Log4j 2 provides support for the Log4j 1 logging methods by providing alternate implementations of the classes containing those methods. These classes may be found in the log4j-1.2-api jar distributed with the project. All calls to perform logging will result in the data passed to the logging methods to be forwarded to the Log4j2 API where they can be processed by implementations of the Log4j 2 API.
Log4j 2 provides experimental support for Log4j 1 configuration files. Configuration of the Appenders, Layouts and Filters that were provided in the Log4j 1 distribution will be redirected to their Log4j 2 counterparts. This means that although the while the behavior of these components will be similar they may not be exactly the same. For example, the XML generated by the XMLLayout may not exactly match the XML generated by the Log4j 1 XMLLayout.
In addition, Log4j 2 supports custom Log4j 1 Appenders, Filters, and Layouts with some constraints. Since the original Log4j 1 components are not present in Log4j 2 custom components that extend them will fail.
As support for Log4j 1 is an experimental feature one of the following steps must be taken to enable it: