Debugging in Maven?

Question

Is it possible to launch a debugger such as jdb from maven? I have a pom.xml file that compiles the project successfully. However, the program hangs somewhere and I would really like to launch jdb or an equivalent debugger to see what's happening.

I compile using mvn compile and launch using:
mvn exec:java -Dexec.mainClass="com.mycompany.app.App"

I was expecting something like:
mvn exec:jdb -Dexec.mainClass="com.mycompany.app.App"
to launch the debugger but, as usual, my expectations are incongruent with maven's philosophy.

Also, I couldn't find any documentation (on Maven's website or google) to describe how debugging works. I suspect that I have to use some plugin.

Answer 1

Why not use the JPDA and attach to the launched process from a separate debugger process ? You should be able to specify the appropriate options in Maven to launch your process with the debugging hooks enabled. This article has more information.

Answer 2

Just as Brian said, you can use remote debugging:

mvn exec:exec -Dexec.executable="java" -Dexec.args="-classpath %classpath -Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=1044 com.mycompany.app.App"

Then in your eclipse, you can use remote debugging and attach the debugger to localhost:1044.

Answer 3

If you are using Maven 2.0.8+, run the mvnDebug command in place of mvn and attach a debugger on port 8000.

For Maven <2.0.8, uncomment the following line in your %M2_HOME%/bin/mvn.bat (and maybe save the modified version as mvnDebug.bat):

@REM set MAVEN_OPTS=-Xdebug -Xnoagent -Djava.compiler=NONE -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8000

More details in MNG-2105 and Dealing with Eclipse-based IDE.

Answer 4

I use the MAVEN_OPTS option, and find it useful to set suspend to "suspend=y" as my exec:java programs tend to be small generators which are finished before I have manage to attach a debugger.... :) With suspend on it will wait for a debugger to attach before proceding.