Using a XML File (log4j2.xml) to configure Log4j 2

TIP : To use custom log4j files. (Rather default "log4j2.xml" thingie). It might be useful to have multiple configurations in some instances.

Just in case if any one using maven and wish to configure log4j2, Here is what you need in your pom.xml :

                <systemProperties>
                    <property>
                        <name>/log4j.configuration</name>
                        <value>.../../Foo-log4j.xml</value>
                    </property>
                </systemProperties>

By default, "log4j2.xml" is the file name expected. But however, we can override that by setting log4j.configuration system property. In the above example, I have used custom configuration file as "Foo-log4j.xml".

You can do the same via CLI :

-Dlog4j.configuration="Foo-log4j.xml"

Important: make sure the name of the configuration file is log4j2.xml (note the 2 before the period) as opposed to log4j.xml

My guess is nothing's happening because nothing is logged using the error level. You may want to try adding another logger like so:

<logger name="com.foo.Bar" level="trace">
  <appender-ref ref="Console"/>
</logger>

Looks like the Configuration section might be a good resource.

To elaborate further, you're specifying a logger with the level set to "error":

<root level="error">
  <appender-ref ref="Console"/>
</root>

This means that only the messages logged using Level.ERROR will show up in the log. Adding a logger with a less restrictive level will allow for more messages to appear in the log. I recommend taking a look at the Architecture section of the manual (if you scroll down the page you'll see the table that explains logging levels). Alternatively, you could just change the level of the root logger to trace (instead of adding a new logger)

Given the configuration you specified, executing the code below yields something like 13:27:50.244 [main] ERROR com.example.Log4j2Tester - testing ERROR level

package com.example;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class Log4j2Tester {
    private static final Logger LOG = LogManager.getLogger(Log4j2Tester.class);

    public static void main(String[] args) {
        LOG.error("testing ERROR level");

//if you change the level of root logger to 'trace'
//then you'll also see something like
//    13:27:50.244 [main] TRACE com.example.Log4j2Tester - exiting application
        LOG.trace("exiting application");
    }
}