How can I configure logback conditionally based on context name? - logback

Question

I have three separate projects, each with their own embedded logback.xml files. Each of these files includes a common logging config file in the user's home durectory:
<include file="${user_home}/loggingConfig.xml"/>
After the include, I have this specification:
<root level="error">
<appender-ref ref="${appender:-console}" />
</root>
This allows the user to configure their log levels and appenders, and have them applied by the core logging config file.
For example, in ~/loggingConfig.xml I have this line:
<property name="appender" value="file" />
But co-workers who prefer console logging leave that line out.
The problem is I would like to use different appenders for each log file. In otherwords, I would like to conditionally set a different appender based on which project is reading the customized config file.
I realize I could configure each project to read differently named config files, but I would like to eliminate the clutter and allow for shared configuration as well.

Answer 1

The documentation is a bit spare for advanced configuration, but I found that you can use the logback context name as a variable with conditional logging. So for each project I define a custom context name in the projects logback.xml file:
<contextName>project1</contextName>
etc...
Then in my ~/loggingConfig.xml file I can do this:
<property name="appender" value="file" />
<!--if condition='property("CONTEXT_NAME").equalsIgnoreCase("project1")'>
<then>
<property name="appender" value="file" />
</then>
</if-->
<if condition='property("CONTEXT_NAME").equalsIgnoreCase("project2")'>
<then>
<property name="appender" value="console" />
</then>
</if>
<if condition='property("CONTEXT_NAME").equalsIgnoreCase("project3")'>
<then>
<property name="appender" value="file" />
</then>
</if>
This can get a bit clunky, but in reality I am using this solution to configure properties used by a single appender for different projects, while still having a graceful fallback to a default value for projects that don't have their own conditional block.

Answer 2

In case this helps anyone else, this is how I set up conditional logback configuration with a property that can contain multiple appenders:
<root level="${logback.loglevel}">
<if condition='isDefined("logback.appenders")'>
<then>
<if condition='property("logback.appenders").contains("CONSOLE")'>
<then>
<appender-ref ref="CONSOLE"/>
</then>
</if>
<if condition='property("logback.appenders").contains("FILE")'>
<then>
<appender-ref ref="FILE"/>
</then>
</if>
<if condition='property("logback.appenders").contains("GELF")'>
<then>
<appender-ref ref="GELF"/>
</then>
</if>
</then>
<else>
<appender-ref ref="CONSOLE"/>
</else>
</if>
</root>