Log4cxx custom appender

Question

Is it possible to write a custom appender for log4cxx and have it configurable via a properties file (like the built-in appenders)? I'd prefer doing this without having to rebuild log4cxx (e.g. by deriving/extending an existing appender), if possible.

Can you point me toward an example?

Answer 1

You can inherit from AppenderSkeleton or WriterAppender and get the same underlying behaviors without having to rebuilt log4cxx.

http://svn.apache.org/viewvc/incubator/log4cxx/trunk/src/test/cpp/vectorappender.h?view=markup http://svn.apache.org/viewvc/incubator/log4cxx/trunk/src/test/cpp/vectorappender.cpp?view=markup

Answer 2

brlcad's suggestion is correct - at my company we've used this method for our own custom appenders.

You can in fact already configure these from a configuration file - the macros like DECLARE_LOG4CXX_OBJECT(CustomAppenderClassName) in the class definition set up the log4cxx environment. You can refer to your appender type by your "CustomAppenderClassName". A configfile (old-style) showing a standard and custom appender, using the standard layouts for the custom appender:

# Set "realtime" logger level to DEBUG and create two appenders - one to be
# a standard rolling file appender, the other custom.
log4j.logger.realtime=ERROR, StandardAppender, CustomAppender

# StandardAppenderis set to be a RollingFileAppender
log4j.appender.StandardAppender=org.apache.log4j.RollingFileAppender
log4j.appender.StandardAppender.File=example.log

log4j.appender.StandardAppender.MaxFileSize=100KB
# Keep one backup file
log4j.appender.StandardAppender.MaxBackupIndex=1

# StandardAppender uses PatternLayout.
log4j.appender.StandardAppender.layout=org.apache.log4j.PatternLayout
log4j.appender.StandardAppender.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n

# CustomAppender uses PatternLayout too
log4j.appender.CustomAppender=CustomAppenderClassName
log4j.appender.CustomAppender.layout=org.apache.log4j.PatternLayout
log4j.appender.CustomAppender.layout.ConversionPattern=%m