Creating an Enterprise Application

Summary

In this exercise you created a Java EE 5 enterprise application containing an EJB module and a web module.

Creating a Persistence Unit

First you create a persistence unit that defines the data source and entity manager used in our application.

When you click Finish, the IDE creates persistence.xml and opens it in the Source Editor in Design view. Close persistence.xml.

Creating the NewsEntity Entity Class

In this exercise you will create the NewsEntity entity class. An entity class is a simple Java class that generally represents a table in a database. When you create the entity class, the IDE adds the @Entity annotation to define the class as an entity class. After you create the class, you will create fields in the class to represent the data that you want in your table.

Each entity class must have a primary key. When you create the entity class, the IDE adds the @Id annotation to declare which field to use as the primary key. The IDE also adds the @GeneratedValue annotation and specifies the key generation strategy for the primary Id.

To create the NewsEntity class, do the following:

When you click Finish, the entity class NewsEntity.java opens in the Source Editor. In the Source Editor, do the following:

private String title;
private String body;

In the next step you will create the NewMessage message-driven bean.

Creating the NewMessage Message-Driven Bean

Now you will create the NewMessage message-driven bean in your EJB module. You will use the New Message-Driven Bean wizard to create the bean and the necessary JMS resources.

To create the NewMessage message-driven bean, do the following:

When you click Finish, the new message-driven bean class NewMessageBean.java opens in the Source Editor. You can see that the @MessageDriven annotation and configuration properties are added to the class.

@MessageDriven(mappedName = "jms/NewMessage", activationConfig =  {
        @ActivationConfigProperty(propertyName = "acknowledgeMode", propertyValue = "Auto-acknowledge"),
        @ActivationConfigProperty(propertyName = "destinationType", propertyValue = "javax.jms.Queue")
    })

This annotation tells the container that the component is a message-driven bean and the JMS resource used by the bean. When the IDE generates the class, the Mapped Name of the resource (jms/NewMessage) is derived from the name of the class (NewMessage.java). The JMS resource is mapped to the JNDI name of the destination from which the bean receives messages. The New Message-Driven Bean wizard has already add the information for the JMS resources to sun-resources.xml. The EJB 3.0 API enables you to look up objects in the JNDI namespace from within the bean class so that you do not need to configure deployment descriptors to specify the JMS resources.

The EJB 3.0 specifications allow you to use annotations to introduce resources directly into a class. You will now use annotations to introduce the MessageDrivenContext resource into your class, and then inject the PersistenceContext resource which will be used by the EntityManager API to manage the persistent entity instances. We will add the annotations to the class in the Source Editor.

public class NewMessageBean implements MessageListener {

@Resource
private MessageDrivenContext mdc;

@PersistenceContext
private EntityManager em;

public void persist(Object object) {
    em.persist(object);
}

public void save(Object object) {
    em.persist(object);
}

public void onMessage(Message message) {
    ObjectMessage msg = null;
    try {
        if (message instanceof ObjectMessage) {
            msg = (ObjectMessage) message;
            NewsEntity e = (NewsEntity) msg.getObject();
            save(e);
        }
    } catch (JMSException e) {
        e.printStackTrace();
        mdc.setRollbackOnly();
    } catch (Throwable te) {
        te.printStackTrace();
    }

Creating the Session Bean

Next you will create a session facade for the NewsEntity entity class. To create the session facade, do the following:

When you click Finish, the session facade class NewsEntityFacade.java is created and opens in the Source Editor. The IDE also creates the local interface NewsEntityFacadeLocal.java.

EJB 3.0 technology simplifies the creation of session beans by reducing the amount of required code. You can see that the annotation @Stateless is used to declare the class as a stateless session bean component and that the class no longer needs a statement implementing javax.ejb.SessionBean. The code is also much cleaner because with EJB 3.0 technology the business methods no longer need to have code declaring they throw checked exceptions.

You can see that the PersistenceContext resource was injected directly into the session bean component when we created the session facade.

Summary

In this exercise, you coded an entity class and a message-driven bean in the EJB module. You then created a session facade for the entity class. You also created the JMS resources that will be used by the application.

Creating the ListNews Servlet

In this exercise you will create a simple servlet for displaying our data. You will use annotations to call the entity bean from the servlet.

When you click Finish, the class ListNews.java opens in the Source Editor. In the Source Editor, do the following:

out.println("<h1>Servlet ListNews at " + request.getContextPath () + "</h1>");

List news = newsEntityFacade.findAll();
for (Iterator it = news.iterator(); it.hasNext();) {
    NewsEntity elem = (NewsEntity) it.next();
    out.println(" <b>"+elem.getTitle()+" </b><br />");
    out.println(elem.getBody()+"<br /> ");
}
out.println("<a href='PostMessage'>Add new message</a>");

out.println("</body>");
                    

Creating the PostMessage Servlet

In this exercise you will create the PostMessage servlet that will be used to post messages. You will use annotations to inject the JMS resources you created directly into the servlet, specifying the variable name and the name to which it is mapped. You will then add the code to send the JMS message and the code for the HTML form for adding a message.

When you click Finish, the class PostMessage.java opens in the Source Editor. In the Source Editor, do the following:

public class PostMessage extends HttpServlet {
    @Resource(mappedName="jms/NewMessageFactory")
    private  ConnectionFactory connectionFactory;

    @Resource(mappedName="jms/NewMessage")
    private  Queue queue;

response.setContentType("text/html;charset=UTF-8");

// Add the following code to send the JMS message
String title=request.getParameter("title");
String body=request.getParameter("body");
if ((title!=null) && (body!=null)) {
    try {
        Connection connection = connectionFactory.createConnection();
        Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
        MessageProducer messageProducer = session.createProducer(queue);

        ObjectMessage message = session.createObjectMessage();
        // here we create NewsEntity, that will be sent in JMS message
        NewsEntity e = new NewsEntity();
        e.setTitle(title);
        e.setBody(body);

        message.setObject(e);
        messageProducer.send(message);
        messageProducer.close();
        connection.close();
        response.sendRedirect("ListNews");

    } catch (JMSException ex) {
        ex.printStackTrace();
    }
}

PrintWriter out = response.getWriter();
                    

out.println("Servlet PostMessage at " + request.getContextPath() + "</h1>");

// The following code adds the form to the web page
out.println("<form>");
out.println("Title: <input type='text' name='title'><br/>");
out.println("Message: <textarea name='body'></textarea><br/>");
out.println("<input type='submit'><br/>");
out.println("</form>");

out.println("</body>");
                

Problem with JMS Resources

When using the wizard to create JMS resources, you may see the following server error message in the output window:

[com.sun.enterprise.connectors.ConnectorRuntimeException:
                    JMS resource not created : jms/Queue]
                

This message could indicate that the JMS resource was not created or was not registered with the application server. You can use the Admin Console of the application server to check, create and edit JMS resources.

To open the Admin Console, do the following:

You need to make sure that the JMS connection factory resource in the PostMessage servlet is mapped to the correct JNDI name of the JMS connection factory resource registered with the Sun Java System Application Server.

The following resources should be registered with the Sun Java System Application Server: