Debug Jetty in Maven started by mvn jetty:run
Set environment variable MAVEN_OPTS to:
-Xdebug -Xnoagent -Djava.compiler=NONE -Xrunjdwp:transport=dt_socket,address=8000,server=y,suspend=n
Then in Eclipse 3 click Run > Debug Configurations > create New Remote Java Application. Remember to attach sources. Invoke Maven by mvn jetty:run
and start Debug in Eclipse.