how do you debug java annotation processors using intellij?

Question

How do you debug java annotation processors using intellij?

Preferably using IDEA IntelliJ. I tried setting a breakpoint inside the processor and running but it did not break.

Answer 1

If you really need to debug an annotation processor, it might be better to run the annotation processor from the command line rather than within your IDE with debugging enabled and attach to that using your IDE's debugger.

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If running javac directly, you can debug this by specifying the following extra parameters:

javac -J-Xdebug -J-Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8000 ... (usual javac parameters go here) 

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If running Maven, use mvndebug instead of the standard mvn command - Maven runs the compiler in-process.

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If running Ant, add the following to the ANT_OPTS environment variable before running:

-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8000 

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With all these executions, the javac, Ant or Maven process will wait for you to attach your debugger before it actually starts executing. IntelliJ instructions for this are here. For Eclipse, here.

Answer 2

This tutorial is written for an Android project. Main module name is "app" as usual. The project contains a submodule called "annotation" which is subdependency of "app". "app" module runs annotation processing with gradle declaration apt project(':annotation') .

SIMPLE VERSION (run compilation from terminal and attach from IDE)

1. [REQUIRED] Add a new project configuration "+" -> "Remote". Check "Single instance only". All other settings are generated automatically. Leave <whole project> as the classpath. Port should be left as the default 5005.

2. [REQUIRED] Make sure you stop all gradle instances by calling: ./gradlew --stop
3. [REQUIRED] Run the command : ./gradlew --no-daemon -Dorg.gradle.debug=true :app:clean :app:compileDebugJavaWithJavac

4. Run the APT project configuration in debug mode as fast as possible :)

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4. [HINT] We start with an EMPTY gradle.properties file
5. [HINT] DO NOT USE gradle daemon ( --no-daemon / org.gradle.daemon=false option )
6. [HINT] Run gradle in debug mode ( org.gradle.debug=true option )
7. [HINT] Run app's module compilation not the processor's module compilation (app's compilation runs annotation processing!)
8. We DO NOT normally add any Java compiler settings in Android Studio (i.e. File -> other settings -> Default settings)

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EXTENDED VERSION (use gradle.properties)

1. Add the following to your gradle.properties file:

      org.gradle.daemon=false     org.gradle.debug=true  

2. Run the compilation from terminal:

./gradlew :app:clean :app:compileDebugJavaWithJavac

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ADVANCED VERSION (just press debug in IDE)

1. Add a bash script to your project main dir (e.g. compile.sh)

 #!/bin/bash ./gradlew :app:clean :app:compileDebugJavaWithJavac & 

Remember about the '&' sign for background processing.

2. Go to APT configuration settings we created in step 1 and add a Before launch configuration. Select Run external tool.

3. Add the path to the compile.sh script we created earlier.

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Warning

Messing up gradle compilation, NullPointer exceptions during compilation etc. sometimes result in AndroidStudio being stuck (frozen on gradle refresh stage). If you cannot stop gradle from the IDE then use this command in the terminal:

ps -A | grep gradle | awk '{ print $1; }' | xargs kill -9 

Turning off debug option during project refresh sometimes helps Android Studio to come back to the right track.