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PatternLayout Class Reference

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

Inheritance diagram for PatternLayout:
Layout OptionHandler ObjectImpl Object Object

Public Member Functions

 PatternLayout ()
 Does nothing. More...
 
 PatternLayout (const LogString &pattern)
 Constructs a PatternLayout using the supplied conversion pattern. More...
 
void setConversionPattern (const LogString &conversionPattern)
 Set the ConversionPattern option. More...
 
LogString getConversionPattern () const
 Returns the value of the ConversionPattern option. More...
 
virtual void activateOptions (log4cxx::helpers::Pool &p)
 Call createPatternParser. More...
 
virtual void setOption (const LogString &option, const LogString &value)
 Set option to value. More...
 
virtual bool ignoresThrowable () const
 The PatternLayout does not handle the throwable contained within LoggingEvents. More...
 
virtual void format (LogString &output, const spi::LoggingEventPtr &event, log4cxx::helpers::Pool &pool) const
 Produces a formatted string as specified by the conversion pattern. More...
 
- Public Member Functions inherited from Layout
virtual ~Layout ()
 
void addRef () const
 
void releaseRef () const
 
virtual LogString getContentType () const
 Returns the content type output by this layout. More...
 
virtual void appendHeader (LogString &output, log4cxx::helpers::Pool &p)
 Append the header for the layout format. More...
 
virtual void appendFooter (LogString &output, log4cxx::helpers::Pool &p)
 Append the footer for the layout format. More...
 
- Public Member Functions inherited from OptionHandler
virtual ~OptionHandler ()
 
- Public Member Functions inherited from Object
virtual const helpers::ClassgetClass () const
 
virtual ~Object ()
 
virtual bool instanceof (const Class &clazz) const =0
 
virtual const void * cast (const Class &clazz) const =0
 
- Public Member Functions inherited from ObjectImpl
 ObjectImpl ()
 
virtual ~ObjectImpl ()
 

Protected Member Functions

virtual
log4cxx::pattern::PatternMap 
getFormatSpecifiers ()
 

Additional Inherited Members

- Static Public Member Functions inherited from Object
static const helpers::ClassgetStaticClass ()
 
static const
log4cxx::helpers::ClassRegistration
registerClass ()
 
- Protected Attributes inherited from ObjectImpl
unsigned int volatile ref
 

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

     LoggerPtr root = Logger::getRoot();
     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 logger of the logging event. The logger 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".

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.
 <tr>
 <td align=center><b>F</b></td>

 <td>Used to output the file name where the logging request was
 issued.

 </tr>

 <tr>
 <td align=center><b>l</b></td>

 <td>Used to output location information of the caller which generated
 the logging event.

 </td>
 </tr>

 <tr>
 <td align=center><b>L</b></td>

 <td>Used to output the line number from where the logging request
 was issued.
 </tr>


 <tr>
 <td align=center><b>m</b></td>
 <td>Used to output the application supplied message associated with
 the logging event.</td>
 </tr>

 <tr>
 <td align=center><b>n</b></td>

 <td>Outputs the platform dependent line separator character or
 characters.

 <p>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.


 </tr>

 <tr>
 <td align=center><b>p</b></td>
 <td>Used to output the level of the logging event.</td>
 </tr>

 <tr>

 <td align=center><b>r</b></td>

 <td>Used to output the number of milliseconds elapsed since the start
 of the application until the creation of the logging event.</td>
 </tr>


 <tr>
 <td align=center><b>t</b></td>

 <td>Used to output the name of the thread that generated the
 logging event.</td>

 </tr>

 <tr>

 <td align=center><b>x</b></td>

 <td>Used to output the NDC (nested diagnostic context) associated
 with the thread that generated the logging event.
 </td>
 </tr>


 <tr>
 <td align=center><b>X</b></td>

 <td>

 <p>Used to output the MDC (mapped diagnostic context) associated
 with the thread that generated the logging event. The <b>X</b>
 conversion character <em>must</em> be followed by the key for the
 map placed between braces, as in <b>\%X{clientNumber}</b> where
 <code>clientNumber</code> is the key. The value in the MDC
 corresponding to the key will be output.</p>

 <p>See MDC class for more details.
 </p>

 </td>
 </tr>

 <tr>

 <td align=center><b>\%</b></td>

 <td>The sequence \%\% outputs a single percent sign.
 </td>
 </tr>

 </table>

 <p>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.

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

 <p>The first optional format modifier is the <em>left justification
 flag</em> which is just the minus (-) character. Then comes the
 optional <em>minimum field width</em> 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.

 <p>This behavior can be changed using the <em>maximum field
 width</em> 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
 <em>beginning</em> 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.

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

 <p>
 <TABLE BORDER=1 CELLPADDING=8>
 <tr>
 <td align=center><b>Format modifier</b></td>
 <td align=center><b>left justify</b></td>
 <td align=center><b>minimum width</b></td>
 <td align=center><b>maximum width</b></td>
 <td align=center><b>comment</b></td>
 </tr>

 <tr>
 <td align=center>\%20c</td>
 <td align=center>false</td>
 <td align=center>20</td>
 <td align=center>none</td>

 <td>Left pad with spaces if the logger name is less than 20
 characters long.

 <tr> <td align=center>\%-20c</td> <td align=center>true</td> <td
 align=center>20</td> <td align=center>none</td> <td>Right pad with
 spaces if the logger name is less than 20 characters long.

 <tr>
 <td align=center>\%.30c</td>
 <td align=center>NA</td>
 <td align=center>none</td>
 <td align=center>30</td>

 <td>Truncate from the beginning if the logger name is longer than 30
 characters.

 <tr>
 <td align=center>\%20.30c</td>
 <td align=center>false</td>
 <td align=center>20</td>
 <td align=center>30</td>

 <td>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.

 <tr>
 <td align=center>\%-20.30c</td>
 <td align=center>true</td>
 <td align=center>20</td>
 <td align=center>30</td>

 <td>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.

 </table>

 <p>Below are some examples of conversion patterns.

 <p><b>\%r [\%t] \%-5p \%c \%x - \%m\n</b>
 <p>This is essentially the TTCC layout.

 <p><b>\%-6r [\%15.15t] \%-5p \%30.30c \%x - \%m\n</b>

 <p>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.

 <p>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.

Constructor & Destructor Documentation

Does nothing.

PatternLayout ( const LogString pattern)

Constructs a PatternLayout using the supplied conversion pattern.

Member Function Documentation

virtual void activateOptions ( log4cxx::helpers::Pool p)
virtual

Call createPatternParser.

Implements OptionHandler.

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

Produces a formatted string as specified by the conversion pattern.

Implements Layout.

LogString getConversionPattern ( ) const
inline

Returns the value of the ConversionPattern option.

virtual log4cxx::pattern::PatternMap getFormatSpecifiers ( )
protectedvirtual
virtual bool ignoresThrowable ( ) const
inlinevirtual

The PatternLayout does not handle the throwable contained within LoggingEvents.

Thus, it returns true.

Implements Layout.

void setConversionPattern ( const LogString conversionPattern)

Set the ConversionPattern option.

This is the string which controls formatting and consists of a mix of literal content and conversion specifiers.

virtual void setOption ( const LogString option,
const LogString value 
)
virtual

Set option to value.

The handling of each option depends on the OptionHandler instance. Some options may become active immediately whereas other may be activated only when activateOptions is called.

Implements OptionHandler.


The documentation for this class was generated from the following file: