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 somewhe

Answer 1

If you don't want to be IDE dependent and want to work directly with the command line, you can use 'jdb' (Java Debugger)

As mentioned by Samuel with small modification (set suspend=y instead of suspend=n, y means yes which suspends the program and not run it so you that can set breakpoints to debug it, if suspend=n means it may run the program to completion before you can even debug it)

On the directory which contains your pom.xml, execute:

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

Then, open up a new terminal and execute:

jdb -attach 1044

You can then use jdb to debug your program!=)

Sources: Java jdb remote debugging command line tool

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 Netbeans, there is a nice shortcut to this. Just define a goal exec:java and add the property jpda.listen=maven

Tested on Netbeans 7.3

Answer 4

I found an easy way to do this -

Just enter a command like this -

>mvn -Dtest=TestClassName#methodname -Dmaven.surefire.debug test

It will start listening to 5005 port. Now just create a remote debugging in Eclipse through Debug Configurations for localhost(any host) and port 5005.

Source - https://doc.nuxeo.com/display/CORG/How+to+Debug+a+Test+Run+with+Maven

Answer 5

I thought I would expand on these answers for OSX and Linux folks (not that they need it):

I prefer to use mvnDebug too. But after OSX maverick destroyed my Java dev environment, I am starting from scratch and stubbled upon this post, and thought I would add to it.

$ mvnDebug vertx:runMod
-bash: mvnDebug: command not found

DOH! I have not set it up on this box after the new SSD drive and/or the reset of everything Java when I installed Maverick.

I use a package manager for OSX and Linux so I have no idea where mvn really lives. (I know for brief periods of time.. thanks brew.. I like that I don't know this.)

Let's see:

$ which mvn
/usr/local/bin/mvn

There you are... you little b@stard.

Now where did you get installed to:

$ ls -l /usr/local/bin/mvn

lrwxr-xr-x  1 root  wheel  39 Oct 31 13:00 /
                  /usr/local/bin/mvn -> /usr/local/Cellar/maven30/3.0.5/bin/mvn

Aha! So you got installed in /usr/local/Cellar/maven30/3.0.5/bin/mvn. You cheeky little build tool. No doubt by homebrew...

Do you have your little buddy mvnDebug with you?

$ ls /usr/local/Cellar/maven30/3.0.5/bin/mvnDebug 
/usr/local/Cellar/maven30/3.0.5/bin/mvnDebug

Good. Good. Very good. All going as planned.

Now move that little b@stard where I can remember him more easily.

$ ln -s /usr/local/Cellar/maven30/3.0.5/bin/mvnDebug /usr/local/bin/mvnDebug
  ln: /usr/local/bin/mvnDebug: Permission denied

Darn you computer... You will submit to my will. Do you know who I am? I am SUDO! BOW!

$ sudo ln -s /usr/local/Cellar/maven30/3.0.5/bin/mvnDebug /usr/local/bin/mvnDebug

Now I can use it from Eclipse (but why would I do that when I have IntelliJ!!!!)

$ mvnDebug vertx:runMod
Preparing to Execute Maven in Debug Mode
Listening for transport dt_socket at address: 8000

Internally mvnDebug uses this:

MAVEN_DEBUG_OPTS="-Xdebug -Xnoagent -Djava.compiler=NONE  \
-Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8000"

So you could modify it (I usually debug on port 9090).

This blog explains how to setup Eclipse remote debugging (shudder)

http://javarevisited.blogspot.com/2011/02/how-to-setup-remote-debugging-in.html

Ditto Netbeans

https://blogs.oracle.com/atishay/entry/use_netbeans_to_debug_a

Ditto IntelliJ http://www.jetbrains.com/idea/webhelp/run-debug-configuration-remote.html

Here is some good docs on the -Xdebug command in general.

http://docs.oracle.com/cd/E13150_01/jrockit_jvm/jrockit/jrdocs/refman/optionX.html

"-Xdebug enables debugging capabilities in the JVM which are used by the Java Virtual Machine Tools Interface (JVMTI). JVMTI is a low-level debugging interface used by debuggers and profiling tools. With it, you can inspect the state and control the execution of applications running in the JVM."

"The subset of JVMTI that is most typically used by profilers is always available. However, the functionality used by debuggers to be able to step through the code and set breakpoints has some overhead associated with it and is not always available. To enable this functionality you must use the -Xdebug option."

-Xrunjdwp:transport=dt_socket,server=y,suspend=n myApp

Check out the docs on -Xrunjdwp too. You can enable it only when a certain exception is thrown for example. You can start it up suspended or running. Anyway.. I digress.

Answer 6

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.