The Java EE 7 Tutorial

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36.2 The async Example Application

The async example demonstrates how to define an asynchronous business method on a session bean and call it from a web client. This example contains two modules.

  • A web application (async-war) that contains a stateless session bean and a JavaServer Faces interface. The MailerBean stateless session bean defines an asynchronous method, sendMessage, which uses the JavaMail API to send an email to an specified email address.

  • An auxiliary Java SE program (async-smtpd) that simulates an SMTP server. This program listens on TCP port 25 for SMTP requests and prints the email messages to the standard output (instead of delivering them).

The following section describes the architecture of the async-war module.

36.2.1 Architecture of the async-war Module

The async-war module consists of a single stateless session bean, MailerBean, and a JavaServer Faces web application front end that uses Facelets tags in XHTML files to display a form for users to enter the email address for the recipient of an email. The status of the email is updated when the email is finally sent.

The MailerBean session bean injects a JavaMail resource used to send an email message to an address specified by the user. The message is created, modified, and sent using the JavaMail API. The session bean looks like this:

@Named
@Stateless
public class MailerBean {
    @Resource(name="mail/myExampleSession")
    private Session session;
    private static final Logger logger = 
            Logger.getLogger(MailerBean.class.getName());

    @Asynchronous
    public Future<String> sendMessage(String email) {
        String status;
        try {
            Message message = new MimeMessage(session);
            message.setFrom();
            message.setRecipients(Message.RecipientType.TO,
                    InternetAddress.parse(email, false));
            message.setSubject("Test message from async example");
            message.setHeader("X-Mailer", "JavaMail");
            DateFormat dateFormatter = DateFormat
                    .getDateTimeInstance(DateFormat.LONG, DateFormat.SHORT);
            Date timeStamp = new Date();
            String messageBody = "This is a test message from the async "
                    + "example of the Java EE Tutorial. It was sent on "
                    + dateFormatter.format(timeStamp)
                    + ".";
            message.setText(messageBody);
            message.setSentDate(timeStamp);
            Transport.send(message);
            status = "Sent";
            logger.log(Level.INFO, "Mail sent to {0}", email);
        } catch (MessagingException ex) {
            logger.severe("Error in sending message.");
            status = "Encountered an error: " + ex.getMessage();
            logger.severe(ex.getMessage());
        }
        return new AsyncResult<>(status);
    }
}

The injected JavaMail resource can be configured through the GlassFish Server Administration Console, through a GlassFish Server administrative command, or through a resource configuration file packaged with the application. The resource configuration can be modified at runtime by the GlassFish Server administrator to use a different mail server or transport protocol.

The web client consists of a Facelets template, template.xhtml; two Facelets clients, index.xhtml and response.xhtml; and a JavaServer Faces managed bean, MailerManagedBean. The index.xhtml file contains a form for the target email address. When the user submits the form, the MailerManagedBean.send method is called. This method uses an injected instance of the MailerBean session bean to call MailerBean.sendMessage. The result is sent to the response.xhtml Facelets view.

36.2.2 Running the async Example

You can use either NetBeans IDE or Maven to build, package, deploy, and run the async example.

36.2.2.1 To Run the async Example Application Using NetBeans IDE

  1. Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).

  2. From the File menu, choose Open Project.

  3. In the Open Project dialog box, navigate to:

    tut-install/examples/ejb
    
  4. Select the async folder, select Open Required Projects, and click Open Project.

  5. In the Projects tab, right-click the async-smtpd project and select Run.

    The SMTP server simulator starts accepting connections. The async-smptd output tab shows the following message:

    [Test SMTP server listening on port 25]
    
  6. In the Projects tab, right-click the async-war project and select Build.

    This command configures the JavaMail resource using a GlassFish Server administrative command and builds, packages, and deploys the async-war module.

  7. Open the following URL in a web browser window:

    http://localhost:8080/async-war
    
  8. In the web browser window, enter an email address and click Send email.

    The MailerBean stateless bean uses the JavaMail API to deliver an email to the SMTP server simulator. The async-smptd output window in NetBeans IDE shows the resulting email message, including its headers.

  9. To stop the SMTP server simulator, click the X button on the right side of the status bar in NetBeans IDE.

  10. Delete the JavaMail session resource.

    1. In the Services tab, expand the Servers node, then expand the GlassFish 4.0 server node.

    2. Expand the Resources node, then expand the JavaMail Sessions node.

    3. Right-click mail/myExampleSession and select Unregister.

36.2.2.2 To Run the async Example Application Using Maven

  1. Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).

  2. In a terminal window, go to:

    tut-install/examples/ejb/async/async-smtpd/
    
  3. Enter the following command to build and package the SMTP server simulator:

    mvn install
    
  4. Enter the following command to start the STMP server simulator:

    mvn exec:java
    

    The following message appears:

    [Test SMTP server listening on port 25]
    

    Keep this terminal window open.

  5. In a new terminal window, go to:

    tut-install/examples/ejb/async/async-war
    
  6. Enter the following command to configure the JavaMail resource and to build, package, and deploy the async-war module:

    mvn install
    
  7. Open the following URL in a web browser window:

    http://localhost:8080/async-war
    
  8. In the web browser window, enter an email address and click Send email.

    The MailerBean stateless bean uses the JavaMail API to deliver an email to the SMTP server simulator. The resulting email message appears on the first terminal window, including its headers.

  9. To stop the SMTP server simulator, close the terminal window in which you issued the command to start the STMP server simulator.

  10. To delete the JavaMail session resource, type the following command:

    asadmin delete-javamail-resource mail/myExampleSession
    
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