The Java Debugger

The Java Debugger (jdb) is a dynamic, controlled, assignment-based
debugging tool. It helps find and fix bugs in the Java language
programs both locally and on the server. To use jdb in a J2EE
application server you must first launch it with debugging enabled and
attach to the server from the debugger through a JPDA port (Default
port is 1044).

The default JPDA options for J2EE servers are as follows:

-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=1044

The jdb parameters specify the way debugger will operate. For instance transport=dt_socket instructs the JVM that the debugger connections will be made through a socket while the address=1044 parameter informs it that the port number will be 1044. Similarly, if you substitute suspend=y ,
the JVM starts in suspended mode and stays suspended until a debugger
is attached to it. This may be helpful if you want to start debugging
as soon as the JVM starts.

Debugging WebLogic

Debugging WebLogic is no different than debugging any other Java
remote application. You need to make sure to launch it with the
required debugging arguments and attach a debugger. In the case of
WebLogic 8.1, you need to add these arguments to the startup script.
WebLogic comes with several launch scripts (*.sh and *.cmd) under
BEA_HOME/weblogic81/server/bin.

1. Locate startWSL.cmd and add the following variable DEBUG_OPTS:

   set DEBUG_OPTS = -Xdebug -Xrunjdwp:transport= dt_socket,address=1044,server=y,suspend=n
   

2. Next, insert the new variable to the WebLogic startup command,
   after "%JAVA_HOME%/bin/java" and preferably before the other options.
3. Your startup script should look like:
   "%JAVA_HOME%/bin/java"
   %DEBUG_OPTS% %JAVA_VM% %MEM_ARGS%
   %JAVA_OPTIONS%-Dweblogic.Name=%SERVER_NAME%
   -Dweblogic.management.username=
   %WLS_USER%-Dweblogic.management.password= %WLS_PW%
   -Dweblogic.management.server=
   %ADMIN_URL%-Dweblogic.ProductionModeEnabled=
   %PRODUCTION_MODE%-Djava.security.policy=
   "%WL_HOME%/server/lib/weblogic.policy" weblogic.Server

Debugging JBoss

Same as WebLogic, except that you need to change run.bat/run.sh located under JBOSS_HOME/bin.

Linux users should see something similar to this:

 $ cd /var/jboss4/bin
 $ sh ./run.sh 
 =========================================================================

 JBoss Bootstrap Environment

 JBOSS_HOME: /var/jboss4

 JAVA: /usr/java/j2sdk1.4.2_06/bin/java

 JAVA_OPTS: -server -Xms128m -Xmx128m -Dprogram.name=run.sh

 DEBUG_OPTS = -Xdebug -Xrunjdwp:transport= dt_socket,address=1044,server=y,suspend=n

 CLASSPATH: /var/jboss4/bin/run.jar:/usr/java/j2sdk1.4.2_06/lib/tools.jar

 =========================================================================

Debugging Tomcat

Again, very much similar to WebLogic and JBoss, except that you need
to change catalina.bat/catalina.sh located under TOMCAT_HOME/bin.

Debugger Verification

Now you can launch your application in debug mode. Just to make sure
that the server is listening to port 1044 you can run netstat /a. You
should see port 1044 in the list of open ports (See Figure 1: List of
open ports: netstat -a).

Figure 1 List of open ports: netstat -a

The Eclipse Connection

After making sure WebLogic is listening for incoming connections on
port 1044, what is left is to tell Eclipse to connect to this port and
you are ready to debug.

1. In Eclipse, navigate to Run | Debug (See Figure 2: Create new Remote Java Application configuration in Eclipse ).
2. Select Remote Java Application , on the left column. Click New , on the bottom of the same column.
3. In the Create configuration screen you'll be prompted to enter some values. Start with a meaningful name. In my case that's WebLogic Instance . For Project, select the Java project that contains the source code you want to debug. Leave Connection Type in default, i.e. Standard (Socket Attach) . For Host , enter localhost. If you want to debug a remote server, enter its hostname or IP address. For port, enter 1044 or the port you defined in your WebLogic startup script.
4. Click Apply
5. Make sure WebLogic instance is running in debug mode. In the same screen click Debug . Eclipse should automatically take you to the Debug perspective and you should see a stack trace in the Debug view.
6. If you are not automatically taken to the Debug perspective, select Window | Open Perspective | Other and then click Debug.

Figure 2 Create new Remote Java Application configuration in Eclipse
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Eclipse Debug window should automatically pop-up with the stack pointer on your first breakpoint (See Figure 3: Breakpoint hit in Eclipse's debugger ).
After that, you can use all the various functions that the debugger has
to offer, namely variable assignments, step-into, drop to frame, etc.

Figure 3 Breakpoint hit in Eclipse debugger