Optional Appender Layouts

[Mark R Durman/CA/US/MQSolutions <md...@mqsolutions.com>]

I have an Appender that can produce serialized logging events or formatted 
logging events. I wanted to support an optional Layout to determine which 
output to produce. If a Layout was supplied it would be called to format 
the event, otherwise the log event would be serialized. 

However, support for optional layouts seems rather counter intuitive. That 
is, if an Appender returns false to requiresLayout() a Layout is never 
passed to the Appender even if one if supplied. On the other hand, if I 
return true from requiresLayout and the user omits the layout, log4j spits 
out an error. That's confusing for end users and requires documentation to 
cover the behaviour.

Returning false from requiresLayout() implies that the Appender does not 
require a layout, not that it doesn't ever use one. I believe it would be 
more logical for log4j configuration to set an Appender's layout if one is 
specified, regardless of the response from requiresLayout(). That way, an 
Appender that doesn't use a Layout won't call it, an Appender that uses an 
optional Layout can test for it's existence, and an Appender that requires 
a Layout will continue to function as before.

This kind of operation would also apply to other Appenders (like the 
JMSAppender). That has the capability of handling serialized log events 
and formatted textual events (in XML, for example).

Regards

Mark Durman
MQ Solutions LLC