Convert Java Project from Log4j 1 to Log4j2

Many times while working on old Java projects we find Log4j 1.x is used. But as the Log4j2 is the new one; hence to upgrade to Log4j2 we need to change the all the files with new package details.

This is a tedious job. OpenRewrite comes up with a solution; where you can do the below steps to convert your project to Log4j 2 from Log4j 1.x

Steps:

• Navigate to the project folder in command prompt
• Run the below command

mvn -U org.openrewrite.maven:rewrite-maven-plugin:run -Drewrite.recipeArtifactCoordinates=org.openrewrite.recipe:rewrite-logging-frameworks:RELEASE -Drewrite.activeRecipes=org.openrewrite.java.logging.log4j.Log4j1ToLog4j2

• This will convert all the imports in file to Log42 packages & remove Log4j 1.x dependency & will add the Log4j2 dependencies automatically in pom.xml
• Add the LMAX Disruptor dependency in pom.xml as below

<dependency>

<groupId>com.lmax</groupId>

<artifactId>disruptor</artifactId>

<version>3.4.4</version>

</dependency>

• Create the log4j2.xml (under src\main\resources folder); a sample one could be like below. Here the assumption is log files are created within logs folder of Tomcat . Replace <AppName> with the app name.

<?xml version="1.0" encoding="UTF-8"?>

<Configuration status="WARN">

<Appenders>

<Console name="Console" target="SYSTEM_OUT">

<PatternLayout pattern="%d{dd-MM-yyyy HH:mm:ss} [%t] %-5p %c - %m%n"/>

</Console>

<!-- Generate rolling log for router with per hour interval policy -->

<RollingFile name="ProcessorRollingFile" fileName="${sys:catalina.home}/logs/<AppName>.log" filePattern="${sys:catalina.home}/logs/$${date:yyyy-MM-dd}/<AppName>-%d{yyyy-MM-dd-HH}-%i.log.gz">

<PatternLayout>

<!--<pattern>%d{ISO8601} [%t] %p %c %L - %m%n</pattern>-->

<pattern>%d{dd-MM-yyyy HH:mm:ss} [%t] %-5p %c - %m%n</pattern>

</PatternLayout>

<Policies>

<SizeBasedTriggeringPolicy size="500 MB"/>

</Policies>

<DefaultRolloverStrategy max="100"/>

</RollingFile>

<!-- Register Async appender -->

<Async name="AsyncRollingFile">

<AppenderRef ref="ProcessorRollingFile"/>

</Async>

</Appenders>

<Loggers>

<AsyncLogger name="root" level="WARN" additivity="false">

<AppenderRef ref="AsyncRollingFile"/>

</AsyncLogger>

</Loggers>

</Configuration>

In case you do skip tests in the project while running maven then the same needs to be applied while executing the maven command for OpenRewrite. If you use a profile, the same needs to be added to in maven command. If the profile name is Live the full command with skip tests will look like below:

mvn -U org.openrewrite.maven:rewrite-maven-plugin:run -Drewrite.recipeArtifactCoordinates=org.openrewrite.recipe:rewrite-logging-frameworks:RELEASE -Drewrite.activeRecipes=org.openrewrite.java.logging.log4j.Log4j1ToLog4j2 -Dmaven.test.skip=true -PLive

Further Reading: https://docs.openrewrite.org/recipes/java/logging/log4j/log4j1tolog4j2