Log4j Pattern Layout
External
Internal
Overview
The pattern layout is defined by a conversion pattern string.
Conversion Pattern
A conversion pattern string , where various elements 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:
There is no explicit separator between literal text and conversion specifiers. The pattern parser knows when it has reached the end of a conversion specifier when it reads a conversion character.
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:
%-5c
Format Modifier
A format modifier modifies how the data generated by the conversion specifier is displayed: field with, padding and justification.
Conversion Character
The conversion character specifies the type of data:
- 'c': category (or logger).
c{precision}
- 'd': date.
- 'm': application supplied message associated with this log event.
- 'n': platform dependent line separator.
- 'p': the level of the logging event
- 't': thread name
Throwable Handling
If the pattern string does not contain a specifier to handle a Throwable being logged, parsing of the pattern will act as if the "%xEx" specifier had been added to the end of the string. To suppress formatting of the Throwable completely, simply add "%ex{0}" as a specifier in the pattern string.