使用slf4j + Log4j2构建日志

一、背景

Log4j 1.x 在高并发情况下出现死锁导致cpu使用率异常飙升，而Log4j2.0基于LMAX Disruptor的异步日志在多线程环境下性能会远远优于Log4j 1.x和logback（官方数据是10倍以上），这里分享slf4j + Log4j2的使用方法。

二、步骤

1、pom.xml

删除以往依赖Log4j1.x的依赖项，比如slf4j-log4j12、log4j等包。

可以到项目的根目录，执行：mvn dependency:tree > tree.log ，查看之后 cat tree.log | grep log4j查找。

<exclusions>
<exclusion>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
</exclusion>
<exclusion>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
</exclusion>
</exclusions>

然后在工程的pom.xml新增以下log4j2的依赖关系：

<!-- Logging use log4j2-->
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.13</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>jcl-over-slf4j</artifactId>
<version>1.7.13</version>
<scope>runtime</scope>
</dependency>

<!--核心log4j2jar包-->
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-api</artifactId>
<version>2.4.1</version>
</dependency>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-core</artifactId>
<version>2.4.1</version>
</dependency>
<!--用于与slf4j保持桥接-->
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-slf4j-impl</artifactId>
<version>2.4.1</version>
</dependency>
<!--web工程需要包含log4j-web，非web工程不需要-->
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-web</artifactId>
<version>2.4.1</version>
<scope>runtime</scope>
</dependency>

<!--需要使用log4j2的AsyncLogger需要包含disruptor-->
<dependency>
<groupId>com.lmax</groupId>
<artifactId>disruptor</artifactId>
<version>3.2.0</version>
</dependency>

2、web.xml

web工程的web.xml文件中添加（Servlet3.0不需要）：

<!--log4j2-->
<!--对于log4j2，Servlet2.5以前的版本需要-->
<listener>
<listener-class>org.apache.logging.log4j.web.Log4jServletContextListener</listener-class>
</listener>
<filter>
<filter-name>log4jServletFilter</filter-name>
<filter-class>org.apache.logging.log4j.web.Log4jServletFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>log4jServletFilter</filter-name>
<url-pattern>/*</url-pattern>
<dispatcher>REQUEST</dispatcher>
<dispatcher>FORWARD</dispatcher>
<dispatcher>INCLUDE</dispatcher>
<dispatcher>ERROR</dispatcher>
</filter-mapping>

3、log4j2.xml

log4j2不再支持properties文件了，只支持xml，json或是yaml。

默认不指定位置，可以放在src/main/resources下。如果需要自定义位置，需要在上面的web.xml中添加

<context-param>
<param-name>log4jConfiguration</param-name>
<param-value>/WEB-INF/classes/log4j2.xml</param-value>
</context-param>

下面是一个log4j2.xml的demo

<?xml version="1.0" encoding="UTF-8"?>

<Configuration status="off" monitorInterval="1800">

<properties>
<property name="LOG_HOME">/opt/logs/gct/shoppromo/logs</property>
<property name="ERROR_LOG_FILE_NAME">error</property>
</properties>

<Appenders>
<Console name="Console" target="SYSTEM_OUT">
<PatternLayout pattern="%d %-5p (%F:%L) - %m%n" />
</Console>

<RollingRandomAccessFile name="ErrorLog"
fileName="${LOG_HOME}/${ERROR_LOG_FILE_NAME}.log"
filePattern="${LOG_HOME}/${ERROR_LOG_FILE_NAME}.log.%d{yyyy-MM-dd}.gz">
<PatternLayout
pattern="%d %-5p (%F:%L) - %m%n"/>
<Policies>
<TimeBasedTriggeringPolicy/>
<SizeBasedTriggeringPolicy size="100 MB"/>
</Policies>
<DefaultRolloverStrategy max="20"/>
</RollingRandomAccessFile>

</Appenders>

<Loggers>
<!-- 3rdparty Loggers -->
<logger name="org.springframework.core" level="info">
</logger>
<logger name="org.springframework.beans" level="info">
</logger>
<logger name="org.springframework.context" level="info">
</logger>
<logger name="org.springframework.web" level="info">
</logger>

<logger name="com.meituan.gct.shop.promo" level="error" includeLocation="true" additivity="false">
<appender-ref ref="ErrorLog"/>
<appender-ref ref="Console"/>
</logger>

<root level="info" includeLocation="true">
<appender-ref ref="Console"/>
</root>
</Loggers>
</Configuration>

4、代码示例

import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.RequestMapping;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

@Controller
@RequestMapping("/api/")
public class TestController {
private static Logger log = LogManager.getLogger(TestController.class.getName());

@RequestMapping(value = "/test")
public String test(
HttpServletRequest request, HttpServletResponse response, ModelMap modelMap) {

log.info("你好啊");
log.debug("我是debug");
log.error("错了");
log.trace("这是什么");

modelMap.put("s", "ok");
return "string";
}

}

注意：在JVM启动参数中增加 -DLog4jContextSelector=org.apache.logging.log4j.core.async.AsyncLoggerContextSelector 开启异步日志