How can I debug a Java Google App Engine app in IDEA while using the GAE Maven plugin?

Question

I have set up my pom.xml like so, and it appears to be working for the most part, I can start the devserver and update the application.

My problem is that I can't seem to debug the devserver. I tried launching the devserver maven goal in debug mode from within IDEA, but when I set breakpoints they are ignored.

I found in the GAE Maven plugin docs that you can launch the devserver in debug mode with the following configuration:

<jvmFlags>
  <jvmFlag>-Xdebug</jvmFlag>
  <jvmFlag>-agentlib:jdwp=transport=dt_socket,address=8000,server=y,suspend=n</jvmFlag>
</jvmFlags>

However I don't know how to tell IDEA to connect the debugger when I start the Maven Run/Debug configuration.

Can anyone point me in the right direction?

Answer 1

The configuration mentioned in your question looks good. So, you have:

<jvmFlags>
  <jvmFlag>-Xdebug</jvmFlag>
  <jvmFlag>-agentlib:jdwp=transport=dt_socket,address=8000,server=y,suspend=n</jvmFlag>
</jvmFlags>

1. When you run your Maven build

   mvn appengine:devserver
   

   at some point it halts and waits for the remote debugger to connect.

2. In IDEA, go to Run > Edit Configurations... and add a new Remote configuration.

3. Give it a name and check parameters (especially the port).
4. Click OK
5. Run the debugger with Run > Debug '<name of your config>' (Shift-F9)