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

User · Answer

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  lt 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

User · Answer

I found an easy way to do this -  Just enter a command like this -   gt 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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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 - gt   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

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