| <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> |
| |
| <!-- |
| Copyright (c) 2009, 2010, 2011 Oracle and/or its affiliates. All rights reserved. |
| --> |
| |
| <html> |
| <head> |
| <title>Creating an Enterprise Application with EJB 3.1</title> |
| <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" > |
| <meta name="description" content="A tutorial on how to use NetBeans IDE to develop an enterprise application using EJB 3.1 technology."> |
| <link rel="stylesheet" href="../../../netbeans.css"> |
| <meta name="author" content="ken ganfield"> |
| </head> |
| <body> |
| <h1>Creating an Enterprise Application with EJB 3.1</h1> |
| |
| <p>This tutorial takes you through the basics of developing a Java EE 6 enterprise application and |
| demonstrates some of the EJB 3.1 technology features that were introduced as part of the Java EE 6 specification. |
| In this tutorial you will create an enterprise application that enables a user to post to and retrieve messages from a database.</p> |
| |
| <p>The application contains an EJB module and a web module. |
| The EJB module contains an entity class, a session facade for the entity class |
| and a message-driven bean. The web module contains servlets for displaying and posting messages |
| and a singleton session bean that counts the number of users in the session.</p> |
| |
| <p>Before starting this tutorial you may want to familiarize yourself with |
| the following document.</p> |
| <ul> |
| <li><a href="javaee-gettingstarted.html">Getting Started with Java EE Applications</a></li> |
| </ul> |
| |
| |
| <p><b>Tutorial Exercises</b></p> |
| <img src="../../../images_www/articles/73/netbeans-stamp-80-74-73.png" class="stamp" alt="Content on this page applies to NetBeans IDE 7.2, 7.3, 7.4 and 8.0" title="Content on this page applies to the NetBeans IDE 7.2, 7.3, 7.4 and 8.0" > |
| <ul> |
| <li><a href="#intro">About the NewsApp Enterprise Application</a></li> |
| <li><a href="#Exercise_1">Creating the Enterprise Application Project</a></li> |
| <li><a href="#Exercise_2">Coding the EJB Module</a> |
| <ul> |
| <li><a href="#Exercise_2a">Creating the Entity Class</a></li> |
| <li><a href="#Exercise_2b">Creating the Message-Driven Bean</a></li> |
| <li><a href="#Exercise_2c">Creating the Session Facade</a></li> |
| </ul> |
| </li> |
| <li><a href="#Exercise_3">Coding the Web Module</a> |
| <ul> |
| <li><a href="#Exercise_3a">Creating the Singleton Session Bean</a></li> |
| <li><a href="#Exercise_3b">Creating the ListNews Servlet</a></li> |
| <li><a href="#Exercise_3c">Creating the PostMessage Servlet</a></li> |
| </ul> |
| </li> |
| <li><a href="#Exercise_4">Running the Project</a></li> |
| <li><a href="#Exercise_5">Downloading the Solution Project</a></li> |
| <li><a href="#Exercise_6">Troubleshooting</a></li> |
| </ul> |
| <p><b>To follow this tutorial, you need the following software and resources.</b></p> |
| <table> |
| <tbody> |
| <tr> |
| <th class="tblheader" scope="col">Software or Resource</th> |
| <th class="tblheader" scope="col">Version Required</th> |
| </tr> |
| <tr> |
| <td class="tbltd1"><a href="https://netbeans.org/downloads/index.html">NetBeans IDE</a></td> |
| <td class="tbltd1">7.2, 7.3, 7.4, 8.0, Java EE version</td> |
| </tr> |
| <tr> |
| <td class="tbltd1"><a href="http://www.oracle.com/technetwork/java/javase/downloads/index.html">Java Development Kit (JDK)</a></td> |
| <td class="tbltd1">version 7 or 8</td> |
| </tr> |
| <tr> |
| <td class="tbltd1">GlassFish Server Open Source Edition</td> |
| <td class="tbltd1">3.x, 4.x</td> |
| </tr> |
| </tbody> |
| </table> |
| |
| <p><b>Prerequisites</b></p> |
| <p>This document assumes you have some basic knowledge of, or programming experience with, the following technologies:</p> |
| <ul> |
| <li>Java Programming</li> |
| <li>NetBeans IDE</li> |
| </ul> |
| <p class="tips">You can download <a href="https://netbeans.org/projects/samples/downloads/download/Samples/JavaEE/NewsAppEE6.zip">a zip archive of the finished project</a>.</p> |
| |
| <!-- ===================================================================================== --> |
| <a name="intro"></a> |
| <!--Exercise 1: --> |
| <h2>About the NewsApp Enterprise Application</h2> |
| <p>In this tutorial you will create a simple example of a multi-tiered, Java EE 6 enterprise application named NewsApp. |
| The NewsApp application uses some of the features introduced in the Java EE 6 specification.</p> |
| |
| <p>The structure of the NewsApp application generally corresponds to the following tiers.</p> |
| |
| <ul> |
| <li><strong>Web Tier.</strong> The Web Tier contains the presentation logic of the application and runs on a Java EE server. |
| In the NewsApp application, the Web Tier is represented by the web module and |
| contains servlets that access the business logic in the EJB module.</li> |
| <li><strong>Business Tier.</strong> Business Tier applications also run on Java EE servers and contain |
| the business logic of the application. |
| In the NewsApp application, the Business Tier is represented by the EJB module. |
| The EJB module contains the code that handles requests from the Web Tier clients and |
| manages transactions and how objects are persisted to the database.</li> |
| <li><strong>EIS Tier.</strong> The EIS Tier is the persistent storage layer of the application. |
| In the NewsApp application, this tier is represented by the database where the messages are stored.</li> |
| </ul> |
| |
| <p>When you build an enterprise application in the IDE, the EJB and web application modules are packaged in an EAR archive |
| that is then deployed to the server. The application is then typically accessed from the <strong>Client Tier.</strong> |
| The Client Tier is the environment where the client is run and is often a web browser on a user's local system.</p> |
| |
| <p class="notes"><strong>Note.</strong> In the example in this tutorial you will use a |
| single machine to host the Java EE server, the database and view the web pages. |
| In large enterprise applications, the different tiers are often distributed across multiple machines. |
| The Web Tier and Business Tier applications are often deployed to Java EE servers that are hosted on different machines.</p> |
| |
| |
| <p class="tips">For more details about the structure of Java EE enterprise applications, |
| see the chapter on <a href="http://download.oracle.com/javaee/6/tutorial/doc/bnaay.html">Distributed Multitiered Applications</a> |
| in the <a href="http://download.oracle.com/javaee/6/tutorial/doc/">Java EE 6 Tutorial, Part I</a>.</p> |
| |
| |
| <a name="Exercise_1"></a> |
| <!--Exercise 1: --> |
| <h2>Creating the Enterprise Application Project</h2> |
| <p>The goal of this exercise is to create the NewsApp enterprise application project. |
| You will use the New Project wizard to create an enterprise application that contains an EJB module and a web module.</p> |
| |
| |
| <ol> |
| <li>Choose File > New Project (Ctrl-Shift-N; ⌘-Shift-N on Mac) from the main menu.</li> |
| <li>Select Enterprise Application from the Java EE category and click Next. </li> |
| <li>Name the project <b>NewsApp</b> and set the project location.</li> |
| <li>Deselect the Use Dedicated Folder option, if selected.<br /> |
| (For this tutorial there is little reason to copy project libraries to a dedicated folder because |
| you will not need to share libraries with other users or projects.)<br /> |
| Click Next.</li> |
| <li>Set the server to GlassFish Server and set the Java EE Version to Java EE 6 or Java EE 7.</li> |
| <li>Select Create EJB Module and Create Web Application Module. Click Finish.</li> |
| </ol> |
| |
| <img src="../../../images_www/articles/72/javaee/ejbentapp/new-entapp-wizard.png" alt="New Project wizard" title="New Project wizard" class="margin-around b-all" /> |
| |
| <p>When you click Finish, the IDE creates three projects: NewsApp, NewsApp-ejb and NewsApp-war. |
| If you expand the NewsApp node in the Projects window, you can see that the enterprise application project does not contain any sources. |
| All the sources will be contained in the two modules that the wizard created and which are listed under the Java EE Modules node.</p> |
| <p>The enterprise application project only contains configuration and packaging details about the application. |
| When you build and run an enterprise application the IDE creates an EAR archive and deploys the EAR to the server. |
| In some cases, the enterprise application project will contain deployment descriptor files with additional information, but |
| deployment descriptor files are not required when you create a Java EE enterprise application that is deployed to GlassFish Server. |
| </p> |
| <img src="../../../images_www/articles/72/javaee/ejbentapp/ejb-projectswindow.png" alt="Projects window showing structure of the application" title="Projects window showing structure of the application" class="margin-around b-all" /> |
| |
| <a name="Exercise_2"></a> |
| <h2>Coding the EJB Module</h2> |
| <p>In this exercise you will create an entity class, a message-driven bean and a session facade in the EJB module. |
| You also will also create a persistence unit to provide the container with information about the data source and |
| how the entities are managed, and Java Message Service (JMS) resources that are used by the message-driven bean.</p> |
| |
| |
| <div class="indent"> |
| |
| <a name="Exercise_2a"></a> |
| <h3>Creating the Entity Class</h3> |
| <p>In this exercise you will create the <tt>NewsEntity</tt> 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 <tt>@Entity</tt> 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.</p> |
| <p>Each entity class must have a primary key. |
| When you create the entity class, the IDE adds the <tt>@Id</tt> annotation to declare which field to use as the primary key. |
| The IDE also adds the <tt>@GeneratedValue</tt> annotation and specifies the key generation strategy for the primary Id.</p> |
| <p>To create the <tt>NewsEntity</tt> class, perform the following steps.</p> |
| <ol> |
| <li>Right-click the EJB module in the Projects window and choose New > Other to open the New File wizard.</li> |
| <li>From the Persistence category, select Entity Class and click Next.</li> |
| <li>Type <strong>NewsEntity</strong> for the Class Name.</li> |
| <li>Type <strong>ejb</strong> for the Package.</li> |
| <li>Leave the Primary Key Type as <tt>Long</tt> in the New Entity Class wizard.</li> |
| <li>Select Create Persistence Unit. Click Next.</li> |
| <li>Keep the default Persistence Unit Name.</li> |
| <li>For the Persistence Provider, choose <tt>EclipseLink (JPA2.0)(default)</tt>.</li> |
| <li>For the Data Source, choose a data source (for example, select <tt>jdbc/sample</tt> if you want to use JavaDB).</li> |
| <li>Confirm that the persistence unit is using the Java Transaction API |
| and that the Table Generation Strategy is set to Create |
| so that the tables based on your entity classes are created when the application is deployed.<br/> |
| <img src="../../../images_www/articles/72/javaee/ejbentapp/new-pu-wizard.png" alt="screenshot of Provider and Database panel" title="Provider and Database panel" class="margin-around b-all" /> |
| </li> |
| <li>Click Finish.</li> |
| </ol> |
| <p>When you click Finish, the IDE creates <tt>persistence.xml</tt> and the entity class <tt>NewsEntity.java</tt>. |
| The IDE opens <tt>NewsEntity.java</tt> in the Source Editor.</p> |
| |
| <p>In the Source Editor, perform the following steps.</p> |
| |
| <ol> |
| <li>Add the following field declarations to the class: |
| <pre class="examplecode"> |
| private String title; |
| private String body;</pre> |
| </li> |
| <li>Right-click in the Source Editor and choose Insert Code (Alt-Insert; Ctrl-I on Mac) and |
| select Getter and Setter to open the Generate Getters and Setters dialog box.</li> |
| <li>Select the <tt>body</tt> and <tt>title</tt> fields in the dialog box. Click Generate.<br/> |
| <img src="../../../images_www/articles/72/javaee/ejbentapp/ejb-gettersetter.png" alt="Generate Getters and Setters dialog box" title="Generate Getters and Setters dialog box" class="margin-around b-all" /> |
| <p>When you click Generate, the IDE adds getter and setter methods for the fields.</p> |
| </li> |
| <li>Save the changes to <tt>NewsEntity.java</tt>.</li> |
| </ol> |
| <p>You can close <tt>NewsEntity.java</tt>.</p> |
| |
| <p class="tips">For more details about entity classes, |
| see the chapter <a href="http://java.sun.com/javaee/6/docs/tutorial/doc/bnbpz.html">Introduction to the Java Persistence API</a> |
| in the <a href="http://download.oracle.com/javaee/6/tutorial/doc/">Java EE 6 Tutorial, Part I</a>.</p> |
| |
| |
| |
| <a name="Exercise_2b"></a> |
| <h3>Creating the Message-Driven Bean</h3> |
| <p>In this exercise you will use a wizard to create the NewMessage message-driven bean in the EJB module. |
| The wizard will also help you to create the necessary JMS resources. |
| The message-driven bean receives and processes messages sent to the queue by a servlet |
| in the web module.</p> |
| |
| <p>To create the message-driven bean, perform the following steps:</p> |
| <ol> |
| <li>Right-click the EJB module in the Projects window and choose New > Other to open the New File wizard.</li> |
| <li>From the Enterprise JavaBeans category, select the Message-Driven Bean file type. Click Next.</li> |
| <li>Type <strong>NewMessage</strong> for the EJB Name.</li> |
| <li>Select <tt>ejb</tt> from the Package drop-down list.</li> |
| <li>Click the Add button next to the Project Destination field to open the Add Message Destination dialog box.</li> |
| <li>In the Add Message Destination dialog box, type <b>jms/NewMessage</b> and |
| select Queue for the destination type. Click OK.</li> |
| <li>Confirm that the project destination is correct. Click Finish.</li> |
| </ol> |
| <img src="../../../images_www/articles/72/javaee/ejbentapp/ejb-newmessage.png" alt="New Message-Driven Bean Wizard" title="New Message-Driven Bean Wizard" class="margin-around b-all" /> |
| <p>When you click Finish, the bean class <tt>NewMessage.java</tt> opens in the Source Editor. |
| You can see that the IDE added the <tt>@MessageDriven</tt> annotation and configuration properties to the class.</p> |
| <pre class="examplecode"> |
| @MessageDriven(mappedName = "jms/NewMessage", activationConfig = { |
| @ActivationConfigProperty(propertyName = "acknowledgeMode", propertyValue = "Auto-acknowledge"), |
| @ActivationConfigProperty(propertyName = "destinationType", propertyValue = "javax.jms.Queue") |
| }) |
| public class NewMessage implements MessageListener {</pre> |
| <p>The <tt>@MessageDriven</tt> annotation tells the container that the component is a message-driven bean and specifies the JMS resource used by the bean. |
| When the IDE generates the class, the Mapped Name of the resource (<tt>jms/NewMessage</tt>) is derived from the name of the class (<tt>NewMessage.java</tt>). |
| The JMS resource is mapped to the JNDI name of the destination from which the bean receives messages. |
| The New Message-Driven Bean wizard also adds the information for the JMS resources to <tt>glassfish-resources.xml</tt>. |
| You do not need to configure deployment descriptors to specify the JMS resources. |
| If you use the Run action in the IDE to deploy the application to GlassFish, the JMS resources are created on the server on deployment.</p> |
| |
| <p>The EJB specifications allow you to use annotations to introduce resources directly into a class. |
| You will now use annotations to introduce the <tt>MessageDrivenContext</tt> resource into your class, and then inject |
| the <tt>PersistenceContext</tt> resource which will be used by the EntityManager API to manage the persistent entity instances. |
| You will add the annotations to the class in the Source Editor.</p> |
| <ol> |
| <li>Inject the <tt>MessageDrivenContext</tt> resource into the class by adding the following |
| annotated field (in bold) to the class: |
| <pre class="examplecode"> |
| public class NewMessage implements MessageListener { |
| |
| <b>@Resource |
| private MessageDrivenContext mdc;</b></pre> |
| </li> |
| <li>Introduce the entity manager into the class by right-clicking in the code and choosing Insert Code (Alt-Insert; Ctrl-I on Mac) and |
| choosing Use Entity Manager from the pop-up menu. |
| The IDE adds the following <tt>@PersistenceContext</tt> annotation to your source code. |
| <pre class="examplecode"> |
| @PersistenceContext(unitName = "NewsApp-ejbPU") |
| private EntityManager em;</pre> |
| The IDE also generates the following <tt>persist</tt> method. |
| <pre class="examplecode"> |
| public void persist(Object object) { |
| em.persist(object); |
| }</pre> |
| </li> |
| <li>Modify the <tt>persist</tt> method to change the name to <tt>save</tt>. |
| The method should look like the following: |
| <pre class="examplecode"> |
| public void <b>save</b>(Object object) { |
| em.persist(object); |
| }</pre> |
| </li> |
| <li>Modify the <tt>onMessage</tt> method by adding the following code (in bold) to the body of the method. |
| <pre class="examplecode">public void onMessage(Message message) { |
| <strong>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(); |
| }</strong> |
| }</pre> |
| </li> |
| <li>Right-click in the editor and choose Fix Imports (Alt-Shift-I; ⌘-Shift-I on Mac) to generate any necessary import statements. Save your changes.</li> |
| </ol> |
| <p class="notes"><strong>Note.</strong> When generating the import statements, you want to <strong>make sure to import the <tt>javax.jms</tt> and <tt>javax.annotation.Resource</tt> libraries</strong>.</p> |
| |
| <p class="tips">For more details about message-driven beans, |
| see the chapter <a href="http://java.sun.com/javaee/6/docs/tutorial/doc/gipko.html">What is a Message-Driven Bean?</a> |
| in the <a href="http://download.oracle.com/javaee/6/tutorial/doc/">Java EE 6 Tutorial, Part I</a>.</p> |
| |
| <a name="Exercise_2c"></a> |
| <h3>Creating the Session Facade</h3> |
| <p>In this exercise you will create a session facade for the NewsEntity entity class. |
| The EJB 3.0 specification simplified the creation of session beans by reducing the amount of required code |
| and allowing the use of annotations to declare a class as a session bean. |
| The EJB 3.1 specification further simplifies the requirements for session beans by making business interfaces optional. |
| Sessions beans can be accessed by local clients either by a local interface or a no-interface view. |
| In this tutorial you will not create an interface for the bean. |
| The servlets in the web application will access the bean through a no-interface view.</p> |
| |
| <p>To create the session facade, perform the following steps:</p> |
| <ol> |
| <li>Right-click the EJB module and choose New > Other.</li> |
| <li>From the Persistence category, select Session Beans for Entity Classes. Click Next.</li> |
| <li>Select <tt>ejb.NewsEntity</tt> from the list of available entity classes and click Add to move the class to the Selected Entity |
| Classes pane. Click Next.</li> |
| <li>Check that the Package is set to <tt>ejb</tt>. Click Finish.</li> |
| </ol> |
| <img src="../../../images_www/articles/72/javaee/ejbentapp/ejb-sessionforentity.png" alt="New Message-Driven Bean Wizard" title="New Message-Driven Bean Wizard" class="margin-around b-all" /> |
| |
| |
| <p>When you click Finish, the IDE generates the session facade class <tt>NewsEntityFacade.java</tt> and |
| <tt>AbstractFacade.java</tt> and opens the files in the editor. |
| As you can see in the generated code, the annotation <tt>@Stateless</tt> is used to |
| declare <tt>NewsEntityFacade.java</tt> as a stateless session bean component. |
| The IDE also adds the <tt>PersistenceContext</tt> annotation to inject the resource directly into the session bean component. |
| <tt>NewsEntityFacade.java</tt> extends <tt>AbstractFacade.java</tt>, which |
| contains the business logic and manages the transaction.</p> |
| |
| <p class="notes"><strong>Note.</strong> Remote interfaces are still required if the beans will |
| be accessed by remote clients.</p> |
| |
| <p class="tips">For more information about session beans, |
| see the chapter <a href="http://java.sun.com/javaee/6/docs/tutorial/doc/gipjg.html">What is a Session Bean?</a> |
| in the <a href="http://download.oracle.com/javaee/6/tutorial/doc/">Java EE 6 Tutorial, Part I</a>.</p> |
| |
| </div> |
| |
| |
| |
| <!-- ===================================================================================== --> |
| <a name="Exercise_3"></a> |
| <h2>Coding the Web Module</h2> |
| <p>In this section you will create two servlets in the web module. |
| The ListNews servlet retrieves messages from the database through the entity facade in the EJB module. |
| The PostMessage servlet is used to send JMS messages.</p> |
| |
| <p>In this section you will also create a singleton session bean in the web module that will count the number of |
| users that are currently in the session. |
| The EJB 3.1 specification enables you to create enterprise beans in web applications. |
| Prior to EJB 3.1, all enterprise beans had to be in EJB modules.</p> |
| |
| <div class="indent"> |
| <a name="Exercise_3a"></a> |
| <h3>Creating the Singleton Session Bean</h3> |
| |
| <p>The EJB 3.1 specification introduces <tt>@Singleton</tt> annotation that enables you to easily create singleton session beans. |
| EJB 3.1 also defines additional annotations for configuring properties of singleton session beans such as when the bean is instantiated. |
| </p> |
| <p>After the singleton session bean is instantiated it exists for the lifecycle of the application. |
| As its name implies, there can only be a single instance of a singleton session bean in the application. |
| Like stateless session beans, singleton session beans can have multiple clients.</p> |
| |
| <p>To create the singleton session bean, perform the following steps. </p> |
| |
| <ol> |
| <li>Right-click the Web module and choose New > Other to open the New File wizard.</li> |
| <li>Select Session Bean in the Enterprise JavaBeans category. Click Next.</li> |
| <li>Type <strong>SessionManagerBean</strong> for the EJB Name.</li> |
| <li>Type <strong>ejb</strong> for the Package name.</li> |
| <li>Select Singleton. Click Finish.</li> |
| </ol> |
| <img src="../../../images_www/articles/72/javaee/ejbentapp/ejb-newsingleton.png" alt="Creating a singleton session bean in the New Session Bean wizard" title="Creating a singleton session bean in the New Session Bean wizard" class="margin-around b-all" /> |
| <p>When you click Finish, the IDE creates the singleton session bean class and opens the class in the editor. |
| You can see that the IDE added the annotation <tt>@Singleton</tt> to the class to declare a singleton session bean. |
| The wizard also annotated the class with <tt>@LocalBean</tt>.</p> |
| |
| <pre class="examplecode">@Singleton |
| @LocalBean |
| public class SessionManagerBean { |
| |
| }</pre> |
| |
| <ol> |
| <li>Annotate the class with <tt>@WebListener</tt> and implement <tt>HttpSessionListener</tt>. |
| <pre class="examplecode">@Singleton |
| @LocalBean |
| <strong>@WebListener</strong> |
| public class SessionManagerBean <strong>implements HttpSessionListener</strong>{ |
| |
| }</pre> |
| <p>The <tt>@WebListener</tt> annotation is part of the Servlet 3.0 API and enables you to |
| implement a listener directly in your code.</p> |
| |
| <p>When you implement <tt>HttpSessionListener</tt>, the IDE displays a warning |
| in the margin.</p> |
| </li> |
| <li>Click the warning badge in the left margin and choose "Implement all abstract methods".<br/> |
| <img src="../../../images_www/articles/72/javaee/ejbentapp/ejb-implementabstract.png" alt="Editor hint to implement abstract methods" title="Editor hint to implement abstract methods" class="margin-around b-all" /> |
| <p>The IDE adds the <tt>sessionCreated</tt> and <tt>sessionDestroyed</tt> methods.</p></li> |
| <li>Add the static field <tt>counter</tt> and set the initial value to <tt>0</tt>. |
| <pre class="examplecode">@LocalBean |
| @WebListener |
| public class SessionManagerBean implements HttpSessionListener{ |
| <strong>private static int counter = 0;</strong></pre> |
| </li> |
| <li>Modify the generated bodies of the <tt>sessionCreated</tt> and <tt>sessionDestroyed</tt> methods to increase |
| the value of a field when a new session starts and to decrease the value when a session finishes. |
| The value will be stored in the field <tt>counter</tt>. |
| |
| <pre class="examplecode">public void sessionCreated(HttpSessionEvent se) { |
| <strong>counter++;</strong> |
| } |
| |
| public void sessionDestroyed(HttpSessionEvent se) { |
| <strong>counter--;</strong> |
| }</pre> |
| |
| </li> |
| <li>Add the following method that returns the current value of <tt>counter</tt>. |
| <pre class="examplecode">public int getActiveSessionsCount() { |
| return counter; |
| }</pre> |
| <p>You will call this method from a servlet to display the current number of users/open sessions.</p> |
| </li> |
| <li>Save your changes.</li> |
| </ol> |
| |
| |
| <p>The code for the session bean should now look like the following.</p> |
| <pre class="examplecode">@Singleton |
| @LocalBean |
| @WebListener |
| public class SessionManagerBean implements HttpSessionListener { |
| private static int counter = 0; |
| |
| public void sessionCreated(HttpSessionEvent se) { |
| counter++; |
| } |
| |
| public void sessionDestroyed(HttpSessionEvent se) { |
| counter--; |
| } |
| |
| public int getActiveSessionsCount() { |
| return counter; |
| } |
| |
| }</pre> |
| <p class="tips">For more details about singleton session beans, |
| see the chapter <a href="http://java.sun.com/javaee/6/docs/tutorial/doc/gipjg.html">What is a Session Bean?</a> |
| in the <a href="http://download.oracle.com/javaee/6/tutorial/doc/">Java EE 6 Tutorial, Part I</a>.</p> |
| |
| |
| |
| |
| <a name="Exercise_3b"></a> |
| <h3>Creating the <tt>ListNews</tt> Servlet</h3> |
| <p>In this exercise you will create a simple servlet for displaying the stored messages. |
| You will use annotations to call the enterprise bean NewsEntityFacade from the servlet.</p> |
| <ol> |
| <li>Right-click the web module project and choose New > Servlet.</li> |
| <li>Type <strong>ListNews</strong> for the Class Name.</li> |
| <li>Enter <strong>web</strong> for the Package name. Click Finish.</li> |
| </ol> |
| <p>When you click Finish, the class <tt>ListNews.java</tt> opens in the Source Editor. |
| In the source editor, perform the following steps.</p> |
| <ol> |
| <li>Right-click in the source editor and choose Insert Code (Alt-Insert; Ctrl-I on Mac) and select Call Enterprise Bean.</li> |
| <li>In the Call Enterprise Bean dialog box, expand the NewsApp-ejb node and select NewsEntityFacade. Click OK. |
| <p>The IDE adds the <tt>@EJB</tt> annotation to inject the enterprise bean.</p> |
| </li> |
| <li>Use the Call Enterprise Bean dialog box again to inject the SessionManagerBean under the NewsApp-war node. |
| <p>In your code you will see the following annotations that inject the two enterprise beans.</p> |
| <pre class="examplecode">@WebServlet(name = "ListNews", urlPatterns = {"/ListNews"}) |
| public class ListNews extends HttpServlet { |
| |
| @EJB |
| private SessionManagerBean sessionManagerBean; |
| @EJB |
| private NewsEntityFacade newsEntityFacade; |
| </pre> |
| <p>You can also see that the <tt>@WebServlet</tt> annotation is used to declare the class a servlet |
| and to specify the servlet name. The <tt>@WebServlet</tt> annotation is part of the Servlet 3.0 API introduced |
| in the Java EE 6 specification. You can identify servlets using the annotation instead of in |
| the <tt>web.xml</tt> deployment descriptor. The NewsApp application does not contain <tt>web.xml</tt>.</p> |
| </li> |
| |
| <li>In the <tt>processRequest</tt> method, add the following code (in bold) to return the current session or create a new one. |
| <pre class="examplecode">protected void processRequest(HttpServletRequest request, HttpServletResponse response) |
| throws ServletException, IOException { |
| <strong>request.getSession(true);</strong> |
| response.setContentType("text/html;charset=UTF-8");</pre> |
| |
| <li>Add the following code (in bold) to the <tt>processRequest</tt> method |
| to print the messages and add a link to the PostMessage servlet. (Uncomment the code in the method if necessary.) |
| <pre class="examplecode"> |
| out.println("<h1>Servlet ListNews at " + request.getContextPath () + "</h1>"); |
| |
| <strong>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>");</strong> |
| |
| out.println("</body>"); |
| </pre> |
| </li> |
| <li>Add the following code (in bold) to retrieve and print the number of users/open sessions. |
| <pre class="examplecode">out.println("<a href='PostMessage'>Add new message</a>"); |
| |
| <strong>out.println("<br><br>"); |
| out.println(sessionManagerBean.getActiveSessionsCount() + " user(s) reading the news.");</strong> |
| |
| out.println("</body>"); |
| </pre> |
| </li> |
| <li>Press Ctrl-Shift-I to generate any necessary import statements for the class. |
| When generating the import statements, you want to <b>import the <tt>java.util</tt> libraries</b>.</li> |
| <li>Save the changes to the file.</li> |
| </ol> |
| |
| |
| <a name="Exercise_3c"></a> |
| <h3>Creating the <tt>PostMessage</tt> Servlet</h3> |
| <p>In this exercise you will create the <tt>PostMessage</tt> 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.</p> |
| <ol> |
| <li>Right-click the web module project and choose New > Servlet.</li> |
| <li>Type <tt>PostMessage</tt> for the Class Name.</li> |
| <li>Enter <tt>web</tt> for the Package name and click Finish.</li> |
| </ol> |
| <p>When you click Finish, the class <tt>PostMessage.java</tt> opens in the source editor. |
| In the source editor, perform the following steps.</p> |
| <ol> |
| <li>Use annotations to inject the <tt>ConnectionFactory</tt> and <tt>Queue</tt> resources by adding the following field declarations (in bold): |
| <pre class="examplecode">@WebServlet(name="PostMessage", urlPatterns={"/PostMessage"}) |
| public class PostMessage extends HttpServlet { |
| <b>@Resource(mappedName="jms/NewMessageFactory") |
| private ConnectionFactory connectionFactory; |
| |
| @Resource(mappedName="jms/NewMessage") |
| private Queue queue;</b></pre> |
| </li> |
| <li>You now add the code to send the JMS messages by adding the following code in bold to the <tt>processRequest</tt> method: |
| <pre class="examplecode"> |
| response.setContentType("text/html;charset=UTF-8"); |
| |
| // Add the following code to send the JMS message |
| <b>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(); |
| } |
| }</b> |
| |
| PrintWriter out = response.getWriter(); |
| </pre> |
| </li> |
| <li>Add the following lines (in bold) to the <tt>processRequest</tt> method to add the web form for adding a message. |
| (Uncomment the code to print the HTML if necessary.) |
| <pre class="examplecode"> |
| out.println("Servlet PostMessage at " + request.getContextPath() + "</h1>"); |
| |
| // The following code adds the form to the web page |
| <b>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>");</b> |
| |
| out.println("</body>"); |
| </pre> |
| <li>Press Ctrl-Shift-I to generate any necessary import statements for the class. |
| <p class="notes"><b>Note:</b> When selecting the libraries to import for <tt>Connection</tt>, <tt>ConnectionFactory</tt>, <tt>Session</tt> and |
| <tt>Queue</tt>, <b>confirm that you import the <tt>javax.jms</tt> libraries</b>. </p> |
| <img src="../../../images_www/articles/72/javaee/ejbentapp/import-jms.png" alt="screenshot of Fix All Imports dialog" title="Select the JMS libraries in the Fix All Imports dialog" class="margin-around b-all" /> |
| </li> |
| <li>Save your changes to the file.</li> |
| </ol> |
| </div> |
| |
| |
| <h2><a name="Exercise_4"></a> Running the Project</h2> |
| <p>You can now run the project. |
| When you run the project, you want the browser to open to the page with the <tt>ListNews</tt> servlet. |
| You do this by specifying the URL in the Properties dialog box for the enterprise application. |
| The URL is relative to the context path for the application. |
| After you enter the relative URL, you can build, deploy and run the application from the Projects window.</p> |
| <p>To set the relative URL and run the application, do the following:</p> |
| <ol> |
| <li>In the Projects window, right-click the NewsApp enterprise application node and select Properties in the pop-up menu.</li> |
| <li>Select Run in the Categories pane.</li> |
| <li>In the Relative URL textfield, type <strong>/ListNews</strong>.</li> |
| <li>Click OK.</li> |
| <li>In the Projects window, right-click the NewsApp enterprise application node and choose Run.</li> |
| </ol> |
| |
| <p>When you run the project, the <tt>ListNews</tt> servlet opens in your browser and displays a list of the messages in the database. |
| When you first run the project, the database is empty, but you can click Add Message to add a message.</p> |
| <img src="../../../images_www/articles/72/javaee/ejbentapp/ejb-browser1.png" alt="The ListNews Servlet page" title="The ListNews Servlet page" class="margin-around b-all" /> |
| <p>When you add a message with the <tt>PostMessage</tt> servlet, the message is sent to the |
| message-driven bean for writing to persistent storage, and the <tt>ListNews</tt> servlet is called to display the messages in the database. |
| The list of messages in the database retrieved by <tt>ListNews</tt> often does not yet contain the new message because our message service is asynchronous. |
| </p> |
| |
| <a name="Exercise_5"></a> |
| <h2>Downloading the Solution Project</h2> |
| <p>You can download the solution to this tutorial as a project in the following ways.</p> |
| <ul> |
| <li>Download <a href="https://netbeans.org/projects/samples/downloads/download/Samples%252FJavaEE%252FNewsAppEE6.zip">a zip archive of the finished project</a>.</li> |
| <li>Checkout the project sources from the NetBeans Samples by performing the following steps: |
| <ol> |
| <li>Choose Team > Subversion > Checkout from the main menu.</li> |
| <li>In the Checkout dialog box, enter the following Repository URL:<br/> |
| <tt>https://svn.netbeans.org/svn/samples~samples-source-code</tt><br/> |
| Click Next.</li> |
| <li>Click Browse to open the Browse Repository Folders dialog box.</li> |
| <li>Expand the root node and select <strong>samples/javaee/NewsAppEE6</strong>. Click OK.</li> |
| <li>Specify the Local Folder for the sources (the local folder must be empty).</li> |
| <li>Click Finish. |
| <p>When you click Finish, the IDE initializes the local folder as a Subversion repository |
| and checks out the project sources.</p> |
| </li> |
| <li>Click Open Project in the dialog that appears when checkout is complete.</li> |
| </ol> |
| <p class="notes"><strong>Notes.</strong></p> |
| <ul> |
| <li>You need a Subversion client to checkout the sources. |
| For more about installing Subversion, see the section on <a href="../ide/subversion.html#settingUp">Setting up Subversion</a> in the <a href="../ide/subversion.html">Guide to Subversion in NetBeans IDE</a>.</li> |
| </ul> |
| </li> |
| </ul> |
| |
| |
| |
| |
| |
| |
| <a name="Exercise_6"></a> |
| |
| <h2>Troubleshooting</h2> |
| <p>The following are some of the problems you may encounter when creating your project.</p> |
| <div class="indent"> |
| <h3 class="tutorial">Problem with JMS Resources</h3> |
| <p>When using the wizard to create JMS resources, |
| you may see the following server error message in the output window:</p> |
| <pre>[com.sun.enterprise.connectors.ConnectorRuntimeException: |
| JMS resource not created : jms/Queue] |
| </pre> |
| <p>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.</p> |
| <p>To open the Admin Console, do the following:</p> |
| <ol> |
| <li>Confirm that the application server is running by expanding the Servers node in the Services window of the IDE. |
| A small green arrow next to the application server node indicates the server is running.</li> |
| <li>Right-click the application server node and choose View Admin Console to open the login window in your browser.</li> |
| <li>Log in to the server. The default user name and password are <tt>admin</tt> and <tt>adminadmin</tt>.</li> |
| <li>In the Admin Console in your browser, expand the Resources node and JMS Resources node in the left frame.</li> |
| <li>Click on the Connection Factories and Destination Resources links in the left frame to check if the resources are |
| registered with the server and if necessary modify the resources. If the resources do not exist, you can create them |
| in the Admin Console.</li> |
| </ol> |
| <p>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 GlassFish server.</p> |
| <p>The following resources should be registered with the GlassFish server:</p> |
| <ul> |
| <li>a Destination resource with the JNDI name <tt>jms/NewMessage</tt> and type <tt>javax.jms.Queue</tt></li> |
| <li>a Connection Factory resource with the JNDI name <tt>jms/NewMessageFactory</tt> and type <tt> |
| javax.jms.QueueConnectionFactory</tt></li> |
| </ul> |
| |
| </div> |
| <br> |
| <div class="feedback-box" ><a href="/about/contact_form.html?to=3&subject=Feedback:%20Creating%20an%20Enterprise%20Application%20with%20EJB%203.1">Send Feedback on This Tutorial</a></div> |
| <br style="clear:both;" /> |
| <!-- ======================================================================================= --> |
| <h2><a name="nextsteps"></a>See Also</h2> |
| <p>For more information about using NetBeans IDE to develop Java EE applications, see the following resources: |
| </p> |
| <ul> |
| <li><a href="javaee-intro.html">Introduction to Java EE Technology</a></li> |
| <li><a href="javaee-gettingstarted.html">Getting Started with Java EE Applications</a></li> |
| <li><a href="../web/quickstart-webapps.html">Introduction to Developing Web Applications</a></li> |
| <li><a href="../../trails/java-ee.html">Java EE & Java Web Learning Trail</a></li> |
| </ul> |
| <p>You can find more information about using enterprise beans in the |
| <a href="http://docs.oracle.com/javaee/7/tutorial/doc/ejb-intro.htm">Java EE 7 Tutorial</a>.</p> |
| <p>To send comments and suggestions, get support, and keep informed on the latest |
| developments on the NetBeans IDE Java EE development features, <a href="../../../community/lists/top.html">join |
| the nbj2ee mailing list</a>.</p> |
| </body> |
| </html> |
