When running a Maven build with many plugins (e.g. the jOOQ or Flyway plugins), you may want to have a closer look under the hood to see what’s going on internally in those plugins, or in your extensions of those plugins. This may not appear obvious when you’re running Maven from the command line, e.g. via:
C:\Users\jOOQ\workspace>mvn clean install
Luckily, it is rather easy to debug Maven. In order to do so, just create the following batch file on Windows:
@ECHO OFF
IF "%1" == "off" (
SET MAVEN_OPTS=
) ELSE (
SET MAVEN_OPTS=-Xdebug -Xnoagent -Djava.compile=NONE -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=5005
)
Of course, you can do the same also on a MacOS X or Linux box, by using export intead of SET.
Now, run the above batch file and proceed again with building:
C:\Users\jOOQ\workspace>mvn_debug C:\Users\jOOQ\workspace>mvn clean install Listening for transport dt_socket at address: 5005
Your Maven build will now wait for a debugger client to connect to your JVM on port 5005 (change to any other suitable port). We’ll do that now with Eclipse. Just add a new Remote Java Application that connects on a socket, and hit “Debug”:
That’s it. We can now set breakpoints and debug through our Maven process like through any other similar kind of server process. Of course, things work exactly the same way with IntelliJ or NetBeans.
Once you’re done debugging your Maven process, simply call the batch again with parameter off:
C:\Users\jOOQ\workspace>mvn_debug off C:\Users\jOOQ\workspace>mvn clean install
And your Maven builds will no longer be debugged.
Happy debugging!
I think some of the options in your script (-Xnoagent -Djava.compile=NONE) are a bit out-of-date now – they were only needed with very old JDK versions.
The Java 7 documentation (http://docs.oracle.com/javase/7/docs/technotes/guides/jpda/conninv.html#Invocation) seemed to recommend -agentlib:jdwp over -Xrunjdwp, though the Java 8 documentation (http://docs.oracle.com/javase/8/docs/technotes/guides/jpda/conninv.html#Invocation) no longer seems to say that.
I have always used -Xdebug and -Xrunjdwp. I didn’t realise it was so complicated :-)
Interesting, thanks for pointing that out. That’s what happens when one copy-pastes blindly from old blog posts :)
Better use mvnDebug.
Perhaps – care to explain a bit more?
If you use mvnDebug there’s no need to set MAVEN_OPTS. Maven will run in debug mode and listen to port 8000
I’ll be damned. Thanks for the tip!