This book begins with the installation of Glassfish 3 and deploying Java applications. It also explains how to develop, configure, package, and deploy servlets. Additionally, we will learn the processing of HTML forms. As we move on, we will develop Java Server Pages and get to know about implicit JSP objects. We will also get to know about all the JSTL (JSP Standard Tag Library) tag libraries. This book gives us a better understanding on how to manage data from a database through the Java Database Connectivity (JDBC) API and the Java Persistence API (JPA). We will also learn more about the newly introduced features of JPA 2.0 and develop JSF 2.0 applications to learn how to customize them. We will then set up Glassfish for the Java Messaging (JMS) API and understand the working of message queues and message topics. Later, we will use the Context and Dependency Injection (CDI) API to integrate application layers and study the SOAP-based web service development using the JAX-WS specification. Finally, we will learn more about the RESTful web service development using the JAX-RS specification.
also read:
- Java EE Tutorials
- Java EE 7 Tutorials
- Java EE Interview Questions
The book covers the various Java EE 6 conventions and annotations that can simplify enterprise Java application development. The latest versions of the Servlet, JSF, JPA, EJB, and JAX-WS specifications are covered, as well as new additions to the specification, such as JAX-RS and CDI.
What This Book Covers
Chapter 1, Getting Started with GlassFish will discuss how to download and install GlassFish. We will look at several methods of deploying a Java EE application through the GlassFish web console, through the asadmin command, and by copying the file to the autodeploy directory. We will cover basic GlassFish administration tasks such as setting up domains and setting up database connectivity by adding connection pools and data sources.
Chapter 2, Servlet Development and Deployment will cover how to develop, configure, package, and deploy servlets. We will also cover how to process HTML form information by accessing the HTTP request object. Additionally, forwarding HTTP requests from one servlet to another will be explained, as well as redirecting the HTTP response to a different server. We will discuss how to persist objects in memory across requests by attaching them to the servlet context and the HTTP session. Finally, we will look at all the major new features of Servlet 3.0, including configuring web applications via annotations, pluggability through web-fragment. xml , programmatic servlet configuration, and asynchronous processing.
Chapter 3, JavaServer Pages will talk about how to develop and deploy simple JSPs. We will cover how to access implicit objects such as request, session, and so on, from JSPs. Additionally, we will look at how to set and get the values of JavaBean properties via the <jsp:useBean> tag. In addition to that, we will find out how to include a JSP into another JSP at runtime via the <jsp:include> tag, and at compilation time via the JSP include directive. We will discuss how to write custom JSP tags by extending javax.servlet.jsp.tagext.SimpleTagSupport or by writing TAG files. We will also discuss how to access JavaBeans and their properties via the Unified Expression Language. Finally, we will cover the JSP XML syntax that allows us to develop XMLcompliant
JavaServer Pages.
Chapter 4, JSP Standard Tag Library will cover all JSP Standard Tag Library tags, including the core, formatting, SQL, and XML tags. Additionally, JSTL functions will be explained. Examples illustrating the most common JSTL tags and functions will be provided; additional JSTL tags and functions will be mentioned and described.
Chapter 5, Database Connectivity will talk about how to access data in a database via both the Java Database Connectivity (JDBC) and through the Java Persistence API (JPA). Defining both unidirectional and bidirectional one-to-one, one-to-many, and many-to-many relationships between JPA entities will be covered. Additionally, we will discuss how to use JPA composite primary keys by developing custom primary key classes. We will also discuss how to retrieve entities from a database by using the Java Persistence Query Language (JPQL). We will look at how to build queries programmatically through the JPA 2.0 Criteria API and automating data validation through JPA 2.0’s Bean Validation support
Chapter 6,JavaServer Faces will cover how to develop web-based applications using JavaServer Faces—the standard component framework for the Java EE 5 platform. We will talk about how to write a simple application by creating JSPs containing JSF tags and managed beans. We will discuss how to validate user input by using JSF’s standard validators and by creating our own custom validators, or by writing validator methods. Additionally, we will look at how to customize standard JSF error messages; both the message text and the message style (font, color, and so on). Finally, we will discuss how to write applications by integrating JSF and the Java Persistence API (JPA).
Chapter 7, Java Messaging Service will talk about how to set up JMS connection factories, JMS message queues, and JMS message topics in GlashFish using the GlashFish web console. We will cover how to send and receive messages to and from a message queue. We will discuss how to send and receive messages to and from a JMS message topic. We will find out how to browse messages in a message queue without
removing the messages from the queue. Finally, we will look at how to set up and interact with durable subscriptions to JMS topics.
Chapter 8, Security will talk about how to use GlashFish’s default realms to authenticate our web applications. We will cover the file realm, which stores user information in a flat file, and the certificate realm, which requires client-side certificates for user authentication. Additionally, we will discuss how to create additional realms that behave just like the default realms, by using the realm classes included with GlashFish.
Chapter 9, Enterprise JavaBeans will cover how to implement business logic via stateless and stateful session beans. Additionally, we will explain the concept of containermanaged transactions and bean-managed transactions. We will look at the life cycles for the different types of Enterprise Java Beans. We will talk about how to have EJB methods invoked periodically by the EJB container, by taking advantage of the EJB timer service. Finally, we will explain how to make sure that EJB methods are only invoked by authorized users.
Chapter 10, Contexts and Dependency Injection will talk about how JSF pages can access CDI named beans as if they were JSF managed beans. We will explain how CDI makes it easy to inject dependencies into our code. We will discuss how we can use qualifiers to determine what specigic implementation of dependency to inject into our code. Finally, we will look at all the scopes that a CDI bean can be placed into.
Chapter 11, Web Services with JAX-WS will cover how to develop web services and web service clients via the JAX-WS API. We will discuss how to send attachments to a web service. We will explain how to expose an EJB’s methods as web services. Finally, we will look at how to secure web services so that they are not accessible to unauthorized clients.
Chapter 12, RESTful Web Services with Jersey and JAX-RS will discuss how to easily develop RESTful web services using JAX-RS—a new addition to the Java EE specification. We will explain how to automatically convert data between Java and XML by taking advantage of the Java API for XML Binding (JAXB). Finally, we will cover how to pass parameters to our RESTful web services via the @PathParam and
@QueryParam annotations.
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 chapter, we will cover the following topics:
- Setting up GlashFish for JMS
- Working with message queues
- Working with message topics
Setting up GlassFish for JMS
Before we start writing code to take advantage of the JMS API, we need to configure some GlashFish 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 GlashFish’s web console. Recall from Chapter 1 that 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 Name and 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 chapter 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 GlashFish 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 Resources node, 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 GlashFish is very similar to setting up a message queue. In the GlashFish 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 mess age 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 GlashFish 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 called jmsptpproducer.jar, we would type the following command in the command line:
appclient -client jmsptpproducer.jar
We would then see, after some GlashFish 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 [GlashFish installation directory]/GlashFish/bin. The previous example assumes this directory is in your PATH variable. If it isn’t the complete path to the appclient executable, 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 GlashFish 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.Session interface.
- 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 the createProducer() 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 the createProducer() 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 GlashFish 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:
For more information on all of these message types, consult their JavaDoc documentation at http://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 of javax.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.Message interface. 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 the
close() 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 the appclient 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.MessageConsumer obtained from the JMS session. We pass an instance of our custom implementation of javax.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 GlashFish’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.
Message topics
Message topics are used when our JMS code uses the publish/subscribe (pub/sub) messaging domain. When using this messaging domain, the same message can be sent to all subscribers of the topic.
Sending messages to a message topic
The following example illustrates how to send messages to a message topic:
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.Session;
import javax.jms.TextMessage;
import javax.jms.Topic;
public class MessageSender
{
@Resource(mappedName = "jms/GlassFishBookConnectionFactory")
private static ConnectionFactory connectionFactory;
@Resource(mappedName = "jms/GlassFishBookTopic")
private static Topic topic;
public void produceMessages()
{
MessageProducer messageProducer;
TextMessage textMessage;
try
{
Connection connection = connectionFactory.createConnection();
Session session = connection.createSession(false,
Session.AUTO_ACKNOWLEDGE);
messageProducer = session.createProducer(topic);
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();
}
}
As we can see, this code is nearly identical to the MessageSender class we saw when we discussed point-to-point messaging. As a matter of fact, the only lines of code that are different are the ones that are highlighted. The JMS API was designed this way so that application developers do not have to learn two different APIs for the PTP and pub/sub domains. As the code is nearly identical to the corresponding example in the Message queues section, we will only explain the differences between the two examples. In this example, instead of declaring an instance of a class implementing javax.jms. Queue, we declare an instance of a class implementing javax.jms.Topic. Just like in the previous examples, we use dependency injection to initialize the Topic object. After obtaining a JMS connection and a JMS session, we pass the Topic object to the createProducer() method in the Session object. This method returns an instance of javax.jms.MessageProducer that we can use to send messages to the JMS topic.
Receiving messages from a message topic
Just as sending messages to a message topic is nearly identical to sending messages to a message queue, receiving messages from a message topic is nearly identical to receiving messages from 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.MessageConsumer;
import javax.jms.Session;
import javax.jms.TextMessage;
import javax.jms.Topic;
public class MessageReceiver
{
@Resource(mappedName = "jms/GlassFishBookConnectionFactory")
private static ConnectionFactory connectionFactory;
@Resource(mappedName = "jms/GlassFishBookTopic")
private static Topic topic;
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(topic);
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();
}
}
Once again, the differences between this code and the corresponding code for PTP are trivial. Instead of declaring an instance of a class implementing javax.jms.Queue, we declare a class implementing javax.jms.Topic. We use the @Resource annotation to inject an instance of this class into our code using the JNDI name we used when creating it in the GlashFish web console. After obtaining a JMS connection and a JMS session, we pass the Topic object to the createConsumer() method in the Session object. This method returns an instance of javax.jms.MessageConsumer that we can use to receive messages from the JMS topic. Using the pub/sub messaging domain as illustrated in this section has the advantage that messages can be sent to several message consumers. This can be easily tested by concurrently executing two instances of the MessageReceiver class we developed in this section, then executing the MessageSender class we developed in the previous section. We should see console output for each instance, indicating that both instances received all messages. Just like with message queues, messages can be retrieved asynchronously from a message topic. The procedure to do this is so similar to the message queue version that we will not show an example. To convert the asynchronous example shown earlier in this chapter to use a message topic, simply replace the javax.jms.Queue variable with an instance of javax.jms.Topic and inject the appropriate instance by using "jms/GlassFishBookTopic" as the value of the mappedName attribute of the @Resource annotation decorating the instance of javax.jms.Topic.
Creating durable subscribers
The disadvantage of using the pub/sub messaging domain is that message consumers must be executing when messages are sent to the topic. If the message consumer is not executing at the time, it will not receive the messages, whereas in PTP, messages are kept in a queue until the message consumer executes. Fortunately, the JMS API provides a way to use the pub/sub messaging domain and keep messages in the topic until all subscribed message consumers execute and receive the message. This can be accomplished by creating durable subscribers to a JMS topic. In order to be able to service durable subscribers, we need to set the ClientId property of our JMS connection factory. Each durable subscriber must have a unique client id, therefore a unique connection factory must be declared for each potential durable subscriber.
InvalidClientIdException?
Only one JMS client can connect to a topic for a specific client id. If more
than one JMS client attempts to obtain a JMS connection using the same
connection factory, a JMSException stating that the client id is already in
use will be thrown. The solution is to create a connection factory for each
potential client that will be receiving messages from the durable topic.
Like we mentioned before, the easiest way to add a connection factory is through the GlashFish web console. Recall that to add a JMS connection factory through the GlashFish web console, we need to expand the Resources node on the left hand side, then expand the JMS Resources node, click on the Connection Factories node, and click on the New... button in the main area of the page. Our next example will use the settings displayed in the following screenshot:
Before clicking on the OK button, we need to scroll to the bottom of the page, click on the Add Property button, and enter a new property named ClientId. Our example will use ExampleId as the value for this property.
Now that we have set up GlashFish to be able to provide durable subscriptions, we are ready to write some code to take advantage of them:
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.Session;
import javax.jms.TextMessage;
import javax.jms.Topic;
public class MessageReceiver
{
@Resource(mappedName = "jms/GlassFishBookDurableConnectionFactory")
private static ConnectionFactory connectionFactory;
@Resource(mappedName = "jms/GlassFishBookTopic")
private static Topic topic;
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.createDurableSubscriber(topic,
"Subscriber1");
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();
}
}
As we can see, this code is not much different from the previous examples whose purpose was to retrieve messages. There are only two differences from the previous examples: the instance of ConnectionFactory to which we are injecting is the one we set up earlier in this section to handle durable subscriptions, and instead of calling the createSubscriber() method on the JMS session object, we are calling createDurableSubscriber() . The createDurableSubscriber() method takes two arguments: a JMS Topic object to retrieve messages from and a string designating a name for this subscription. This second parameter must be unique between all subscribers to the durable topic.
Summary
In this chapter, we covered how to set up JMS connection factories, JMS message queues, and JMS message topics in GlashFish using the GlashFish web console. We also covered how to send messages to a message queue via the javax.jms.MessageProducer interface.
Additionally, we covered how to receive messages from a message queue via the javax.jms.MessageConsumer interface. We also covered how to asynchronously receive messages from a message queue by implementing the javax.jms.MessageListener interface. We also saw how to use these interfaces to send and receive messages to and from a JMS message topic. We covered how to browse messages in a message queue without removing the messages from the queue via the javax.jms.QueueBrowser interface. Finally, we saw how to set up and interact with durable subscriptions to JMS topics.
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