Hello Joern, At an earlier time, certain classes expected the Appender interface to have a setter/getter for the layout property. AbstractLayoutAction is one such class. However, it is no longer used. (I just removed it.) Many logback appenders do not require a layout and can have their layout property set to null. Having a layout property in Appender and AppenderBase is just noise for such appenders but otherwise not harmful. They have a property, i.e. layout, which they don't use... If the Appender interface did not contain the layout property, we would probably have two distinct appender base implementations, AppenderBase and AppenderBaseWithLayout (possibly with an additional interface such as AppenderWithLayout). Come to think of it, we would also need to handle the UnsyncronizedAppenderBase branch of the class hierarchy. Adding UnsyncronizedAppenderBaseWithLayout would be too unwieldy. :-) For developers coming from log4j, AppenderBase having the same implementation for setLayout and getLayout as log4j's AppenderSkeleton class would help them migrate to logback with a little bit more ease, at least with less surprise. I wonder what I was thinking when I implemented layout setter and getters in LayoutBase as nop. Joern Huxhorn wrote:
Hi Ceki,
the only thing that I don't understand is why Appender requires a layout at all. It would by cleaner if there was a sub-interface, e.g. LayoutAwareAooender (just a spontaneous suggestion), that extended Appender and would add said methods. Some appenders, like SocketAppender or some fictitious appender that would simply serialize the events to a file (I'm planning to implement such an appender, btw), just don't need a layout at all. AppenderBase would then just implement the basic Appender interface, leaving the layout implementation to appenders that would really require it.
This topic is covered by both http://jira.qos.ch/browse/LBCORE-1 and http://jira.qos.ch/browse/LBCORE-56
Regards, Joern.
-- Ceki Gülcü Logback: The reliable, generic, fast and flexible logging framework for Java. http://logback.qos.ch