Java logging framework

A Java logging framework is a computer data logging package for the Java platform. This article covers general purpose logging frameworks.

Logging refers to the recording of activity by an application and is a common issue for development teams. Logging frameworks ease and standardize the process of logging for the Java platform. In particular they provide flexibility by avoiding explicit output to the console (see Appender below). Where logs are written becomes independent of the code and can be customized at runtime.

Unfortunately the JDK did not include logging in its original release so by the time the Java Logging API was added several other logging frameworks had become widely used – in particular Apache Commons Logging (also known as Java Commons Logging or JCL) and Log4j. This led to problems when integrating different third-party libraries (JARs) each using different logging frameworks. Pluggable logging frameworks (wrappers) were developed to solve this problem.

Logging is typically broken into three major pieces: the Logger, the Formatter and the Appender (or Handler).

Simpler logging frameworks, like |Java Logging Framework by the Object Guy, combine the logger and the appender. This simplifies default operation, but it is less configurable, especially if the project is moved across environments.

A Logger is an object that allows the application to log without regard to where the output is sent/stored. The application logs a message by passing an object or an object and an exception with an optional severity level to the logger object under a given name/identifier.

A logger has a name. The name is usually structured hierarchically, with periods (.) separating the levels. A common scheme is to use the name of the class or package that is doing the logging. Both Log4j and the Java logging API support defining handlers higher up the hierarchy.

For example, the logger might be named "com.sun.some.UsefulClass". The handler can be defined for any of the following: