This article describes what a log formatter is.
Handlers may be configured with a formatter, which knows how to format log records. The event (represented by the log record object) is passed to the appropriate formatter by the handler. The formatter returns formatted output to the handler, which then writes it to the output device.
The formatter is responsible for rendering the event for output. This usually means the formatter uses the ResourceBundle specified in the event to look up the message in the appropriate language.
Formatters are attached to handlers using the setFormatter method.
You can find the java.util.logging documentation at http://java.sun.com/j2se/.
Related concepts
Loggers
Log handlers
Log levels
Log filters