How to debug Java EE on JBossAS

A week ago I noticed a problem with a strange behavior of an EJB component.

Source code inspecting was not enough to understand what was happening. So I had to debug the component. In that moment I remembered what I felt the first time when I had to do a debug on such kind of application. I supposed that should be a complicated process behind, that I was needed some sophisticated tool for that. In reality the task is very easy to accomplish. Even the title of this article is misleading. You will understand why.

Java virtual machine gives us the everything to do a remote debug on any kind of Java application. Simply, as long as we have the source code, we can debug anything on the local computer or on the network. JBossAS is a Java application itself, like any other. Ok, not like any other, but from this point of view there is not difference.

Taking thisn into consideration, all we have to do is to configure the virtual machine on which the JBossAS is running. We have to enable a TCP connection for remote debugging, to enable the required port in firewall and to connect our IDE to that port. We need to have an IDE which is able to do a remote debugging, but virtually all the IDEs on the market implement that feature.

Configuring JBossAS

JBossAS make things simpler, from this point of view. If you use Linux, you should modify run.conf, if on Windows, you should modify directly run.bat (don't have any clue why on Windows they don't use run.conf). Here are the lines which should be modified.

# Sample JPDA settings for remote socket debuging
#JAVA_OPTS="$JAVA_OPTS -Xrunjdwp:transport=dt_socket,address=8787,server=y,suspend=n"

If have only to remove the comment sign on the second line. We can change the port as we wish (TCP is used). Default value for that is 8787. The suspend deserves a closer look. If we change the value to y, that, the debugged process will wait for the client to make a remote connection and after that will continue to run. This is very useful if we have to debug something in the initializing code of the target application. Now is not useful.

I repeat, this kind of debugging can be enabled on any Java process. In that case this options are give in the command line to the java runtime.

Network configuration

If the target process is executed on another computer we should be able to connect on that machine. In order to be able to do this the specified port should not be blocked by firewall, if we have something like this enable. If the target system is not in our network or we don't have direct acces on that, than we have to create a path to that port. We do that using routing and port forwarding. Eventually from computer to computer until we found one which we can connect to.

Starting a remote debug session from Eclipse

In Ecplise we use menu item Run -> Debug Configurations .. It will open a dialog box with execution configuration. We create a configuration for Remote Java Application. There we specify the project which contains the sources we want to debug, the host name or ip of the target system and the port, also.

Eventually we configure the breakpoints we want and .. happy debugging!