log4j is possibly the most popular Java logging solution. Logging is done onto a virtual medium, which may then be reconfigured at run time to route messages from particular components and of a particular priority onto the console, a messaging framework, into a file, an email or via an ever-growing list of other strategies for it's transmission or storage.
At Core Developers Network we use log4j extensively, including as the primary logging mechanism for JBoss and Jetty. We can help you design and implement an effective logging and diagnostic strategy for your application based on log4j.
License: Apache Software License
Project site: http://jakarta.apache.org/log4j
log4j Download Page
Available from the log4j Documentation Page - We recommend Ceki's Complete log4j Manual.
Mailing List Archives:
log4j User
log4j Devel