What are the main features of Apache Log4j?

Log4j is a logging library for Java applications developed by Apache Software Foundation. Here are the main features for Log4j:

log4j is optimized for speed.

log4j is based on a named logger hierarchy.

log4j is fail-stop. However, altough it certainly strives to ensure delivery, log4j does not guarantee that each log statement will be delivered to its destination.

log4j is thread-safe.

log4j is not restricted to a predefined set of facilities.

Logging behavior can be set at runtime using a configuration file. Configuration files can be property files or in XML format.

log4j is designed to handle Java Exceptions from the start.

log4j can direct its output to a file, the console, an java.io.OutputStream, java.io.Writer, a remote server using TCP, a remote Unix Syslog daemon, to a remote listener using JMS, to the NT EventLog or even send e-mail.

log4j uses 6 levels, namely TRACE, DEBUG, INFO, WARN, ERROR and FATAL.

The format of the log output can be easily changed by extending the Layout class.

The target of the log output as well as the writing strategy can be altered by implementations of the Appender interface.

log4j supports multiple output appenders per logger.

log4j supports internationalization.

⇒ Main Modules in Apache Log4j

⇐ What Is Apache Log4j - A Logging Library for Java

⇑ Introduction to Apache Log4j

⇑⇑ FAQ for Apache Log4j