Some log4j2.xml examples, just for self-reference

P.S Tested with Log4j 2.11.2

1. ConsoleAppender

Logs to console.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="DEBUG">
    <Appenders>
        <Console name="LogToConsole" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
        </Console>
    </Appenders>
    <Loggers>
		<!-- avoid duplicated logs with additivity=false -->
        <Logger name="com.mkyong" level="debug" additivity="false">
            <AppenderRef ref="LogToConsole"/>
        </Logger>
        <Root level="error">
            <AppenderRef ref="LogToConsole"/>
        </Root>
    </Loggers>
</Configuration>

2. FileAppender

Logs to a file.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="DEBUG">
    <Appenders>
        <File name="LogToFile" fileName="logs/app.log">
            <PatternLayout>
                <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
            </PatternLayout>
        </File>
    </Appenders>
    <Loggers>
        <!-- avoid duplicated logs with additivity=false -->
        <Logger name="com.mkyong" level="debug" additivity="false">
            <AppenderRef ref="LogToFile"/>
        </Logger>
        <Root level="error">
            <AppenderRef ref="LogToFile"/>
        </Root>
    </Loggers>
</Configuration>

3. ConsoleAppender + FileAppender

Logs to both console and file.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="DEBUG">
    <Appenders>
        <Console name="LogToConsole" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
        </Console>
        <File name="LogToFile" fileName="logs/app.log">
            <PatternLayout>
                <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
            </PatternLayout>
        </File>
    </Appenders>
    <Loggers>
        <Logger name="com.mkyong" level="debug" additivity="false">
            <AppenderRef ref="LogToFile"/>
            <AppenderRef ref="LogToConsole"/>
        </Logger>
        <Logger name="org.springframework.boot" level="error" additivity="false">
            <AppenderRef ref="LogToConsole"/>
        </Logger>
        <Root level="error">
            <AppenderRef ref="LogToFile"/>
            <AppenderRef ref="LogToConsole"/>
        </Root>
    </Loggers>
</Configuration>

4 RollingFileAppender

Rotate log file. If file size > 10m or the current date is different with the log file time stamp, create archives.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="DEBUG">
    <Appenders>
        <Console name="LogToConsole" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
        </Console>
        <RollingFile name="LogToRollingFile" 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>
            <TimeBasedTriggeringPolicy />
            <SizeBasedTriggeringPolicy size="10 MB"/>
        </Policies>
    </RollingFile>
    </Appenders>
    <Loggers>
        <!-- avoid duplicated logs with additivity=false -->
        <Logger name="com.mkyong" level="debug" additivity="false">
            <AppenderRef ref="LogToRollingFile"/>
        </Logger>
        <Root level="error">
            <AppenderRef ref="LogToConsole"/>
        </Root>
    </Loggers>
</Configuration>

By default, it will create up to 7 archives on the same day.

We can override the default 7 archives with this DefaultRolloverStrategy

	<RollingFile name="LogToRollingFile" 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>
			<TimeBasedTriggeringPolicy/>
			<SizeBasedTriggeringPolicy size="10 MB"/>
		</Policies>
		<DefaultRolloverStrategy max="10"/>
	</RollingFile>

5 RollingRandomAccessFileAppender

Similar to the RollingFileAppender, but faster.

	<RollingRandomAccessFile name="LogToRollingRandomAccessFile" 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>
			<TimeBasedTriggeringPolicy/>
			<SizeBasedTriggeringPolicy size="1 MB"/>
		</Policies>
		<DefaultRolloverStrategy max="10"/>
	</RollingRandomAccessFile>

6 SMTPAppender

Need javax.mail to send email.

	<dependency>
		<groupId>com.sun.mail</groupId>
		<artifactId>javax.mail</artifactId>
		<version>1.6.2</version>
	</dependency>

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
    <Appenders>
        <RollingRandomAccessFile name="LogToRollingRandomAccessFile" 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>
                <TimeBasedTriggeringPolicy/>
                <SizeBasedTriggeringPolicy size="1 MB"/>
            </Policies>
            <DefaultRolloverStrategy max="10"/>
        </RollingRandomAccessFile>
        <SMTP name="LogToMail" subject="Error Log From Log4j"
              from="from@DOMAIN"
              to="to@DOMAIN"
              smtpHost="smtp.mailgun.org"
              smtpPort="25"
              smtpUsername="abc"
              smtpPassword="123"
              bufferSize="100">
        </SMTP>
    </Appenders>
    <Loggers>
        <Logger name="com.mkyong" level="debug" additivity="false">
            <AppenderRef ref="LogToRollingRandomAccessFile"/>
            <AppenderRef ref="LogToConsole"/>
        </Logger>
        <Root level="error">
            <AppenderRef ref="LogToMail"/>
        </Root>
    </Loggers>
</Configuration>

Sample email