log4j 2 - configuration issue

Question

I am trying to configure log4j 2.0 to report logs.

My config is saved as log4j2.xml and this is its content:

  <?xml version="1.0" encoding="UTF-8"?>
  <configuration name="PRODUCTION" status="OFF">

    <appenders>
        <RollingFile name="MyFileAppender" 
            fileName="../Logs/app.log" 
            filePattern="../Logs/$${date:yyyy-MM}/app-%d{MM-dd-yyyy}-%i.log.gz">
            <PatternLayout>
                <pattern>%d %p %C{1.} [%t] %m%n</pattern>
            </PatternLayout>
            <Policies>
                <OnStartupTriggeringPolicy />
                <TimeBasedTriggeringPolicy interval="6" modulate="true"/>
                <SizeBasedTriggeringPolicy size="250 MB"/>
            </Policies>
        </RollingFile>
    </appenders>

    <loggers>
        <root level="trace">
            <appender-ref ref="MyFileAppender"/>
        </root>
    </loggers>

 </configuration>

It exists in the classpath of the project and I tried putting it in many other directories..

I created a logger in the code like so:

    Logger          logger = LogManager.getLogger(MyClass.class.getName());
    logger.info("test");

And nothing is written and no file is created. When I debug the code I see that the logger is the default logger(console).

Answer 1

Actually This is a straight forward process. Two main classes of Log4j 2 are as follows that you need to import like this:

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

Now get a Logger instance by using this code.

    private static final Logger logger = LogManager.getLogger();

Note I didn't specified the class name to getLogger() method as a parameter. Log4j 2 automatically figures it out.

Now you can use any of the info(), trace(), debug(), warn(), error(), fatal() method from the Logger class. But to get the output from all of these methods you'll need a XML configuration file. By default Log4j 2 only produces output from the error() and fatal() methods.

Configuration file is as follows:

    <?xml version="1.0" encoding="UTF-8"?>
    <Configuration status="WARN">
        <Appenders>
            <File name="MyCustomLogFile" fileName="/home/me/mylogfile.log">
                <PatternLayout>
                    <Pattern>%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n</Pattern>
                </PatternLayout>
            </File>
            <Console name="Console" target="SYSTEM_OUT">
                <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
            </Console>
        </Appenders>
        <Loggers>
            <Root level="all">
                <AppenderRef ref="MyCustomLogFile"/>
                <!--<AppenderRef ref="Console"/>-->
            </Root>
        </Loggers>
    </Configuration>

Save this file with any name any where. I use Log4j2.xml as name. Now you'll need this file to be put in classpath, which you can do by passing a system property when running the program as follows:

    java -Dlog4j.configurationFile=/path/to/xml/configuration/file/Log4j2.xml MyMainClass

And you've done it. Logging will be right away on your console.

Special Notes:

• In XML file I've provided 2 appenders: A file and a console. You can see that you just need to uncomment the commented AppenderRef tag to get output in a file instead of console.

• You can also provide an environment variable as a system property. Log4j 2 will read the configuration file from the environment variable first and then in -D argument if not found an environment variable.

Have fun with logging. :-)