Trace Levels

At the heart of most logging packages is the notion of different levels of messages. By sorting your application's messages into these different levels, you can provide different levels of detail. Depending on the specific logging toolkit in use, you might route certain messages to System.out or to a file on disk and simply ignore others.

Logging defines several different logging levels, as shown in Table 9-1, in order of severity.

Table 9-1. Logging Levels

Logging Level	Meaning	Corresponding Level JDK 1.4 Level
fatal	Severe errors that cause premature termination. Expect these to be immediately visible on a status console.	SEVERE
error	Other runtime errors or unexpected conditions. Expect these to be immediately visible on a status console.	SEVERE
warn	Use of deprecated APIs, poor use of an API, and other runtime situations that are undesirable or unexpected but that don't necessarily represent an application failure. Expect these to be immediately visible on a status console.	WARNING
info	Interesting runtime events (startup/shutdown). Expect these to be immediately visible on a console, so be conservative and keep them to a minimum.	INFO
debug	Detailed information on the flow of the system. Expect these to be written to logs only.	FINE
trace	Even more detailed information than a debug trace. Expect these to be written to logs only.	FINEST