A flexible layout configurable with pattern string. More...

#include <patternlayout.h>

Inheritance diagram for log4cxx::PatternLayout:

Public Member Functions
	PatternLayout ()
	Does nothing.

	PatternLayout (const LogString &pattern)
	Constructs a PatternLayout using the supplied conversion pattern.

	~PatternLayout ()

void	setConversionPattern (const LogString &conversionPattern)
	Use `conversionPattern` as to control formatting.

LogString	getConversionPattern () const
	Returns the value of the ConversionPattern option.

void	activateOptions (helpers::Pool &p) override
	Activate the options that were previously set with calls to option setters.

void	setOption (const LogString &option, const LogString &value) override
	Set `option` to `value`.

bool	ignoresThrowable () const override
	The PatternLayout does not handle the throwable contained within `LoggingEvents`.

void	format (LogString &output, const spi::LoggingEventPtr &event, helpers::Pool &pool) const override
	Produces a formatted string as specified by the conversion pattern.

Public Member Functions inherited from log4cxx::Layout
virtual	~Layout ()

virtual void	format (LogString &output, const spi::LoggingEventPtr &event, log4cxx::helpers::Pool &pool) const =0
	Implement this method to create your own layout format.

virtual LogString	getContentType () const
	Returns the content type output by this layout.

virtual void	appendHeader (LogString &output, log4cxx::helpers::Pool &p)
	Append the header for the layout format.

virtual void	appendFooter (LogString &output, log4cxx::helpers::Pool &p)
	Append the footer for the layout format.

virtual bool	ignoresThrowable () const =0
	If the layout handles the throwable object contained within `LoggingEvent`, then the layout should return `false`.

Public Member Functions inherited from log4cxx::spi::OptionHandler
virtual	~OptionHandler ()

virtual void	activateOptions (helpers::Pool &p)=0
	Activate the options that were previously set with calls to option setters.

virtual void	setOption (const LogString &option, const LogString &value)=0
	Set `option` to `value`.

Public Member Functions inherited from log4cxx::helpers::Object
virtual	~Object ()

virtual const helpers::Class &	getClass () const =0

virtual bool	instanceof (const Class &clazz) const =0

virtual const void *	cast (const Class &clazz) const =0

Protected Member Functions
virtual log4cxx::pattern::PatternMap	getFormatSpecifiers ()

Detailed Description

A flexible layout configurable with pattern string.

The goal of this class is to format a LoggingEvent and return the results as a string. The results depend on the conversion pattern.

The conversion pattern is closely related to the conversion pattern of the printf function in C. A conversion pattern is composed of literal text and format control expressions called conversion specifiers.

You are free to insert any literal text within the conversion pattern.

Each conversion specifier starts with a percent sign (%) and is followed by optional format modifiers and a conversion character. The conversion character specifies the type of data, e.g. logger, level, date, thread name. The format modifiers control such things as field width, padding, left and right justification. The following is a simple example.

Let the conversion pattern be "%-5p [%t]: %m%n" and assume that the log4cxx environment was set to use a PatternLayout. Then the statements

auto root = Logger::getRootLogger();
root->debug("Message 1");
root->warn("Message 2");

would yield the output

     DEBUG [main]: Message 1
     WARN  [main]: Message 2

Note that there is no explicit separator between text and conversion specifiers. The pattern parser knows when it has reached the end of a conversion specifier when it reads a conversion character. In the example above the conversion specifier %-5p means the level of the logging event should be left justified to a width of five characters.

The recognized conversion characters are:

Conversion Character	Effect
c	Used to output the name of the logger generating the logging event. The c conversion specifier can be optionally followed by precision specifier, that is a decimal constant in brackets. If a precision specifier is given, then only the corresponding number of right most components of the logger name will be printed. By default the logger name is printed in full. For example, for the logger name "a.b.c" the pattern c{2} will output "b.c".
C class	Used to output the class of the issuer of the logging event if the compiler used supports a macro to retrieve the method of the currently compiled line and if the LOG4CXX_TRACE-like macros are used to issue a logging request. In this case the macro LOG4CXX_* is expanded at compile time to generate location info of the logging event and adds the method name, besides file and line, if available. In most cases the provided method contains the classname and can therefore be retrieved form the location info as needed. Currently supported compilers are those from Microsoft, GNU-C and Borland.
d	Used to output the date of the logging event. The date conversion specifier may be followed by a set of braces containing a date and time pattern string compatible with java.text.SimpleDateFormat, ABSOLUTE, DATE or ISO8601. For example, d{HH:mm:ss,SSS}, d{dd MMM yyyy HH:mm:ss,SSS} or d{DATE}. If no date format specifier is given then ISO8601 format is assumed.
f	Used to output the short file name where the logging request was issued.
F	Used to output the file name where the logging request was issued.
l	Used to output location information of the caller which generated the logging event.
L	Used to output the line number from where the logging request was issued.
m	Used to output the application supplied message associated with the logging event. To output in a quoted context, add set of braces containing the quote character. Any quote character in the message is augmented with a second quote character. For example, use m{'} in an SQL insert statement.
M method	Used to output the method of the issuer of the logging event if the compiler used supports a macro to retrieve the method of the currently compiled line and if the LOG4CXX_TRACE-like macros are used to issue a logging request. In this case the macro LOG4CXX_* is expanded at compile time to generate location info of the logging event and adds the method name, besides file and line, if available. In most cases the provided method contains the classname which is ignored in every attempt to retrieve the method from the location info. Currently supported compilers are those from Microsoft, GNU-C and Borland.
n	Outputs the platform dependent line separator character or characters. This conversion character offers practically the same performance as using non-portable line separator strings such as "\n", or "\r\n". Thus, it is the preferred way of specifying a line separator.
p	Used to output the level of the logging event.
r	Used to output the number of milliseconds elapsed since the start of the application until the creation of the logging event.
t thread	Used to output the ID of the thread that generated the logging event.
T threadname	Used to output the name of the thread that generated the logging event. May not be available on all platforms.
x	Used to output the NDC (nested diagnostic context) associated with the thread that generated the logging event.
X	Used to output the MDC (mapped diagnostic context) associated with the thread that generated the logging event. All key/value pairs are output, each inside {} unless the X is followed by a key placed between braces, as in X{clientNumber} where `clientNumber` is the key. In this case the value in the MDC corresponding to the key will be output. See MDC class for more details.
J	Used to output JSON key/value pairs of all MDC (mapped diagnostic context) entries associated with the thread that generated the logging event. To output in a quoted context, add set of braces containing the quote character. Any quote character in the message is augmented with a second quote character. For example, use J{'} in an SQL insert statement. See MDC class for more details.
y	Used to wrap log with color. The y is the end of a color block.
Y	Used to wrap log with color. The Y is the start of a color block. Color will be taken from the log level. The default colors are: `TRACE` - blue `DEBUG` - cyan `INFO` - green `WARN` - yellow `ERROR` - red `FATAL` - magenta These colors are all customizable.
%	The sequence %% outputs a single percent sign.

By default the relevant information is output as is. However, with the aid of format modifiers it is possible to change the minimum field width, the maximum field width and justification.

The optional format modifier is placed between the percent sign and the conversion character.

The first optional format modifier is the left justification flag which is just the minus (-) character. Then comes the optional minimum field width modifier. This is a decimal constant that represents the minimum number of characters to output. If the data item requires fewer characters, it is padded on either the left or the right until the minimum width is reached. The default is to pad on the left (right justify) but you can specify right padding with the left justification flag. The padding character is space. If the data item is larger than the minimum field width, the field is expanded to accommodate the data. The value is never truncated.

This behavior can be changed using the maximum field width modifier which is designated by a period followed by a decimal constant. If the data item is longer than the maximum field, then the extra characters are removed from the beginning of the data item and not from the end. For example, it the maximum field width is eight and the data item is ten characters long, then the first two characters of the data item are dropped. This behavior deviates from the printf function in C where truncation is done from the end.

Below are various format modifier examples for the logger conversion specifier.

Format modifier	left justify	minimum width	maximum width	comment
%20c	false	20	none	Left pad with spaces if the logger name is less than 20 characters long.
%-20c	true	20	none	Right pad with spaces if the logger name is less than 20 characters long.
%.30c	NA	none	30	Truncate from the beginning if the logger name is longer than 30 characters.
%20.30c	false	20	30	Left pad with spaces if the logger name is shorter than 20 characters. However, if logger name is longer than 30 characters, then truncate from the beginning.
%-20.30c	true	20	30	Right pad with spaces if the logger name is shorter than 20 characters. However, if logger name is longer than 30 characters, then truncate from the beginning.

Below are some examples of conversion patterns.

%r [%t] %-5p %c %x - %m

This is essentially the TTCC layout.

%-6r [%15.15t] %-5p %30.30c %x - %m

Similar to the TTCC layout except that the relative time is right padded if less than 6 digits, thread name is right padded if less than 15 characters and truncated if longer and the logger name is left padded if shorter than 30 characters and truncated if longer.

The above text is largely inspired from Peter A. Darnell and Philip E. Margolis' highly recommended book "C -- a Software Engineering Approach", ISBN 0-387-97389-3.

Colorizing log output

In order to customize the colors for the Y specifier, options have been added to the PatternLayout in order to let users define their own colors. Foreground/background colors can be set, as well as other text effects. A user can also set the ANSI escape pattern directly if they want.

Each level can be set individually. The configuration options for the levels are as follows:

FatalColor
ErrorColor
WarnColor
InfoColor
DebugColor
ErrorColor

Foreground colors may be set by using fg(), background colors may be set by using bg(), and other options(such as bold) may be set as well.

Available colors:

Black
Red
Green
Yellow
Blue
Magenta
Cyan
White

Available graphics modes:

Bold
Dim
Italic
Underline
Blinking
Inverse
Strikethrough

Combining these together, we can configure our colors as we want, shown here in XML:

Set the background color to red, make text blinking and bold:

<param name="FatalColor" value="bg(red)|blinking|bold"/>

Set the foreground color to blue:

<param name="FatalColor" value="fg(blue)"/>

Set the foreground color to white and the background color to black:

<param name="FatalColor" value="fg(white)|bg(black)"/>

Clear the formatting for the specified level(no formatting will be applied):

<param name="FatalColor" value="none"/>

Set a color based off on an ANSI escape sequence(equivalent to setting fg(red)):

<param name="FatalColor" value="\x1b[31m"/>

Constructor & Destructor Documentation

◆ PatternLayout() [1/2]

log4cxx::PatternLayout::PatternLayout ( )

Does nothing.

◆ PatternLayout() [2/2]

log4cxx::PatternLayout::PatternLayout ( const LogString & pattern )

Constructs a PatternLayout using the supplied conversion pattern.

◆ ~PatternLayout()

log4cxx::PatternLayout::~PatternLayout ( )

Member Function Documentation

◆ activateOptions()

void log4cxx::PatternLayout::activateOptions ( helpers::Pool & p )

overridevirtual

Activate the options that were previously set with calls to option setters.

Calls createPatternParser

Implements log4cxx::spi::OptionHandler.

◆ format()

void log4cxx::PatternLayout::format	(	LogString &	output,
		const spi::LoggingEventPtr &	event,
		helpers::Pool &	pool
	)		const

overridevirtual

Produces a formatted string as specified by the conversion pattern.

Implements log4cxx::Layout.

◆ getConversionPattern()

LogString log4cxx::PatternLayout::getConversionPattern ( ) const

Returns the value of the ConversionPattern option.

◆ getFormatSpecifiers()

virtual log4cxx::pattern::PatternMap log4cxx::PatternLayout::getFormatSpecifiers ( )

protectedvirtual

◆ ignoresThrowable()

bool log4cxx::PatternLayout::ignoresThrowable ( ) const

inlineoverridevirtual

The PatternLayout does not handle the throwable contained within LoggingEvents.

Thus, it returns true.

Implements log4cxx::Layout.

◆ setConversionPattern()

void log4cxx::PatternLayout::setConversionPattern ( const LogString & conversionPattern )

Use conversionPattern as to control formatting.

The pattern can be a mix of literal content and conversion specifiers.

◆ setOption()

void log4cxx::PatternLayout::setOption	(	const LogString &	option,
		const LogString &	value
	)

overridevirtual

Set option to value.

Supported options	Supported values	Default value
ConversionPattern	{any}	%m%n
FatalColor	(1)	magenta
ErrorColor	(1)	red
WarnColor	(1)	yellow
InfoColor	(1)	green
DebugColor	(1)	cyan
TraceColor	(1)	blue

(1) The word None or valid ANSI escape sequence. A prefix of \x1b will be replaced with the ESC character. The character prefix ESC and suffix m will be added to the value if it does not begin with \x1b. Color names can be combined with graphic modes using a | separator. Enclose the color name in bg() to set the background. Enclose the color name in fg() to set the foreground.