Java snippet: Debugging a Java library used from Ant
I recently needed to debug a library which seemed to be misbehaving when used within Ant. After a bit of research here’s the best way I found to debug within Ant that doesn’t require sprinkling your bin/ant or bin\ant.bat with temporary JPDA pixy dust.
Ant doesn’t directly accept the -X arguments needed to set up the JPDA settings so the question is: how do you pass these from a shell or command line? In this, the ANT_OPTS environment variable is your friend. Its contents will be directly passed to the Java process Ant calls.
So here’s how you do it:
Step 1: Set ANT_OPTS to the debug options appropriate for your JVM:
for Java 1.4:
>> export ANT_OPTS=-Xdebug -Xnoagent -Djava.compiler=NONE -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8453
for Java 1.5:
>> export ANT_OPTS=-agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=8453
Step 2: Run ant like normal:
>> ant
Step 3: Set your breakpoints.
Step 4: Now attach your debugger.
There might be better ways to do this but this was the least invasive route for me.
