gui4j uses Jakarta Commons Logging as its logging API. In your project you should therefore initialize a compatible logging framework. Experiment with different log levels to see what is being logged. In normal operations, you will usually use WARN or INFO.
When creating your Gui4j instance via the Gui4jFactory, you must supply a parameter that defines if method invocations from the frameworks into your controllers should be logged. You can set this parameter to true in order to debug problems related to method calls. Due to the number of log messages produced, you should set this parameter to false in production environments.
If you get a stacktrace caused by a gui4j worker thread, you will possibly want to know which gui4j method call caused the worker thread to run. To get this additional information in case of an internal gui4j error, you can call Gui4j.setTraceWorkerInvocation(true). This can be a great help in debugging. Don’t turn this feature on in production, since the internal overhead of creating a stacktrace for each worker invocation might be high.