今天和两个同事讨论Log4j，他们都需要解决一个问题，怎么分开输出Logger。这么讲不清楚，举个例子：
package com.gmail.at.ankyhe.log4jtest;
import org.apache.log4j.Logger;
public class ClassA {
private static Logger logger = Logger.getLogger(ClassA.class.getName());
public ClassA() {
logger.info("ENTER ClassA()");
}
public void foo() {
logger.info("foo()");
bar();
}
public void bar() {
Logger myLog = Logger.getLogger("bar");
myLog.debug("bar()D");
myLog.info("bar()I");
}
}
我希望bar可以输出到一个地方，其他的logger可以输出到一个地方。一般的配置文件如下：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd"> <log4j:configuration xmlns:log4j='http://jakarta.apache.org/log4j/' > <appender name="myConsole" class="org.apache.log4j.ConsoleAppender">
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern"
value="[%d{dd HH:mm:ss,SSS\} %-5p] [%t] %c{2\} - %m%n" />
</layout>
</appender> <appender name="myFile" class="org.apache.log4j.RollingFileAppender">
<param name="File" value="xml.log" />
<param name="Append" value="false" />
<param name="MaxBackupIndex" value="10" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%p (%c:%L)- %m%n" />
</layout>
</appender> <logger name="bar">
<level value="info" />
<appender-ref ref="myConsole" />
</logger> <root>
<priority value="debug" />
<appender-ref ref="myFile" />
</root>
</log4j:configuration>
这样会发现一个问题，myLog的输出又会在文件，又会在终端。原因在Log4J官方的Introduction讲的很清楚：
http://logging.apache.org/log4j/1.2/manual.html 搜索Appender Additivity. 我解释一下就是默认情况下bar会集成root的输出。知道了原因，那怎么修改就简单了。
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd"> <log4j:configuration xmlns:log4j='http://jakarta.apache.org/log4j/' > <appender name="myConsole" class="org.apache.log4j.ConsoleAppender">
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern"
value="[%d{dd HH:mm:ss,SSS\} %-5p] [%t] %c{2\} - %m%n" />
</layout>
</appender> <appender name="myFile" class="org.apache.log4j.RollingFileAppender">
<param name="File" value="xml.log" />
<param name="Append" value="false" />
<param name="MaxBackupIndex" value="10" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%p (%c:%L)- %m%n" />
</layout>
</appender> <logger name="bar" additivity="false">
<level value="info" />
<appender-ref ref="myConsole" />
</logger> <root>
<priority value="debug" />
<appender-ref ref="myFile" />
</root>
</log4j:configuration>
唯一的区别是在bar那个logger后面加了一个 additivity="false"。我试了一下，可以按照要求工作。这是xml的配置，一般的property的配置如下：
log4j.rootLogger=DEBUG, FA
log4j.category.bar = INFO, CA
log4j.additivity.bar = false #Console Appender log4j.appender.CA=org.apache.log4j.ConsoleAppender
log4j.appender.CA.layout=org.apache.log4j.PatternLayout
log4j.appender.CA.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n #File Appender
log4j.appender.FA=org.apache.log4j.FileAppender
log4j.appender.FA.File=property.log
log4j.appender.FA.layout=org.apache.log4j.PatternLayout
log4j.appender.FA.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n