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

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)

Answer 2

I like to include all of the slf4j facades/re-routers/whateveryoucallthem. Also note the "provided" hack, which keeps dependencies from pulling in commons logging; previously I was using a fake empty commons logging library called version-99.0-does-not-exist.

Also see http://blog.springsource.com/2009/12/04/logging-dependencies-in-spring/

<dependencies>
    <dependency>
        <groupId>commons-logging</groupId>
        <artifactId>commons-logging</artifactId>

        <!-- use provided scope on real JCL instead -->
        <!-- <version>99.0-does-not-exist</version> -->

        <version>1.1.1</version>

        <scope>provided</scope>
    </dependency>

    <dependency>
        <groupId>commons-logging</groupId>
        <artifactId>commons-logging-api</artifactId>

        <!-- use provided scope on real JCL instead -->
        <!-- <version>99.0-does-not-exist</version> -->

        <version>1.1</version>

        <scope>provided</scope>
    </dependency>

    <!-- the slf4j commons-logging replacement -->
    <!-- if any package is using jakarta commons logging this will -->
    <!-- re-route it through slf4j. -->
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>jcl-over-slf4j</artifactId>

        <version>${version.slf4j}</version>
    </dependency>

    <!-- the slf4j log4j replacement. -->
    <!-- if any package is using log4j this will re-route -->
    <!-- it through slf4j. -->
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>log4j-over-slf4j</artifactId>

        <version>${version.slf4j}</version>
    </dependency>

    <!-- the slf4j java.util.logging replacement. -->
    <!-- if any package is using java.util.logging this will re-route -->
    <!-- it through slf4j. -->
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>jul-to-slf4j</artifactId>
        <version>${version.slf4j}</version>
    </dependency>

    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>

        <version>${version.slf4j}</version>
    </dependency>

    <dependency>
        <groupId>ch.qos.logback</groupId>
        <artifactId>logback-classic</artifactId>

        <version>${version.logback}</version>
    </dependency>
</dependencies>

<properties>
    <version.logback>0.9.15</version.logback>
    <version.slf4j>1.5.8</version.slf4j>
</properties>

Answer 3

have you looked at log4j.NDC and MDC? This at least allows you to tag thread specific data to your logging. Not exactly what you're asking, but might be useful. There's a discussion here.