Java logging or logging in java is as much an art as science. knowing to write tools and API for java logging is definitely the science part but choosing the format of java logs, the format of messages, what to log in to java, which logging level to use for which kind of messages are purely experienced-based things, and sort of art which you learn by applying logging in java. Since its proven fact that java logging severely affects performance and I have seen latency of online stock trading application goes multiple times if they run in DEBUG mode than in WARN or higher level mode.