log4j2：在运行时重新配置记录器的问题

Question

This is related to log4j2 version 2.13.2 .

We are consuming an API which comes with it's own logger configuration file say - log4j2_api.xml . As an application developer, we have our own log4j2.xml in the classpath.

The API we are consuming is internally loading log4j2 entities (loggers and appenders) from log4j2_api.xml . It looks like when that happens, our own configuration from log4j2.xml gets overwritten by log4j2_api.xml and our application produces no further logs.

Here is a brief sequence of events -

1. Application starts and log4j2.xml gets loaded from classpath.
2. Application proceeds with appropriate logging as expected.
3. First API call happens. Internally log4j2_api.xml gets loaded and API logging happens as per it's configuration.
4. Application receives the needed data from the API and proceeds further, but without desired logging.

My exepectation here is - if pre-loaded ( by initial configuration) loggers/appenders are found in the new configuration, they should be updated and other ones should remain untouched. And ofcourse, the newly configured loggers/appenders should get added.

Is this understanding correct?

Thanks in advance.

Configuration Files -

log4j2.xml

<Configuration status="warn">
    <Appenders>
        <RollingFile name="applicationAppender" fileName="sample-log-executor-2008.log" filePattern="sample-log-executor-2008-%i.log">      
            <PatternLayout>
                <pattern>[%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n</pattern>
            </PatternLayout>
            
            <Policies>
                <SizeBasedTriggeringPolicy size="5 MB" />
            </Policies>
        </RollingFile>
        
        <Console name="console_window" target="SYSTEM_OUT">
            <PatternLayout pattern="[%-5level] %d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %c{1} - %msg%n" />
        </Console>
    </Appenders>
    
    <Loggers>
        <Logger name="com.abc.samplecode" level="trace" additivity="false">
            <appender-ref ref="applicationAppender" level="trace" />
        </Logger>

        <Root level="error" additivity="false">
            <appender-ref ref="console_window" />
        </Root>
    </Loggers>
</Configuration>

log4j_api.xml

<Configuration>
    <Appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout
                pattern="%d %-5p [%t] %C (%F:%L) - %m%n" />
        </Console>
        
        <RollingFile name="xyzAPIAppender" fileName="xyzAPILog.log"
            filePattern="xyzAPILog-%i.log">
            <PatternLayout
                pattern="%d{MMM dd yyyy HH:mm:ss.SSS} %-5p [%t] (%27F:%-5L) - %m%n" />
            <Policies>
                <SizeBasedTriggeringPolicy size="5 MB" />
            </Policies>
            <DefaultRolloverStrategy max="10" />
        </RollingFile>
    </Appenders>
    
    <Loggers>
        <logger name="com.xyz.api" level="warn"
            additivity="false">
            <AppenderRef ref="xyzAPIAppender" />
        </logger>
    </Loggers>
</Configuration>

Answer 1

I suspect you are missing log4j2 core jar in your class path.

Please see the arch for more details http://logging.apache.org/log4j/2.x/faq.html#which_jars

Answer 2

From what you are describing the library you are consuming is calling Log4j to configure with its own configuration. This is very rude as it causes the problem you are running into. When it loads its configuration it is reconfiguring Log4j so your configuration is being removed.

You need to get more information on the library you are calling and find out how to get it to stop reinitializing Log4j.