Log4j Format Specification
External
Internal
Overview
log4j calls its output format layout. Most commonly used is the pattern layout.
Pattern Layout
The pattern layout is defined by a conversion pattern string, where various element of a log event can be referred and the way they are intended to be displayed in a log file specified. The conversion pattern is closely related to the conversion pattern of the printf function in C. The conversion pattern is composed of:
Conversion Pattern
Literal Text
Literal text may include special characters (\t, \n \r \f). '\\' can be used to insert a backslash in the output.
Conversion Specifier
Each conversion specifier starts with a percent sign ('%') and it is followed by an optional format modifier and a mandatory conversion character.
Format Modifier
A format modifier modifies how the data generated by the pattern layout element
Conversion Character
The conversion character specifies the type of data (category, priority, date, thread name, etc)