In a recent post log4j-user list a developer asked whether it was possible for log4j to log differently depending on technical partitions such as web-app as opposed to EJB. The original discussion can be found at: http://marc.theaimsgroup.com/?t=116179536800005&r=1&w=2 A kind soul, namely James Stauffer, suggested filtering based on MDC. Here is an example of how you would do it in logback. ------------------------------------------ package chapter5; import org.slf4j.LoggerFactory; import ch.qos.logback.classic.Logger; import ch.qos.logback.classic.LoggerContext; import ch.qos.logback.classic.MDC; import ch.qos.logback.classic.joran.JoranConfigurator; import ch.qos.logback.core.joran.spi.JoranException; import ch.qos.logback.core.util.StatusPrinter; public class GoMDC { public static void main(String[] args) { Logger logger = (Logger) LoggerFactory .getLogger(GoMDC.class); LoggerContext lc = (LoggerContext) LoggerFactory.getILoggerFactory(); try { JoranConfigurator configurator = new JoranConfigurator(); configurator.setContext(lc); configurator.doConfigure("mdcFilter.xml"); } catch (JoranException je) { StatusPrinter.print(lc); } logger.debug("I know me " + 0); MDC.put("key", "val"); logger.debug("I know me " + 1); StatusPrinter.print(lc); } ------------------------------------------ Here the associated config file, "mdcFilter.xml". <configuration> <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender"> <layout class="ch.qos.logback.classic.PatternLayout"> <param name="Pattern" value="%-4relative [%thread] %-5level %X{testKey} - %msg%n" /> </layout> <filter class="ch.qos.logback.core.filter.EvaluatorFilter"> <Name>myFilter</Name> <OnMatch>DENY</OnMatch> <Evaluator class="ch.qos.logback.classic.boolex.JaninoEventEvaluator"> <Name>mdcEvaluator</Name> <Expression>mdc!=null && "val".equals(mdc.get("key"))</Expression> </Evaluator> </filter> </appender> <root> <level value="debug" /> <appender-ref ref="STDOUT" /> </root> </configuration> The above has been tested on logback version 0.5. It will yield the following output. 0 [main] DEBUG - I know me 0 |-INFO in ch.qos.logback.classic.joran.action.ConfigurationAction - Ignoring debug attribute. |-INFO in ch.qos.logback.core.joran.action.AppenderAction - About to instantiate appender of type [ch.qos.logback.core.ConsoleAppender] |-INFO in ch.qos.logback.core.joran.action.AppenderAction - Naming appender as [STDOUT] |-INFO in ch.qos.logback.core.joran.action.NestedComponentIA - is dmmed applicable for /configuration/appender/filter |-INFO in ch.qos.logback.core.joran.action.NestedComponentIA - Pushing component <filter> on top of the object stack. |-INFO in ch.qos.logback.core.joran.action.NestedComponentIA - is dmmed applicable for /configuration/appender/filter/Evaluator |-INFO in ch.qos.logback.core.joran.action.NestedComponentIA - Pushing component <Evaluator> on top of the object stack. |-INFO in ch.qos.logback.core.joran.action.AppenderAction - Popping appender named [STDOUT] from the object stack |-INFO in ch.qos.logback.classic.joran.action.LevelAction - root level set to DEBUG |-INFO in ch.qos.logback.core.joran.action.AppenderRefAction - Attaching appender named [STDOUT to Logger[root] Note that the last log statement is suppressed, which is the whole point of the exercise. -- Ceki Gülcü Logback: The reliable, generic, fast and flexible logging framework for Java. http://logback.qos.ch