Debugging a plugin
With help of the Maven HPI Plugin Jenkins plugins can be started in a local Jenkins sandbox.
For debugging purposes run following Maven command from plugin project directory:
mvn hpi:run
By default, the debugging instance is then available at http://localhost:8080/jenkins in your browser.
In order to launch Jenkins on a different port than 8080 use this system property:
mvn hpi:run -Djetty.port=8090
Changing the default context path can be achieved by setting this system property:
mvn hpi:run -Dhpi.prefix=/debug
Debugging from IDE
Starting a debug session from your IDE requires to set special Maven options:
MAVEN_OPTS="-Xdebug -Xrunjdwp:transport=dt_socket,server=y,address=8000,suspend=n"
This allows to hook into the instance and set break points while being in IDE debugging mode.
Changing code while debugging is supported for Jelly/Groovy views, properties and help files with simple page reload in the browser. Utilizing from JVM's hot swap feature does not support changing method signatures. Changes in pom.xml also requires to restart the debugging process.