Configuring log4j2 and log4j using a single log4j2

Question

I've migrated my application to log4j 2, and I've configured it via log4j2.xml

However, some of the libraries I'm using depend on log4j 1. If I run the application using:

-Dlog4j.configurationFile=path/to/log4j2.xml

log4j 1 complains about not finding a configuration file. I'm using the log4j 1.x bridge provided by log4j 2, log4j-1.2-api-2.0-rc1.jar. Is it possible to configure both using a single log4j2.xml?

An alternative I've tried is configuring both log4j and log4j2 together:

-Dlog4j.configurationFile=path/to/log4j2.xml -Dlog4j.configuration=path/to/log4j.xml

My concern is fragmentation of my logging configuration files and output. I'm also concerned about possible conflicts between log4j.xml and log4j2.xml. e.g. the logfile error.log is configured to use a FileAppender in log4j 1 and a RollingFileAppender in log4j 2.

Any advice?

[note]

This is the error I'm seeing:

log4j:WARN No appenders could be found for logger (org.apache.activemq.util.ThreadPoolUtils).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.

The version of log4j 2 I'm using is log4j 2.0 rc1.

[answer]

Seems like activemq-5.8.0.jar was bundled with log4j 1. The solution was simply to load the log4j 1.x bridge before activemq.

Answer 1

In a maven project using log4j2, it is possible to exclude log4j from modules that use it, in the pom, in order to enable log4j2 to take over:

<dependencies>
    <dependency>
        <groupId>commons-configuration</groupId>
        <artifactId>commons-configuration</artifactId>
        <version>1.4</version>
        <!--force usage of log4j2-->
        <exclusions>
            <exclusion>
                <groupId>log4j</groupId>
                <artifactId>log4j</artifactId>
            </exclusion>
        </exclusions>
    </dependency>
    <dependency>
        <groupId>org.apache.logging.log4j</groupId>
        <artifactId>log4j-api</artifactId>
        <version>2.3</version>
    </dependency>
    <dependency>
        <groupId>org.apache.logging.log4j</groupId>
        <artifactId>log4j-core</artifactId>
        <version>2.3</version>
    </dependency>
    <dependency>
        <groupId>org.apache.logging.log4j</groupId>
        <artifactId>log4j-1.2-api</artifactId>
        <version>2.3</version>
    </dependency>
    <dependency>
        <groupId>org.apache.logging.log4j</groupId>
        <artifactId>log4j-web</artifactId>
        <version>2.3</version>
    </dependency>
</dependencies>

More info about that in the log4j FAQ

Answer 2

I would recommend using the log4j-1.2 adapter that is included in the log4j2 distribution. That way, any libraries coded to the log4j-1.2 API will work with log4j2 without any code changes.

Your classpath should include:

• log4j-api-2.6.1.jar
• log4j-core-2.6.1.jar
• log4j-1.2-api-2.6.1.jar
• log4j2.xml

Your classpath should not include:

• log4j-1.2.x.jar
• log4j.properties or log4j.xml (these will be ignored by log4j2 anyway)

See also http://logging.apache.org/log4j/2.x/faq.html#which_jars