kotlin: Debugging SpringBoot with jdb

If you start the gradle application with a special flag, --debug-jvm, then jdb can connect.

# Start JVM task via gradle, expecting debugger
./gradlew bootRun --debug-jvm
# ... blocks, waiting for debugger to attach

# In another session, attach
jdb -attach 5005 -sourcepath src/main/kotlin/
# OR even better, use rlwrap to improve the jdb prompt
rlwrap jdb -attach 5005 -sourcepath src/main/kotlin/

Note that the -sourcepath command specifies where the convention based class naming convention starts.

Using jdb

• Add a breakpoint: stop at com.foo.bar.ClassName.methodName
• Remove a breakpoint: clear com.foo.bar.ClassName.methodName
• Show source lines for current point: list
• Show stack trace for current point: where
• Start process running: run
• Step into next command: step
• Step over next command: next
• Get help: help

Gotchas

• The raw jdb prompt is rubbish i.e. no readline. Consider rlwrap
• Watch for nested class naming convention, com.foo.Class$Nested