为什么我在Log4J中得到双倍输出？

Question

I am working on a Java Spring project and I want to log WARNS from every package and only INFO from my packages.

I don't know why Log4J is giving me double line output for my packages.

Can someone please tell me why

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

    <appender name="console" class="org.apache.log4j.ConsoleAppender">
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern" value="%d [%t] %-5p %c - %m%n"/>
        </layout>
    </appender>


    <logger name="com.xxxxx.mongodb">
        <level value="INFO"/>
        <appender-ref ref="console" />
    </logger>

    <root>
        <priority value="WARN"/>
        <appender-ref ref="console"/>
    </root>
</log4j:configuration>

Answer 1

Because your logger inherits the appenders from root logger.

The docs for log4j state:

The output of a log statement of logger C will go to all the appenders in C and its ancestors. This is the meaning of the term "appender additivity".

However, if an ancestor of logger C, say P, has the additivity flag set to false, then C's output will be directed to all the appenders in C and its ancestors upto and including P but not the appenders in any of the ancestors of P.

Loggers have their additivity flag set to true by default.

Answer 2

Add

additivity="false"

attribute to the logger what is producing double output.