log4j is a Java-based logging utility. It was originally written by Ceki G?lc? and is now a project of the Apache Software Foundation. It is used primarily as a debugging tool. log4j is one of several... More

log4j is a Java-based logging utility. It was originally written by Ceki G?lc? and is now a project of the Apache Software Foundation. It is used primarily as a debugging tool. log4j is one of several Java Logging Frameworks Log4j 1.2 offers six standard logging levels; from highest (coarsest) to lowest (finest): FATAL, ERROR, WARN, INFO, DEBUG, TRACE Also, custom logging levels can be added. There are 2 ways to configure log4j. One is with a properties file and the other is with an XML file. Within either you can define 3 main components: Loggers, Appenders and Layouts. Configuring logging via a file has the advantage of turning logging on or off without modifying the application that uses log4j. The application can be allowed to run with logging off until there's a problem, for example, and then logging can be turned back on simply by modifying the configuration file. Loggers are logical log file names. They are the names that are known to the Java application. Each logger is independently configurable as to what level of logging (FATAL, ERROR, etc) it currently logs. In early versions of log4j, these were called category and priority, but now they're called logger and level, respectively. The actual outputs are done by Appenders. There are numerous Appenders available, with descriptive names, such as FileAppender, ConsoleAppender, SocketAppender, SyslogAppender, NTEventLogAppender and even SMTPAppender. Multiple Appenders can be attached to any Logger, so it's possible to log the same information to a file locally and to a socket listener on another computer, for example. Appenders use Layouts to format log entries. A popular way to format one-line-at-a-time log files is PatternLayout, which uses a pattern string, much like the C (programming language) function printf. There are also HTMLLayout and XMLLayout formatters for use when HTML or XML formats are more convenient.   [edit]  Less