Jetty has it's own builtin logging facade that can log to stderr or slf4j (which in turn can log to commons logging, log4j, nlog4j and java logging).
Jetty logging looks for a slf4j jar on the classpath. If found, slf4j is used to control logging otherwise stderr is used. The org.mortbay.log.Log class is used to coordinate logging and the following system parameters may be used to control logging:
Specify an implementation of org.mortbay.log.Logger to use
If set, debug logs will be produced, else only INFO and WARN logs will be generated
If set, verbose logging is produced, including ignored exceptions
If set (jetty 6.1.10 and later), ignored exceptions are logged (independent of DEBUG and VERBOSE settings
With Jetty Standalone
The core of Jetty has no hard dependencies on an external logging infrastructure. The only logging dependency is introduced by Jasper, the JSP engine.