Logging library for java

 log4j is a tool to help the programmer output log statements to a variety of
 output targets.
 .
 It is possible to enable logging at runtime without modifying the application
 binary. The log4j package is designed so that log statements can remain in
 shipped code without incurring a high performance cost.
 .
 One of the distinctive features of log4j is the notion of hierarchical
 loggers. Using loggers it is possible to selectively control which log
 statements are output at arbitrary granularity.
 .
 Log4j can output to: a file, a rolling file, a database with a JDBC driver,
 many output asynchronously, a JMS Topic, a swing based logging console,
 the NT event log, /dev/null, a SMTP server (using javamail), a socket server,
 syslog, telnet daemon and stdout.
 .
 The format of the output can be defined using one of the various layout
 (or user defined layout) like: simple text, html, date, pattern defined and
 XML.