Log4j 1.2 Bridge

The Log4j 1.2 Bridge allows applications coded to use Log4j 1.2 API to use Log4j 2 instead.


The Log4j 1.2 bridge is dependent on the Log4j 2 API. The following Log4j 1.x methods will behave differently when the Log4j 2 Core module is included then when it is not:

Method Without log4j-core With log4j-core
Category.getParent() Returns null Returns parent logger
Category.setLevel() NoOp Sets Logger Level
Category.setPriority() NoOp Sets Logger Level
Category.getAdditivity() Returns false Returns Logger's additivity setting
Category.setAdditivity() NoOp Sets additivity of LoggerConfig
Category.getResourceBundle() NoOp Returns the resource bundle associated with the Logger
BasicConfigurator.configure() NoOp Reconfigures Log4j 2

If log4j-core is not present location information will not be accurate in calls using the Log4j 1.2 API. The config package which attempts to convert Log4j 1.x configurations to Log4j 2 is not supported without Log4j 2.

For more information, see Runtime Dependencies.


To use the Log4j Legacy Bridge, you must first identify and remove all the Log4j 1.x JARs from the application and replace them with the bridge JAR. Once in place, all logging that uses Log4j 1.x will be routed to Log4j 2.

If you are using Maven, you can easily identify any Log4j 1.x dependencies in your project by running the following command in your terminal:

mvn dependency:tree | grep 'log4j:log4j:'

This command will generate a dependency tree for your project and filter the results to show only Log4j 1.x dependencies. If you find any, you will need to update your pom.xml file to remove Log4j1 or exclude them otherwise.

While we have improved the compatibility of the bridge in the past, applications that try to modify legacy Log4j by adding Appenders, Filters, etc, may experience problems. In this case, migrating those components to Log4j 2 first is recommended.