How to use commons-logging api with the latest version of log4j 2

Question

I want to use commons-logging API with log4j 2.

My classes have the following code get the logger ( the commons-logging api )

package com.example.testwebapp;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;


public class Log4j2ConfigBuilder {
  
  public static void main(String[] args) { 
    getLog().debug("DEBUG log entryc 11111 ");
    getLog().info("INFO log entry ");
    getLog().error("ERROR log entry ");
    getLog().warn("#############  WAR log entry ");
  }

  /**
   * @return The logger for the class.
   */
  private static Log getLog() {
    return LogFactory.getLog(Log4j2ConfigBuilder.class);
  }
}

I am facing problem, similar to what described in the following question : I'm getting "NoClassDefFoundError: org/apache/logging/log4j/util/ReflectionUtil"

So the short question what is the maven dependencies I have to use, to get the commons-logging api work with latest version of log4j2

Following is my non-working pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>TestWebApp</artifactId>
    <version>1.0-SNAPSHOT</version>
    <name>TestWebApp</name>
    <packaging>war</packaging>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.target>1.8</maven.compiler.target>
        <maven.compiler.source>1.8</maven.compiler.source>
        <junit.version>5.7.1</junit.version>
        <log4j.version>2.17.0</log4j.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.0.1</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>${junit.version}</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-engine</artifactId>
            <version>${junit.version}</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>commons-logging</groupId>
            <artifactId>commons-logging</artifactId>
            <version>1.2</version>
        </dependency>

        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-api</artifactId>
            <version>${log4j.version}</version>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>${log4j.version}</version>
        </dependency>
        <dependency>
            <groupId>commons-logging</groupId>
            <artifactId>commons-logging</artifactId>
            <version>1.2</version>
            <scope>compile</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>3.3.1</version>
            </plugin>
        </plugins>
    </build>
</project>

Answer 1

The vanilla Commons Logging has a fixed list of logging implementations it can discover (cf. documentation). Log4j 1.x is among them, but Log4j 2.x is not.

Therefore you need to add the Log4j Commons Logging Adapter to your classpath:

<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-jcl</artifactId>
    <version>${log4j.version}</version>
</dependency>

Under the hood this contains an alternative implementation of LogFactory, which will be automatically discovered and used through the ServiceLoader mechanism.