如何配置 log4j2.xml 从文件到标准输出？

Question

Here is my current log4j2.xml file :

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="info">
<Properties>
    <Property name="logFilename">abc</Property>
    <Property name="metricsLogFilename">abc-metrics</Property>
    <Property name="pattern">%d [%X{idreq} %X{iduser} %X{codeenv}] %-5p
        [%c{1}] : %m%n</Property>
    <Property name="metricsPattern">%d : %m%n</Property>
    <Property name="level">${sys:LOG4J_LEVEL:-info}</Property>
</Properties>
<Appenders>
    <Console name="console" target="SYSTEM_OUT" follow="true"  >
    <PatternLayout pattern="${pattern}" />
    </Console>
    <RollingRandomAccessFile name="file"
        fileName="${tex:appLogFilePath}${logFilename}.log"
        filePattern="${tex:appLogFilePath}${logFilename}-%i.log.gz">
        <PatternLayout pattern="${pattern}" />
        <Policies>
            <SizeBasedTriggeringPolicy size="10MB" />
        </Policies>
        <DefaultRolloverStrategy max="1" />
    </RollingRandomAccessFile>
    <RollingRandomAccessFile name="metricsFile"
        fileName="${tex:appLogFilePath}${metricsLogFilename}.log"
        filePattern="${tex:appLogFilePath}${metricsLogFilename}-%i.log.gz"
        immediateFlush="false">
        <PatternLayout pattern="${metricsPattern}" />
        <Policies>
            <SizeBasedTriggeringPolicy size="10MB" />
        </Policies>
        <DefaultRolloverStrategy max="1" />
    </RollingRandomAccessFile>
</Appenders>
<Loggers>
    <Logger name="com.myClass.common" level="info" additivity="false">
        <AppenderRef ref="console" />
        <AppenderRef ref="file" />
    </Logger>
        <Logger name="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping" level="${level}" additivity="false">
        <AppenderRef ref="console" />
        <AppenderRef ref="file" />
    </Logger>
    <Logger name="metrics" level="info" additivity="false">
        <AppenderRef ref="metricsFile" />
    </Logger>
    <Root level="${level}">
        <AppenderRef ref="console" />
        <AppenderRef ref="file" />
    </Root>
</Loggers>

I want to switch to stdout instead of file logs. What should I change ? (I've never used log4j)

The reason why I want to have it stdout is because I'll need to deploy my app on heroku, and on heroku we need to use system out logging.

Answer 1

As per current configuration, except metrics, your are logging at both places - in a file as well as on console. For metrices, you are logging in file only.

If you can want to log only at console, remove other appender and their references from logger configuration. For metrices, you have to refer console appender.

Update file may look like -

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="info">
<Properties>
    <Property name="pattern">%d [%X{idreq} %X{iduser} %X{codeenv}] %-5p
        [%c{1}] : %m%n</Property>
    <Property name="level">${sys:LOG4J_LEVEL:-info}</Property>
</Properties>
<Appenders>
    <Console name="console" target="SYSTEM_OUT" follow="true"  >
        <PatternLayout pattern="${pattern}" />
    </Console>
</Appenders>
<Loggers>
    <Logger name="com.myClass.common" level="info" additivity="false">
        <AppenderRef ref="console" />
    </Logger>
        <Logger name="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping" level="${level}" additivity="false">
        <AppenderRef ref="console" />
    </Logger>
    <Logger name="metrics" level="info" additivity="false">
        <AppenderRef ref="console" />
    </Logger>
    <Root level="${level}">
        <AppenderRef ref="console" />
    </Root>
</Loggers>