The Java EE 6 Tutorial, Volume I

Web Modules

In the Java EE architecture, web components and static web content files such as images are called web resources. A web module is the smallest deployable and usable unit of web resources. A Java EE web module corresponds to a web application as defined in the Java Servlet specification.

In addition to web components and web resources, a web module can contain other files:

A web module has a specific structure. The top-level directory of a web module is the document root of the application. The document root is where XHTML pages, client-side classes and archives, and static web resources, such as images, are stored.

The document root contains a subdirectory named WEB-INF, which contains the following files and directories:

If your web module does not contain any servlets, filter, or listener components then it does not need a web application deployment descriptor. In other words, if your web module only contains XHTML pages and static files, you are not required to include a web.xml file.

You can also create application-specific subdirectories (that is, package directories) in either the document root or the WEB-INF/classes/ directory.

A web module can be deployed as an unpacked file structure or can be packaged in a JAR file known as a web archive (WAR) file. Because the contents and use of WAR files differ from those of JAR files, WAR file names use a .war extension. The web module just described is portable; you can deploy it into any web container that conforms to the Java Servlet Specification.

To deploy a WAR on the Enterprise Server, the file must also contain a runtime deployment descriptor. The runtime deployment descriptor is an XML file that contains information such as the context root of the web application and the mapping of the portable names of an application’s resources to the Enterprise Server’s resources. The Enterprise Server web application runtime DD is named sun-web.xml and is located in the WEB-INF directory along with the web application DD. The structure of a web module that can be deployed on the Enterprise Server is shown in Figure 3–4.

Figure 3–4 Web Module Structure

Diagram of web module structure. WEB-INF and web pages
are under the root. Under WEB-INF are descriptors and the lib, classes, and
tags directories.

Packaging Web Modules

A web module must be packaged into a WAR in certain deployment scenarios and whenever you want to distribute the web module. You package a web module into a WAR by executing the jar command in a directory laid out in the format of a web module, by using the Ant utility, or by using the IDE tool of your choice. This tutorial shows you how to use NetBeans IDE or Ant to build, package, and deploy the sample applications.

    To build the hello2 application with NetBeans IDE, follow these instructions:

  1. Select File->Open Project.

  2. In the Open Project dialog, navigate to:

  3. Select the hello2 folder.

  4. Select the Open as Main Project check box.

  5. Click Open Project.

  6. In the Projects tab, right-click the hello2 project and select Build.

    To build the hello2 application using the Ant utility, follow these steps:

  1. In a terminal window, go to tut-install/examples/web/hello2/.

  2. Type ant. This command will spawn any necessary compilations, copy files to the tut-install/examples/web/hello2/build/ directory, create the WAR file, and copy it to the tut-install/examples/web/hello2/dist/ directory.

Deploying a WAR File

You can deploy a WAR file to the Enterprise Server in a few ways:

All these methods are described briefly in this chapter; however, throughout the tutorial, you will use ant and NetBeans IDE for packaging and deploying.

Setting the Context Root

A context root identifies a web application in a Java EE server. You specify the context root when you deploy a web module. A context root must start with a forward slash (/) and end with a string.

In a packaged web module for deployment on the Enterprise Server, the context root is stored in sun-web.xml.

    To edit the context root, do the following:

  1. Expand your project tree in the Projects pane of NetBeans IDE.

  2. Expand the Web Pages and WEB-INF nodes of your project.

  3. Double-click sun-web.xml.

  4. In the editor pane, click Edit As XML.

  5. Edit the context root, which is enclosed by the context-root element.

Deploying a Packaged Web Module

If you have deployed the hello2 application, before proceeding with this section, undeploy the application by following one of the procedures described in Undeploying Web Modules.

Deploying with the Admin Console

  1. Expand the Applications node.

  2. Click the Deploy button.

  3. Select the radio button labeled “Package file to be uploaded to the Application Server.”

  4. Type the full path to the WAR file (or click on Browse to find it), and then click the OK button.

  5. Click Next.

  6. Type the application name.

  7. Type the context root.

  8. Select the Enabled box.

  9. Click the Finish button.

Deploying with asadmin

To deploy a WAR with asadmin, open a terminal window or command prompt and execute

asadmin deploy full-path-to-war-file

Deploying with Ant

To deploy a WAR with the Ant tool, open a terminal window or command prompt in the directory where you built and packaged the WAR, and execute

ant deploy

Deploying with NetBeans IDE

    To deploy a WAR with NetBeans IDE, do the following:

  1. Select File->Open Project.

  2. In the Open Project dialog, navigate to your project and open it.

  3. In the Projects tab, right-click the project and select Deploy.

Testing Deployed Web Modules

Now that the web module is deployed, you can view it by opening the application in a web browser. By default, the application is deployed to host localhost on port 8080. The context root of the web application is hello2.

    To test the application, follow these steps:

  1. Open a web browser.

  2. Enter the following URL in the web address box:

  3. Enter your name, and click Submit.

The application should display the name you submitted.

Listing Deployed Web Modules

The Enterprise Server provides two ways to view the deployed web modules: the Admin Console and the asadmin command.

    To use the Admin Console:

  1. Open the URL http://localhost:4848/ in a browser.

  2. Expand the Applications node.

Use the asadmin command as follows:

asadmin list-components

Updating Web Modules

    A typical iterative development cycle involves deploying a web module and then making changes to the application components. To update a deployed web module, you must do the following:

  1. Recompile any modified classes.

  2. If you have deployed a packaged web module, update any modified components in the WAR.

  3. Redeploy the module.

  4. Reload the URL in the client.

Dynamic Reloading

If dynamic reloading is enabled, you do not have to redeploy an application or module when you change its code or deployment descriptors. All you have to do is copy the changed pages or class files into the deployment directory for the application or module. The deployment directory for a web module named context-root is domain-dir/applications/context-root. The server checks for changes periodically and redeploys the application, automatically and dynamically, with the changes.

This capability is useful in a development environment, because it allows code changes to be tested quickly. Dynamic reloading is not recommended for a production environment, however, because it may degrade performance. In addition, whenever a reload is done, the sessions at that time become invalid and the client must restart the session.

    To enable dynamic reloading, use the Admin Console:

  1. Select the Applications Server node.

  2. Select the Advanced tab.

  3. Check the Reload Enabled box to enable dynamic reloading.

  4. Enter a number of seconds in the Reload Poll Interval field to set the interval at which applications and modules are checked for code changes and dynamically reloaded.

  5. Click the Save button.

    In addition, to load new servlet files, do the following:

  1. Create an empty file named .reload at the root of the module:

  2. Explicitly update the .reload file’s time stamp each time you make these changes. On UNIX, execute

    touch .reload

Undeploying Web Modules

You can undeploy web modules in four ways: you can use NetBeans IDE, the Admin Console, the asadmin command, or the Ant tool.

    To use NetBeans IDE:

  1. Ensure the Enterprise Server is running.

  2. In the Services window, expand the Servers node, Enterprise Server instance and the Applications node.

  3. Right-click the application or module and choose Undeploy.

    To use the Admin Console:

  1. Open the URL http://localhost:4848/ in a browser.

  2. Expand the Applications node.

  3. Select the check box next to the module you wish to undeploy.

  4. Click the Undeploy button.

Use the asadmin command as follows:

asadmin undeploy context-root

To use the Ant tool, execute the following command in the directory where you built and packaged the WAR:

ant undeploy