log4j2

1、Eclipse新建一个Maven项目

2、修改pom.xml文件，代码如下，这里主要添加了log4j2的依赖log4j-api和log4j-core

<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">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.wyl.app</groupId>
  <artifactId>MainApp</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>MainApp</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.apache.logging.log4j</groupId>
        <artifactId>log4j-api</artifactId>
        <version>2.13.3</version>
    </dependency>
    <dependency>
        <groupId>org.apache.logging.log4j</groupId>
        <artifactId>log4j-core</artifactId>
        <version>2.13.3</version>
    </dependency>
  </dependencies>
</project>

3、在src/main/java目录下新建log4j2.xml

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
  <properties>
    <property name="error-file">./log4j2learn.txt</property>
    <Property name="console-pattern">%d{yyyy-MM-dd HH:mm:ss.SSS} [%t] [%level] %logger{36} - %msg%n</Property>
  </properties>
  <Appenders>
    <Console name="Console" target="SYSTEM_OUT">
      <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
    </Console>
    
    <File name="LogFile" fileName="${error-file}" createOnDemand="true">
      <PatternLayout pattern="${console-pattern}" />
    </File>
    
  </Appenders>
  
  <Loggers>
    <Root level="trace">
      <AppenderRef ref="Console"/>
      <AppenderRef ref="LogFile"/>
    </Root>
  </Loggers>
  
</Configuration>

这里可以通过修改level的级别，控制日志的输出级别

4、在主程序中使用

package com.wyl.app.MainApp;

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

/**
 * Hello world!
 *
 */
public class App 
{	
	private static final Logger logger  = LogManager.getLogger(App.class.getName());
	
	// 按照从低到高为：ALL < TRACE < DEBUG < INFO < WARN < ERROR < FATAL < OFF
	// 程序会打印高于或等于所设置级别的日志，设置的日志等级越高，打印出来的日志就越少。
    public static void main( String[] args)
    {
    	logger.trace("trace");
    	logger.debug("debug");
    	logger.info("info");
    	logger.warn("warn");
    	logger.error("error");
    }
}