The Wrapper contains support for requesting that the JVM dump out its current state. The exact contents of the information will vary depending on which JVM is being run.

The Sun JVMs will display the stack traces of all running threads to the console.

IBM JVMs provide even more useful information. The stack traces of all threads as well as object monitor states are dumped to the console. In addition a file is created in the current directory which in addition to the information shown in the console also contains useful information about the system including all of the environment variables.

A Thread Dump can be requested on Windows systems by pressing CTRL-BREAK or on Linux systems by pressing CTRL-\. Invoking a thread dump does not affect the JVM. It will continue to run normally.

The startup for Linux and Solaris provided with the Wrapper installation, launch the Wrapper in a background thread. To request a thread dump using these scripts, simply rerun the script specifying the 'dump' parameter.

Many configuration problems can be quickly resolved by setting the log level of the console output to DEBUG. The full command used to launch Java as well as version information on the JVM being run will then be displayed in the console. See the Logging Configuration Properties section for more information.

Another usefull Debugging technique worked well for me:

Step one: Configure the JVM in the propertiesfile to listen on a remotedebugging port:

# Java Additional Parameters for debugging
wrapper.java.additional.1=-Xdebug
wrapper.java.additional.2=-Xnoagent
#wrapper.java.additional.3=-Xrunjdwp:transport=dt_socket,server=y,address=8000,suspend=n
# or:
wrapper.java.additional.3=-Xrunjdwp:transport=dt_socket,server=y,address=8000,suspend=y

If you enable suspend, the JVM stops and waits for a connection before the serviceapplication starts. If you disable it, the service/application runs normal until a debug client connects and sends breakpoints.

Step two: Connect with your favourite debug client (eclipse in my case) and start debugging.