Ans. Properties can be defined by a properties file or by an XML file. Log4j looks for a file named log4j.xml and then for a file named log4j.properties. Both must be placed in the src folder.

The property file is less verbose than an XML file. The XML requires the log4j.dtd to be placed in the source folder as well. The XML requires a dom4j.jar which might not be included in older Java versions.

The properties file does not support some advanced configuration options like Filters, custom ErrorHandlers and a special type of appenders, i.e. AsyncAppender. ErrorHandlers defines how errors in log4j itself are handled, for example badly configured appenders. Filters are more interesting. From the available filters, I think that the level range filter is really missing for property files.

Posted on Jul 26, 2014 by Johny Verma