[logback-dev] Layout setter/getter methods in AppenderBase

Joern Huxhorn jhuxhorn at googlemail.com
Tue Feb 10 01:01:53 CET 2009

On 09.02.2009, at 23:15, Ceki Gulcu wrote:

> 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.)

Oh, I see, "for historic reasons" :)

> 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...

Well, yes, you are right. It's not downright harmful... but it is  
somewhat confusing for users (not developers) of the appenders and  
makes them wonder what the layout is about. People actually asked me  
about that...

> 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. :-)

I don't think that this would be necessary because it would be enough  
if the mentioned classes would simply implement Appender (without the  
layout methods) and appenders requiring the layout would additionally  
implement the extended interface, in just the way that is necessary  
for their desired behavior (e.g. even synchronized/locked if required,  
which isn't the case right now).

This is more or less an aesthetic reasoning and I wouldn't consider it  
very important.

Concerning your original question: the new implementation is  
definitely better than before!

> 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.

I know this feeling all too well...
But this is actually a good thing because it's a sign that we keep  
developing our skills ;)


> 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
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