Workshop

A J2EE application deployed in the WebLogic server may be debugged in the Eclipse IDE with the remote debugger provided by Eclipse. Without a debugger the error message has to be obtained from the application server error log to debug the application.

With the remote debugger provided by Eclipse, exception breakpoints may be added to the application file to debug. When an application is run in WebLogic and the application generates an error, the application gets suspended and the Eclipse IDE Debug perspective displays the error. In this tutorial we will debug a WebLogic Application Server application in Eclipse.

To debug an application deployed in the WebLogic Server from Eclipse, start the WebLogic Server in debug mode and configure a remote debugging configuration in Eclipse. Next, connect the Eclipse remote debugger to the WebLogic Server and debug applications running in the server. We will develop an example servlet application and deploy the application in WebLogic. First, the servlet is run without any error and subsequently an error is introduced in the servlet to demonstrate the remote debugging feature in Eclipse.

Preliminary Setup
Download the WebLogic 8.1 Application Server and install it. Download the Eclipse 3.0 or Eclipse 3.02 zip file eclipse-SDK-3.0-win32.zip (www.eclipse.org/downloads/index.php) and install it as well.

Developing a WebLogic Application
After installing the WebLogic Server and the Eclipse IDE, develop a servlet application to run and debug in the WebLogic Server. The example servlet application consists of a doGet method, which prints out a String message to the browser. The example servlet, WebLogicServlet.java, is shown in Listing 1.

Create a directory structure for a Web application. Create a WEB-INF directory and a classes directory in the WEB-INF directory. Create a package directory servlets for the example servlet and copy the WebLogicServlet.java file to the servlets directory. Create a web.xml deployment descriptor for the Web application. Copy the web.xml file to the WEB-INF directory. Listing 2 shows the web.xml file.

The example servlet is mapped to URL pattern /weblogic. The structure of the Web application is illustrated below.

     /WEB-INF
      |      |
   web.xml classes
                 |
                 servlets
                      |
                     WebLogicServlet.class

The compiling, packaging, and deploying of the Web application is done in the Eclipse IDE with an Ant build.xml file. Develop an Ant build.xml file that consists of targets to compile the WebLogicServlet.java and package and deploy the webapp.war Web application. Listing 3 shows the build.xml file.

Table 1 shows the properties of the build.xml file. Table 2 shows the file's targets.

Set the debug attribute of the javac task in the build target to true to enable compilation in debug mode. By compiling an application in debug mode the line number, which generates the exception in a WebLogic Server application, gets displayed in the Debug perspective. Create a new project in the Eclipse IDE. Select File>New>Project. The New Project frame gets displayed. In the New Project wizard select Java>Java Project. Click on the Next button. The New Java Project frame gets displayed. In the New Java Project frame specify a Project Name, EclipseWebLogic for example, and click on the Next button. In the Java Settings frame add a source folder to the project with the Add Folder button.

The New Source Folder frame gets displayed. In the New Source Folder frame specify a folder name, src for example. A source folder gets added to the project. A message prompt gets displayed to update the source folder and the output folder. In the New Java Project frame click on the Finish button to create the project. A new project gets added to the Eclipse IDE. Next, select File>Import to import the example servlet source folder to the project. In the Import Select frame select File System and click on the Next button. In the Import File System frame select the src folder and the build.xml file and then click on the Finish button. The servlet source files get added to the project.

Run the build.xml file to compile, package, and deploy the servlet Web application to the WebLogic Server. Right-click on the build.xml file and select Run>Ant Build. The Web application .war file webapp.war gets generated and is deployed to the WebLogic 8.1 Application Server applications directory. Next, start the WebLogic Server with the bin/run script. Invoke the example servlet in a Web browser with the URL http://localhost:7001/webapp/weblogic. The WebLogicServlet runs in the WebLogic Server and the output gets displayed in the browser.

Configuring a Remote Debugging Configuration in Eclipse
To remote debug a WebLogic application in Eclipse start the WebLogic Server in debug mode. Set the WebLogic Server in debug mode by setting the debug options in the startWebLogic batch script file. The debugging provided by WebLogic is based on the Java Platform Debugger Architecture (JPDA). Set the JAVA_OPTS variable as:

set JAVA_OPTS= -Xdebug -Xnoagent
-Xrunjdwp:transport=dt_socket,address=8787,server=y,suspend=n %JAVA_OPTS%

Table 3 shows the different debug parameters. For further explanation of the debug settings refer to the JPDA documentation (http://java.sun.com/j2se/1.4.2/docs/guide/jpda/). To demonstrate the remote debugging feature of Eclipse, add an exception to the WebLogicServlet.java file. For example, add a NullPointerException to the WebLogicServlet.java class. Replace

out.println("Eclipse WebLogic Remote Debugging");

with

String str=null;
out.println(str.toString());

Next, configure a debug configuration for the Eclipse project. Select the Debug option in the Debug option list. The Debug frame gets displayed. In the Debug frame select the Remote Java Application node. Right-click on the node and select New. In the Debug configuration frame specify a name for the Debug configuration. Select the project that is to be debugged. Select the EclipseWebLogic project previously created in the Eclipse IDE. Select the default value for Connection Type. In the Connection Properties, specify localhost as the Host and specify the Port as the port that was specified in the startWebLogic batch script of the WebLogic server, 8787. Click on the Apply button. A remote Java application debug configuration gets added.

Next add exception breakpoints to the WebLogicServlet.java file. To demonstrate the remote debug feature of Eclipse a NullPointerException was added to the WebLogicServlet.java file earlier in this section. To add a breakpoint to the servlet class, Select Run>Add Java Exception Breakpoint. In the Add Java Exception Breakpoint frame select the NullPointerException. The NullPointerException breakpoint gets added to the servlet class. If a NullPointerException is generated in the servlet application in the WebLogic Server, the application gets suspended and the Debug perspective of the Eclipse IDE displays the exception.

Remote Debugging a WebLogic Application
After configuring a debug configuration for the example servlet application deployed in the WebLogic Server, we will debug the servlet application in the Eclipse IDE. Create a webapp.war Web application from the modified (with the NullPointerException) WebLogicServlet.class file with the build.xml file as explained in the "Developing a WebLogic Application" section. Start the WebLogic Server. The server starts in debug mode with the debug options specified in the startWebLogic batch file.

Next, select the EclipseDebug debug configuration in the Debug frame. Click on the Debug button to connect the remote debugger to the WebLogic Server. The Eclipse remote debugger gets connected to the WebLogic Server. Select the Debug Perspective button to display the debug perspective of the Eclipse IDE. In the Debug perspective the remote debugger is shown connected to the WebLogic server at localhost, port 8787. Access the WebLogicServlet in the WebLogic Server with the URL http://localhost:7001/webapp/weblogic. Because the servlet has a NullPointerException, the servlet gets suspended with a NullPointerException in the Debug perspective. The line that produced the exception gets displayed.

The line that throws the exception is the out.println(str.toString()); code line. The servlet application may be debugged with the different debug options listed by selecting Run in the Eclipse IDE.

Summary
In this tutorial a WebLogic application was debugged in the Eclipse IDE. A WebLogic application may also be debugged from another IDE such as JDeveloper.