Log4J - SiftingAppender-like functionality

Question

I work in a project that uses Log4J. One of the requirement is to create a separate log file for each thread; this itself was a odd issue, somewhat sorted by creating a new FileAppender on the fly and attaching it to the Logger instance.

Logger logger = Logger.getLogger(<thread dependent string>);
FileAppender appender = new FileAppender();
appender.setFile(fileName);
appender.setLayout(new PatternLayout(lp.getPattern()));
appender.setName(<thread dependent string>);
appender.setThreshold(Level.DEBUG);
appender.activateOptions();
logger.addAppender(appender);

Everything went fine until we realised that another library we use - Spring Framework v3.0.0 (which use Commons Logging) - does not play ball with the technique above – the Spring logging data is “seen” only by Appenders initialised from the log4.configuration file but not by the runtime created Appenders. So, back to square one.

After some investigation, I found out that the new and improved LogBack has an appender - SiftingAppender – which does exactly what we need i.e. thread level logging on independent files.

At the moment, moving to LogBack is not an option, so, being stuck with Log4J, how can I achieve SiftingAppender-like functionality and keep Spring happy as well ?

Note: Spring is only used for JdbcTemplate functionality, no IOC; in order to “hook” Spring’s Commons Logging to Log4J I added this line in the log4j.properties file:

log4j.logger.org.springframework=DEBUG

as instructed here.

Answer 1

In Log4j2, we can now use RoutingAppender:

The RoutingAppender evaluates LogEvents and then routes them to a subordinate Appender. The target Appender may be an appender previously configured and may be referenced by its name or the Appender can be dynamically created as needed.

From their FAQ:

How do I dynamically write to separate log files? Look at the RoutingAppender. You can define multiple routes in the configuration, and put values in the ThreadContext map that determine which log file subsequent events in this thread get logged to.

Answer 2

LogBack is accessed via the slf4j api. There is an adapter library called jcl-over-sjf4j which exposes the commons logging interface but makes all the logging to the slf4j API, which goes directly to the implementation - LogBack. If you are using maven, here are the dependencies:

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.5.8</version>
</dependency>
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>jcl-over-slf4j</artifactId>
    <version>1.5.8</version>
</dependency> 
<dependency>
    <groupId>ch.qos.logback</groupId>
    <artifactId>logback-core</artifactId>
    <version>0.9.18</version>
</dependency>

(and add the commons-logging to the exclusion list, see here)