log4j2+slf4j使用案例

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本文介绍如何通过引入必要的依赖包、配置web.xml和log4j2.xml文件来实现日志记录功能，并展示了如何在代码中使用Log4j2进行日志输出。

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1、引入jar包

<slf4j.version>1.7.12</slf4j.version>
<log4j2.version>2.3</log4j2.version>

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>${slf4j.version}</version>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-api</artifactId>
    <version>${log4j2.version}</version>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
    <version>${log4j2.version}</version>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-slf4j-impl</artifactId>
    <version>${log4j2.version}</version>
</dependency

2、设置web.xml文件log监听器

<listener>
   <listener-class>org.springframework.web.util.Log4jConfigListener</listener-class>
</listener>
3、新建log4j2.xml文件并存放在resource跟路径下
同步追加配置：

<?xml version="1.0" encoding="UTF-8"?>
<!-- Don't forget to set system property
-DLog4jContextSelector=org.apache.logging.log4j.core.async.AsyncLoggerContextSelector
     to make all loggers asynchronous. -->
<Configuration status="trace" >
    <Appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
        </Console>
        <!--这个会打印出所有的信息，每次大小超过size，则这size大小的日志会自动存入按年份-月份建立的文件夹下面并进行压缩，作为存档-->
        <RollingFile name="RollingFile" fileName="logs/server.log"
                     filePattern="logs/$${date:yyyy-MM}/server-%d{MM-dd-yyyy}-%i.log.gz">
            <PatternLayout pattern="%d{yyyy-MM-dd 'at' HH:mm:ss z} %-5level %class{36} %L %M - %msg%xEx%n"/>
            <SizeBasedTriggeringPolicy size="50MB"/>
        </RollingFile>
    </Appenders>
    <Loggers>
        <Root level="info">
            <AppenderRef ref="Console"/>
            <appender-ref ref="RollingFile"/>
        </Root>
    </Loggers>
</Configuration>
异步追加配置：
<?xml version="1.0" encoding="UTF-8"?> 
<!-- Don't forget to set system property-DLog4jContextSelector=org.apache.logging.log4j.core.async.AsyncLoggerContextSelector     to make all loggers asynchronous. --> 
<Configuration status="WARN">  
<Appenders>    
<!-- Async Loggers will auto-flush in batches, so switch off immediateFlush. -->    
	<RandomAccessFile name="RandomAccessFile" fileName="async.log" immediateFlush="false" append="false">      
	<PatternLayout>        
		<Pattern>%d %p %c{1.} [%t] %m %ex%n</Pattern>      
	</PatternLayout>    
	</RandomAccessFile>  
</Appenders>  
<Loggers>    
	<Root level="info" includeLocation="false">      
		<AppenderRef ref="RandomAccessFile"/>    
	</Root>  
</Loggers>
</Configuration>

4、代码中使用log4j2

导入日志相关类，注意要导入slf4j对应的logger和loggerFactory;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


实例化日志对象
private static Logger logger = LoggerFactory.getLogger(UserController.class);
使用日志打印

log.info("hello world!");




5、添加jvm log4j2相关参数(目的使日志异步追加)

-DLog4jContextSelector=org.apache.logging.log4j.core.async.AsyncLoggerContextSelector