Step 5

Create a reference to a message producer (queue sender) using the session and destination (queue).

 qsender = qsession.createSender(queue);

Step 6

Create the message object.

 msg = qsession.createTextMessage();

Step 7

Start the connection.

 qcon.start();
}

The init() method for the examples.jms.queue.QueueReceive example is similar to the QueueSend init() method shown previously, with the one exception. Steps 5 and 6 would be replaced by the following code, respectively:

qreceiver = qsession.createReceiver(queue);
qreceiver.setMessageListener(this);

In the first line, instead of calling the createSender() method to create a reference to the queue sender, the application calls the createReceiver() method to create the queue receiver.

In the second line, the message consumer registers an asynchronous message listener.

When a message is delivered to the queue session, it is passed to the examples.jms.QueueReceive.onMessage() method. The following code excerpt shows the onMessage() interface from the QueueReceive example:

public void onMessage(Message msg)
{
 try {
       String msgText;
       if (msg instanceof TextMessage) {
          msgText = ((TextMessage)msg).getText();
       } else { // If it is not a TextMessage...
        msgText = msg.toString();
       }

       System.out.println("Message Received: "+ msgText );

       if (msgText.equalsIgnoreCase("quit")) {
         synchronized(this) {

                quit = true;
              this.notifyAll(); // Notify main thread to quit
         }
       }
  } catch (JMSException jmse) {
   jmse.printStackTrace();
  }
}

The onMessage() method processes messages received through the queue receiver. The method verifies that the message is a TextMessage and, if it is, prints the text of the message. If onMessage() receives a different message type, it uses the message's toString() method to display the message contents.

Note:

It is good practice to verify that the received message is the type expected by the handler method.

For more information about the JMS classes used in this example, see Understanding the JMS API or the javax.jms Javadoc, at http://www.oracle.com/technetwork/java/jms/index.html.

Example: Setting Up a Publish-Subscribe JMS Application Using Classic API

The following example is excerpted from the examples.jms.topic.TopicSend example, provided with WebLogic Server in the EXAMPLES_HOME\wlserver\samples\server\examples\src\examples\jms\classicapi\topic directory, where EXAMPLES_HOME represents the directory in which the WebLogic Server code examples are configured. The init() method shows how to set up and start a topic session for a JMS application. The following shows the init() method, with comments describing each setup step.

Define the required variables, including the JNDI context, JMS connection factory, and topic static variables.

public final static String JNDI_FACTORY=
       "weblogic.jndi.WLInitialContextFactory";
public final static String JMS_FACTORY=
       "weblogic.examples.jms.TopicConnectionFactory";
public final static String 
       TOPIC="weblogic.examples.jms.exampleTopic";

protected TopicConnectionFactory tconFactory;
protected TopicConnection tcon;
protected TopicSession tsession;
protected TopicPublisher tpublisher;
protected Topic topic;
protected TextMessage msg;

Set up the JNDI initial context, as follows:

InitialContext ic = getInitialContext(args[0]);
       .
       .
       .
private static InitialContext getInitialContext(
 String url
) throws NamingException
{
  Hashtable env = new Hashtable();
  env.put(Context.INITIAL_CONTEXT_FACTORY, JNDI_FACTORY);
  env.put(Context.PROVIDER_URL, url);
  return new InitialContext(env);
}

Note:

When setting up the JNDI initial context for a servlet, use the following method:

Context ctx = new InitialContext();

Create all the necessary objects for sending messages to a JMS queue. The ctx object is the JNDI initial context passed in by the main() method.

public void init(
 Context ctx, 
 String topicName
) throws NamingException, JMSException
{

Step 1

Look up a connection factory using JNDI.

  tconFactory = 
   (TopicConnectionFactory) ctx.lookup(JMS_FACTORY);

Step 2

Create a connection using the connection factory.

  tcon = tconFactory.createTopicConnection();

Step 3

Create a session using the connection. The following defines the session as non-transacted and specifies that messages will be acknowledged automatically. For more information about setting session transaction and acknowledge modes, see Session.

  tsession = tcon.createTopicSession(false,
   Session.AUTO_ACKNOWLEDGE);

Step 4

Look up the destination (topic) using JNDI.

  topic = (Topic) ctx.lookup(topicName);

Step 5

Create a reference to a message producer (topic publisher) using the session and destination (topic).

  tpublisher = tsession.createPublisher(topic);

Step 6

Create the message object.

  msg = tsession.createTextMessage();

Step 7

Start the connection.

  tcon.start();
 }

The init() method for the examples.jms.topic.TopicReceive example is similar to the TopicSend init() method shown previously with on exception. Steps 5 and 6 would be replaced by the following code, respectively:

tsubscriber = tsession.createSubscriber(topic);
tsubscriber.setMessageListener(this);

In the first line, instead of calling the createPublisher() method to create a reference to the topic publisher, the application calls the createSubscriber() method to create the topic subscriber.

In the second line, the message consumer registers an asynchronous message listener.

When a message is delivered to the topic session, it is passed to the examples.jms.TopicSubscribe.onMessage() method. The onMessage() interface for the TopicReceive example is the same as the QueueReceive onMessage() interface, as described in Example: Setting Up a Point-To-Point JMS Application Using Classic API.

For more information about the JMS classes used in this example, see Understanding the JMS API or the javax.jms Javadoc, at http://www.oracle.com/technetwork/java/jms/index.html.

Sending Messages

Once you have set up the JMS application as described in Setting Up a JMS Application, you can send messages. To send a message, you can use either the simplified API or the classic API as described in the following sections:

Sending Messages Using the Simplified JMS API
Sending Messages Using the Classic JMS API

Sending Messages Using the Simplified JMS API

In simplified API, messages are sent by creating a JMSProducer object on behalf of JMSContext. For more information, see Create JMSProducer and JMSConsumer Objects.

To send a message to a specified destination, you can use the following JMSProducer method which is analogous to the send method of MessageProducer in the classic API:

JMSProducer send(Destination destination, Message message)

For example,

context.createProducer().send(destination,"Hello");

creates a TextMessage object and sets its body to "Hello", and then sends it to the specified destination.

You can also use the following JMSProducer methods, which create a message automatically for of the appropriate message type and set the payload to the specified parameter:

JMSProducer send(Destination destination,byte[] body)

JMSProducer send(Destination destination, Map<String,Object> body)

JMSProducer send(Destination destination, Serializable body)

JMSProducer send(Destination destination, String body)

For more information about the JMSProducer interface and send methods, see the Javadoc at:

http://docs.oracle.com/javaee/7/api/javax/jms/JMSProducer.html

WebLogic JMS provides proprietary attributes that you can use while sending messages. You can specify the delivery mode (DeliveryMode.PERSISTENT or DeliveryMode.NON_PERSISTENT), priority (0-9), delivery delay, and time-to-live (in milliseconds) by casting the JMSProducer instance to weblogic.jms.extensions.WLJMSProducer. See the Javadoc for WLSJMSProducer in Java API Reference for Oracle WebLogic Server.

For example,

context.createProducer().setDeliveryMode(DeliveryMode.NON_PERSISTENT).send(destination,message);

If not specified, the delivery mode, priority, and time-to-live attributes are set to one of the following:

Connection factory or destination override configuration attributes defined for the producer, as described "Configure default delivery parameters" in the Oracle WebLogic Server Administration Console Online Help.
Values specified using the JMSProducer object's set methods, as described in Setting JMSProducer and MessageProducer Attributes.

Sending Messages Using the Classic JMS API

Once you have set up the JMS application as described in Using Classic API to Set Up a JMS Application, you can send messages. To send a message, you must, in order, perform the steps described in the following sections:

Create a Message Object
Define a Message
Send the Message to a Destination Using MessageProducer

For more information about the JMS classes for sending messages and the message types, see the javax.jms.Message Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/Message.html. For information about receiving messages, see Receiving Messages.

Create a Message Object

This step has already been accomplished as part of the client setup procedure, as described in Step 6a: Create the Message Object (Message Producers).

Define a Message

This step may have been accomplished when setting up an application, as described in Step 6a: Create the Message Object (Message Producers). Whether or not this step has already been accomplished depends on the method that was called to create the message object. For example, for TextMessage and ObjectMessage types, when you create a message object, you have the option of defining the message when you create the message object.

If a value has been specified and you do not wish to change it, you can proceed to step 3.

If a value has not been specified or if you wish to change an existing value, you can define a value using the appropriate set method. For example, the method for defining the text of a TextMessage is as follows:

public void setText(
 String string
) throws JMSException

Note:

Messages can be defined as null.

Subsequently, you can clear the message body using the following method:

public void clearBody(
) throws JMSException

For more information about the methods used to define messages, see the javax.jms.Session Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/Session.html.

Send the Message to a Destination Using MessageProducer

The Destination and MessageProducer objects were created when you set up the application, as described in Using Classic API to Set Up a JMS Application.

Note:

If multiple topic subscribers are defined for the same topic, each subscriber will receive its own local copy of a message. Once received, you can modify the header field values; however, the message properties and message body are read only. You can modify the message body by executing the corresponding message type's clearbody() method to clear the existing contents and enable write permission.

For more information about the MessageProducer class, see MessageProducer and MessageConsumer or the javax.jms.MessageProducer Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/MessageProducer.html.

You must specify a message. You may also specify the queue name (for anonymous message producers), delivery mode (DeliveryMode.PERSISTENT or DeliveryMode.NON_PERSISTENT), priority (0-9), delivery delay, and time-to-live (in milliseconds). If not specified, the delivery mode, priority, and time-to-live attributes are set to one of the following:

Connection factory or destination override configuration attributes defined for the producer, as described "Configure default delivery parameters" in the Oracle WebLogic Server Administration Console Online Help.
Values specified using the message producer's set methods, as described in Setting JMSProducer and MessageProducer Attributes.

If you define the delivery mode as PERSISTENT, you should configure a backing store for the destination, as described in "Configure persistent stores" in the Oracle WebLogic Server Administration Console Online Help.

Note:

If no backing store is configured, then the delivery mode is changed to NON_PERSISTENT and messages are not written to the persistent store.

For more information about using the QueueSender and TopicPublisher methods for sending messages, see the WebLogic Server documentation at:

https://docs.oracle.com/middleware/1213/wls/JMSPG/implement.htm#JMSPG228

For additional information about the QueueSender class methods, see the javax.jms.QueueSender Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/QueueSender.html.

For more information about the TopicPublisher class methods, see the javax.jms.TopicPublisher Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/TopicPublisher.html.

Sending a Message Asynchronously

In asynchronous mode, the JMS client sends a message and returns control to the application without waiting for an acknowledgement from the JMS server.

To send messages asynchronously, your application should define a CompletionListener object. When an acknowledgement is received from the JMS server to indicate that the message has been received, the JMS provider notifies the application by invoking the callback method onCompletion on the CompletionListener object defined by the application. For more information about the CompletionListener interface, see http://docs.oracle.com/javaee/7/api/javax/jms/CompletionListener.html.

After defining the javax.jms.CompletionListener object, send messages asynchronously using the JMSProducer or MessageProducer objects as described below:

If you are using JMSProducer objects to send messages, call the method setAsync(CompletionListener listener) with a non-null CompletionListener on the JMSProducer object before calling the send method as listed in the following example:
```
// send a message asynchronously
try (JMSContext context = connectionFactory.createContext()) {
 MyCompletionListener myCompletionListener = new MyCompletionListener();
//call normal send method
 context.createProducer().setAsync(myCompletionListener).send(queue, "Hello world");
 ...
}
```
For more information, see Sending Messages Using the Simplified JMS API.
If you are using a MessageProducer to send messages, use the following method to send messages asynchronously:
```
messageProducer.send(message,completionListener);
```
For more information, see Sending Messages Using the Classic JMS API.

Setting JMSProducer and MessageProducer Attributes

As described in the previous section, when sending a message, you can optionally specify the delivery mode, priority, delivery delay, and time-to-live values. If not specified, these attributes are set to the connection factory configuration attributes, as described in "Configure connection factories" in the Oracle WebLogic Server Administration Console Online Help.

Alternatively, you can set the delivery mode, priority, time-to-deliver, time-to-live, and redelivery delay (timeout), and redelivery limit values dynamically using the message producer's set methods. The following table lists the message producer set and get methods for each dynamically configurable attribute.

Note:

The delivery mode, priority, time-to-live, time-to-deliver, redelivery delay (timeout), and redelivery limit attribute settings can be overridden by the destination using the Delivery Mode Override, Priority Override, Time To Live Override, Time To Deliver Override, Redelivery Delay Override, and Redelivery Limit configuration attributes, as described in "Configure message delivery overrides" and "Configure topic message delivery overrides" in the Oracle WebLogic Server Administration Console Online Help.

Table 6-2 Message Producer Set and Get Methods

Attribute	Set Method	Get Method
Delivery Mode	public void setDeliveryMode( int deliveryMode ) throws JMSException	public int getDeliveryMode( ) throws JMSException
Priority	public void setPriority( int defaultPriority ) throws JMSException	public int getPriority( ) throws JMSException
Time-To-Live	public void setTimeToLive( long timeToLive ) throws JMSException	public long getTimeToLive( ) throws JMSException
Redelivery Limit	public void setRedeliveryLimit( int redeliveryLimit ) throws JMSException	public int getredeliveryLimit( ) throws JMSException
Send Timeout	public void setsendTimeout( long sendTimeout ) throws JMSException	public long getsendTimeout( ) throws JMSException

Note:

JMS defines optional MessageProducer methods for disabling the message ID and timestamp information. However, these methods are ignored by WebLogic JMS.

For more information about the MessageProducer class methods, see the javax.jms.MessageProducer Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/MessageProducer.html, or the weblogic.jms.extensions.WLMessageProducer Javadoc.

Example: Sending Messages Within a PTP Application

The following example is excerpted from the examples.jms.queue.QueueSend example, provided with WebLogic Server in the EXAMPLES_HOME\wl_server\examples\src\examples\jms\queue directory, where EXAMPLES_HOME represents the directory in which the WebLogic Server code examples are configured. The example shows the code required to create a TextMessage, set the text of the message, and send the message to a queue.

msg = qsession.createTextMessage();
       .
       .
       .
public void send(
 String message
) throws JMSException
{
 msg.setText(message);
 qsender.send(msg);
}

For more information about the QueueSender class and methods, see the javax.jms.QueueSender Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/QueueSender.html.

Example: Sending Messages Within a Pub/Sub Application

The following example is excerpted from the examples.jms.topic.TopicSend example, provided with WebLogic Server in the EXAMPLES_HOME\wl_server\examples\src\examples\jms\topic directory, where EXAMPLES_HOME represents the directory in which the WebLogic Server code examples are configured. It shows the code required to create a TextMessage, set the text of the message, and send the message to a topic.

msg = tsession.createTextMessage();
       .
       .
       .
public void send(
 String message
) throws JMSException
{
 msg.setText(message);
 tpublisher.publish(msg);
}

For more information about the TopicPublisher class and methods, see the javax.jms.TopicPublisher Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/TopicPublisher.html.

Receiving Messages

Once you have set up the JMS application as described in Setting Up a JMS Application, you can receive messages.

To receive a message, you must create the receiver object and specify whether you want to receive messages asynchronously or synchronously.

This section describes how to receive messages using the JMSConsumer and MessageConsumer methods.

The order in which messages are received can be controlled by the following:

Message delivery attributes (delivery mode and sorting criteria) defined during configuration or as part of the send() method, as described in Sending Messages.
Destination sort order set using destination keys, as described in "Configure destination keys" in the Oracle WebLogic Server Administration Console Online Help.

Once received, you can modify the header field values; however, the message properties and message body are read-only. You can modify the message body by executing the corresponding message type's clearbody() method to clear the existing contents and enable write permission.

For more information about the JMS classes for receiving messages and the message types, see the javax.jms.Message Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/Message.html. For information about sending messages, see Sending Messages.

Receive Messages Asynchronously using the Simplified API

To receive messages, you must first create a JMSConsumer object using one of the several createConsumer or createDurableConsumer methods on JMSContext object.

Create a JMSConsumer object and use the method setMessageListener to specify the object that implements the MessageListener interface. Message delivery is started automatically.

JMSConsumer consumer = context.createConsumer(queue);
consumer.setMessageListener(messageListener);

Receiving Messages Asynchronously using the Classic API

This procedure is described within the context of setting up the application. For more information, see Step 6b: Optionally Register an Asynchronous Message Listener.

Note:

You can control the maximum number of messages that may exist for an asynchronous consumer and that have not yet been passed to the message listener by setting the Messages Maximum attribute when configuring the connection factory.

Asynchronous Message Pipeline

If messages are produced faster than asynchronous message listeners (consumers) can consume them, a JMS server will push multiple unconsumed messages in a batch to another session with available asynchronous message listeners. These in-flight messages are sometimes referred to as the message pipeline, or in some JMS vendors as the message backlog. The pipeline or backlog size is the number of messages that have accumulated on an asynchronous consumer, but which have not been passed to a message listener.

Configuring a Message Pipeline

You can control a client's maximum pipeline size by configuring the Messages Maximum per Session attribute on the client's connection factory, which is defined as the "maximum number of messages that can exist for an asynchronous consumer and that have not yet been passed to the message listener". The default setting is 10. For more information on configuring a JMS connection factory, see "Configure connection factories" in the Oracle WebLogic Server Administration Console Online Help.

Behavior of Pipelined Messages

Once a message pipeline is configured, it will exhibit the following behavior:

Statistics — JMS monitoring statistics reports backlogged messages in a message pipeline as pending (for queues and durable subscribers) until they are either committed or acknowledged.
Performance — Increasing the Messages Maximum pipeline size may improve performance for high-throughput applications. Note that a larger pipeline will increase client memory usage, as the pending pipelined messages accumulate on the client JVM before the asynchronous consumer's listener is called.
Sorting — Messages in an asynchronous consumer's pipeline are not sorted according to the consumer destination's configured sort order; instead, they remain in the order in which they are pushed from the JMS server. For example, if a destination is configured to sort by priority, high priority messages will not jump ahead of low priority messages that have already been pushed into an asynchronous consumer's pipeline.

Notes:
The Messages Maximum per Session pipeline size setting on the connection factory is not related to the Messages Maximum quota settings on JMS servers and destinations.
Pipelined messages are sometimes aggregated into a single message on the network transport. If the messages are sufficiently large, the aggregate size of the data written may exceed the maximum value for the transport, which may cause undesirable behavior. For example, the t3 protocol sets a default maximum message size of 10,000,000 bytes, and is configurable on the server with the MaxT3MessageSize attribute. This means that if ten 2 megabyte messages are pipelined, the t3 limit may be exceeded.

Receive Messages Synchronously using the Simplified API

The receive methods on a JMSConsumer object are used for synchronous delivery of messages.

public String receiveMessage(
ConnectionFactory connectionFactory,Queue queue){
   String body=null;
   try (JMSContext context = connectionFactory.createContext();){
      JMSConsumer consumer = session.createConsumer(queue);
      body = consumer.receiveBody(String.class);
   } catch (JMSRuntimeException ex) {
      // handle exception
   }
   return body;
}

For additional information about the JMSConsumer class methods, see the javax.jms.JMSConsumer Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/JMSConsumer.html.

Receiving Messages Synchronously using the Classic API

To receive messages synchronously, use the following MessageConsumer methods:

public Message receive(
) throws JMSException

public Message receive(
 long timeout
) throws JMSException

public Message receiveNoWait(
) throws JMSException

In each case, the application receives the next message produced. If you call the receive() method with no arguments, the call blocks indefinitely until a message is produced or the application is closed. Alternatively, you can pass a timeout value to specify how long to wait for a message. If you call the receive() method with a value of 0, the call blocks indefinitely. The receiveNoWait() method receives the next message if one is available, or returns null; in this case, the call does not block.

The MessageConsumer class methods are inherited by the QueueReceiver and TopicSubscriber classes. For additional information about the MessageConsumer class methods, see the javax.jms.MessageConsumer Javadoc, at http://docs.oracle.com/javaee/7/api/javax/jms/MessageConsumer.html.

Example: Receiving Messages Synchronously Within a PTP Application

The following example is excerpted from the examples.jms.queue.QueueReceive example, provided with WebLogic Server in the EXAMPLES_HOME\wl_server\examples\src\examples\jms\queue directory, where EXAMPLES_HOME represents the directory in which the WebLogic Server code examples are configured. Rather than set a message listener, you would call qreceiver.receive() for each message. For example:

qreceiver = qsession.createReceiver(queue);
qreceiver.receive();

The first line creates the queue receiver on the queue. The second line executes a receive() method. The receive() method blocks and waits for a message.

Example: Receiving Messages Synchronously Within a Pub/Sub Application

The following example is excerpted from the examples.jms.topic.TopicReceive example, provided with WebLogic Server in the EXAMPLES_HOME\wl_server\examples\src\examples\jms\topic directory, where EXAMPLES_HOME represents the directory in which the WebLogic Server code examples are configured. Rather than set a message listener, you would call tsubscriber.receive() for each message.

For example:

tsubscriber = tsession.createSubscriber(topic);
Message msg = tsubscriber.receive();
msg.acknowledge();

The first line creates the topic subscriber on the topic. The second line executes a receive() method. The receive() method blocks and waits for a message.

Use Prefetch Mode to Create a Synchronous Message Pipeline

In releases prior to WebLogic Server 9.1, synchronous consumers required making a two-way network calls for each message, which was an inefficient model because the synchronous consumer could not retrieve multiple messages, and could also increase network traffic resources, since synchronous consumers would continually poll the server for available messages. In WebLogic 9.1 or later, your synchronous consumers can also use the same efficient behavior as asynchronous consumers by enabling the Prefetch Mode for Synchronous Consumers option on JMS connection factories, either using the WebLogic Server Administration Console or the JMSClientParamsBean MBean.

Similar to the asynchronous message pipeline, when the Prefetch Mode is enabled on a JMS client's connection factory, the connection factory's targeted JMS servers will proactively push batches of unconsumed messages to synchronous message consumers, using the connection factory's Messages Maximum per Session parameter to define the maximum number of messages per batch. This may improve performance because messages are ready and waiting for synchronous consumers when the consumers are ready to process more messages, and it may also reduce network traffic by reducing synchronous calls from consumers that must otherwise continually poll for messages.

Synchronous message prefetching does not support user (XA) transactions for synchronous message receives or multiple synchronous consumers per session (regardless of queue or topic). In most such cases, WebLogic JMS will silently and safely ignore the Prefetch Mode for Synchronous Consumer flag; however, otherwise WebLogic will fail the application's synchronous receive calls.

For more information on the behavior of pipelined messages, see Asynchronous Message Pipeline. For more information on configuring a JMS connection factory, see "Configure connection factories" in the Oracle WebLogic Server Administration Console Online Help.

Recovering Received Messages

Note:

This section applies only to non-transacted sessions for which the acknowledge mode is set to CLIENT_ACKNOWLEDGE. Synchronously received AUTO_ACKNOWLEDGE messages may not be recovered; they have already been acknowledged.

An application can request that JMS redeliver messages (unacknowledge them) using the following method:

public void recover(
) throws JMSException

The recover() method performs the following steps:

Stops message delivery for the session
Tags all messages that have not been acknowledged (but may have been delivered) as redelivered
Resumes sending messages starting from the first unacknowledged message for that session

Note:
Messages in queues are not necessarily re-delivered in the same order that they were originally delivered, nor to the same queue consumers. For information to guarantee the correct ordering of re-delivered messages, see Ordered Redelivery of Messages.

Acknowledging Received Messages

Note:

This section applies only to non-transacted sessions for which the acknowledge mode is set to CLIENT_ACKNOWLEDGE.

To acknowledge a received message, use the following Message method:

public void acknowledge(
) throws JMSException

The acknowledge() method depends on how the connection factory's Acknowledge Policy attribute is configured, as follows:

The default policy of "All" specifies that calling acknowledge on a message acknowledges all unacknowledged messages received on the session.
The "Previous" policy specifies that calling acknowledge on a message acknowledges only unacknowledged messages up to, and including, the given message. Messages that are not acknowledged may be redelivered to the client.

This method is effective only when issued by a non-transacted session for which the acknowledge mode is set to CLIENT_ACKNOWLEDGE. Otherwise, the method is ignored.

Releasing Object Resources

When you have finished using the connection, session, message producer or consumer, connection consumer, or queue browser created on behalf of a JMS application, you should explicitly close them to release the resources.

Enter the close() method to close JMS objects, as follows:

public void close(
) throws JMSException

When closing an object:

The call blocks until the method call completes or until any outstanding asynchronous receiver onMessage() calls complete.
All associated sub-objects are also closed. For example, when closing a session, all associated message producers and consumers are also closed. When closing a connection, all associated sessions are also closed.

For more information about the impact of the close() method for each object, see the appropriate javax.jms Javadoc, at http://www.oracle.com/technetwork/java/jms/index.html. In addition, for more information about the connection or Session close() method, see Starting, Stopping, and Closing a Connection or Closing a Session, respectively.

The following example is excerpted from the examples.jms.queue.QueueSend example, provided with WebLogic Server in the EXAMPLES_HOME\wl_server\examples\src\examples\jms\queue directory, where EXAMPLES_HOME represents the directory in which the WebLogic Server code examples are configured. This example shows the code required to close the message consumer, session, and connection objects.

public void close(
) throws JMSException
{
 qreceiver.close();
 qsession.close();
 qcon.close();
}

In the QueueSend example, the close() method is called at the end of main() to close objects and free resources.