Log4j2初探

1.新建module，log4j2-demo

2.修改pom.xml，增加log4j2依赖

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>log-study</artifactId>
        <groupId>com.lxcourse</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>log4j2-demo</artifactId>

    <dependencies>
        <!-- log4j 日志门面       -->
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-api</artifactId>
            <version>2.11.1</version>
        </dependency>
        <!-- log4j 日志实现-->
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>2.11.1</version>
        </dependency>
        <!-- junit-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <encoding>UTF-8</encoding>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

3.新建测试类

package com.lxcourse.log4j2;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.junit.Test;

public class Log4j2Demo {

    public static final Logger LOGGER = LogManager.getLogger(Log4j2Demo.class);

    @Test
    public void testQuick(){
        LOGGER.fatal("fatal");
        LOGGER.error("error");
        LOGGER.warn("warn");
        LOGGER.info("info");
        LOGGER.debug("debug");
        LOGGER.trace("trace");
    }
}

输出：

19:55:46.187 [main] FATAL com.lxcourse.log4j2.Log4j2Demo - fatal
19:55:46.190 [main] ERROR com.lxcourse.log4j2.Log4j2Demo - error

5.新增log4j2.xml

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" monitorInterval="5">
    <properties>
        <property name="LOG_HOME">/Users/doubledumbao/logs/logger</property>
    </properties>
    <Appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] [%-5level] %c{36}:%L --- %m%n" />
        </Console>
        <File name="file" fileName="${LOG_HOME}/myfile.log">
            <PatternLayout pattern="[%d{yyyy-MM-dd HH:mm:ss.SSS}] [%-5level] %l%c{36} - %m%n"/>
        </File>
        <RandomAccessFile name="accessFile" fileName="${LOG_HOME}/myAcclog.log">
            <PatternLayout pattern="[%d{yyyy-MM-dd HH:mm:ss.SSS}] [%-5level] %l%c{36} - %m%n"/>
        </RandomAccessFile>
        <RollingFile name="rollingFile" fileName="${LOG_HOME}/myrollog.log"
                     filePattern="${LOG_HOME}/$${date:yyyy-MM-dd}/myrollog-%d{yyyy-MM-dd-HH-mm}-%i.log">
            <ThresholdFilter level="debug" onMatch="ACCEPT" onMismatch="DENY"/>
            <PatternLayout pattern="[%d{yyyy-MM-dd HH:mm:ss.SSS}] [%-5level] %l%c{36} - %msg%n"/>
            <Policies>
                <OnStartupTriggeringPolicy/>
                <SizeBasedTriggeringPolicy size="10 MB"/>
                <TimeBasedTriggeringPolicy/>
            </Policies>
            <DefaultRolloverStrategy max="30"/>
        </RollingFile>
    </Appenders>
    <Loggers>
        <Root level="trace">
            <AppenderRef ref="Console"/>
        </Root>
    </Loggers>
</Configuration>

输出：

19:56:32.572 [main] [FATAL] com.lxcourse.log4j2.Log4j2Demo:13 --- fatal
19:56:32.575 [main] [ERROR] com.lxcourse.log4j2.Log4j2Demo:14 --- error
19:56:32.575 [main] [WARN ] com.lxcourse.log4j2.Log4j2Demo:15 --- warn
19:56:32.575 [main] [INFO ] com.lxcourse.log4j2.Log4j2Demo:16 --- info
19:56:32.575 [main] [DEBUG] com.lxcourse.log4j2.Log4j2Demo:17 --- debug
19:56:32.575 [main] [TRACE] com.lxcourse.log4j2.Log4j2Demo:18 --- trace

6.使用Slf4j门面+log4j2

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>log-study</artifactId>
        <groupId>com.lxcourse</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>log4j2-demo</artifactId>

    <dependencies>
        <!--  slf4j门面 -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.26</version>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-slf4j-impl</artifactId>
            <version>2.9.1</version>
        </dependency>

        <!-- log4j 日志门面       -->
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-api</artifactId>
            <version>2.11.1</version>
        </dependency>
        <!-- log4j 日志实现-->
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>2.11.1</version>
        </dependency>
        <!-- junit-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <encoding>UTF-8</encoding>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

7.异步日志

Log4j2提供了两种实现日志的方式，一个是通过AsyncAppender，一个是通过AsyncLogger，分别对应前面我们说的Appender组件和Logger组件。

注意:配置异步日志需要添加依赖

<!--异步日志依赖--> 
<dependency>
    <groupId>com.lmax</groupId>
    <artifactId>disruptor</artifactId>
    <version>3.3.4</version>
</dependency>

AsyncAppender方式

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" monitorInterval="5">
    <properties>
        <property name="LOG_HOME">/Users/doubledumbao/logs/logger</property>
    </properties>
    <Appenders>
        <Console name="Console" target="SYSTEM_ERR">
            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] [%-5level] %c{36}:%L --- %m%n"/>
        </Console>
        <File name="file" fileName="${LOG_HOME}/myfile.log">
            <PatternLayout pattern="[%d{yyyy-MM-dd HH:mm:ss.SSS}] [%-5level] %l%c{36} - %m%n"/>
        </File>
        <Async name="Async">
            <AppenderRef ref="file"/>
        </Async>
        <RandomAccessFile name="accessFile" fileName="${LOG_HOME}/myAcclog.log">
            <PatternLayout pattern="[%d{yyyy-MM-dd HH:mm:ss.SSS}] [%-5level] %l%c{36} - %m%n"/>
        </RandomAccessFile>
        <RollingFile name="rollingFile" fileName="${LOG_HOME}/myrollog.log"
                     filePattern="${LOG_HOME}/$${date:yyyy-MM-dd}/myrollog-%d{yyyy-MM-dd-HH-mm}-%i.log">
            <ThresholdFilter level="debug" onMatch="ACCEPT" onMismatch="DENY"/>
            <PatternLayout pattern="[%d{yyyy-MM-dd HH:mm:ss.SSS}] [%-5level] %l%c{36} - %msg%n"/>
            <Policies>
                <OnStartupTriggeringPolicy/>
                <SizeBasedTriggeringPolicy size="10 MB"/>
                <TimeBasedTriggeringPolicy/>
            </Policies>
            <DefaultRolloverStrategy max="30"/>
        </RollingFile>
    </Appenders>
    <Loggers>
        <Root level="trace">
            <AppenderRef ref="Console"/>
            <AppenderRef ref="Async" />
        </Root>
    </Loggers>
</Configuration>

AsyncLogger方式

AsyncLogger才是log4j2 的重头戏，也是官方推荐的异步方式。它可以使得调用Logger.log返回的

更快。你可以有两种选择:全局异步和混合异步。

全局异步就是，所有的日志都异步的记录，在配置文件上不用做任何改动，只需要添加一个

log4j2.component.properties 配置;

混合异步就是，你可以在应用中同时使用同步日志和异步日志，这使得日志的配置方式更加灵活。

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" monitorInterval="5">
    <properties>
        <property name="LOG_HOME">/Users/doubledumbao/logs/logger</property>
    </properties>
    <Appenders>
        <Console name="Console" target="SYSTEM_ERR">
            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] [%-5level] %c{36}:%L --- %m%n"/>
        </Console>
        <File name="file" fileName="${LOG_HOME}/myfile.log">
            <PatternLayout pattern="[%d{yyyy-MM-dd HH:mm:ss.SSS}] [%-5level] %l%c{36} - %m%n"/>
        </File>
        <!--        <Async name="Async">-->
        <!--            <AppenderRef ref="file"/>-->
        <!--        </Async>-->
        <RandomAccessFile name="accessFile" fileName="${LOG_HOME}/myAcclog.log">
            <PatternLayout pattern="[%d{yyyy-MM-dd HH:mm:ss.SSS}] [%-5level] %l%c{36} - %m%n"/>
        </RandomAccessFile>
        <RollingFile name="rollingFile" fileName="${LOG_HOME}/myrollog.log"
                     filePattern="${LOG_HOME}/$${date:yyyy-MM-dd}/myrollog-%d{yyyy-MM-dd-HH-mm}-%i.log">
            <ThresholdFilter level="debug" onMatch="ACCEPT" onMismatch="DENY"/>
            <PatternLayout pattern="[%d{yyyy-MM-dd HH:mm:ss.SSS}] [%-5level] %l%c{36} - %msg%n"/>
            <Policies>
                <OnStartupTriggeringPolicy/>
                <SizeBasedTriggeringPolicy size="10 MB"/>
                <TimeBasedTriggeringPolicy/>
            </Policies>
            <DefaultRolloverStrategy max="30"/>
        </RollingFile>
    </Appenders>
    <Loggers>
        <AsyncLogger name="com.lxcourse" level="trace"
                     includeLocation="false" additivity="false">
            <AppenderRef ref="file"/>
        </AsyncLogger>
        <Root level="trace">
            <AppenderRef ref="file"/>
            <!-- <AppenderRef ref="Async" />-->
        </Root>
    </Loggers>
</Configuration>

如上配置: com.lxcourse 日志是异步的，root日志是同步的。

使用异步日志需要注意的问题:

如果使用异步日志，AsyncAppender、AsyncLogger和全局日志，不要同时出现。性能会和 AsyncAppender一致，降至最低。
设置includeLocation=false ，打印位置信息会急剧降低异步日志的性能，比同步日志还要慢。

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原文地址：https://www.cnblogs.com/zhaoran8775/p/12990763.html