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log4j2入门hello world

1.什么是log4j2

(1)log4j

log4j是apache的一个开源项目,表示log for java.是一个日志工具,可以将日志信息输出到文件,控制台等其他地方 ,还可以定义日志的输出格式,另外还有日志级别的区分,可通过配置文件去配置输出格式,输出目的地等信息.

(2)log4j2

log4j2从名字就知道了,是log4j的升级版本,性能有了很大提升,增加了很多新特性(如自定义级别,lambda表达式)与新的API,直接与tomcat等服务器集成.

3.VScode下使用log4j2(不用Maven

(1)准备jar包

点击这里下载

log4j2入门hello world

作者用的是win10,下载zip.

(2)准备插件

搜索安装:Eclipse New Java Project

log4j2入门hello world

(3)创建项目

ctrl+shift+p调出命令面板,输入new java project

log4j2入门hello world

项目名

log4j2入门hello world

JavaSE版本

log4j2入门hello world

创建完毕.

log4j2入门hello world

(4)设置jar包路径

在项目根路径下新建lib文件夹,把下载的

log4j2入门hello world

这两个jar包放进去.

下一步设置.classpath.

添加

<classpathentry kind="lib" path="lib/log4j-api-2.12.1.jar" />
<classpathentry kind="lib" path="lib/log4j-core-2.12.1.jar" />

(5)新建测试文件

src下直接建立test.java

test.java:

import org.apache.logging.log4j.*;

public class test
{
    private final static Logger logger = LogManager.getLogger(test.class.getName());
    public static void main(String[] args) {
        logger.info("info");
        logger.error("error");
        logger.debug("debug");
        logger.trace("trace");
        logger.fatal("fatel");
    }
}

(6)运行

点击main上的Run

log4j2入门hello world

结果:

log4j2入门hello world

输出了fatel与error信息.

另外还提示了没有找到log4j2配置文件,使用默认的配置文件,默认输出到控制台.

(7)创建配置文件使其输出更多信息

src下创建log4j2.xml配置文件.

log4j2入门hello world

log4j2的配置文件只能是.xml或.json或.jsn文件,默认会在classpath下寻找(在这里classpath相当于图中的src).

默认情况下系统选择配置文件的优先级如下:

1.classpath下名为 log4j-test.json 或者log4j-test.jsn文件
2.classpath下名为 log4j2-test.xml
3.classpath下名为 log4j.json 或者log4j.jsn文件
4.classpath下名为 log4j2.xml

这里使用log4j2.

xml.log4j2.xml如下:

<?xml version="1.0" encoding="UTF-8"?>    
<configuration status="OFF">    
  <appenders>    
    <Console name="Console" target="SYSTEM_OUT">    
      <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>    
    </Console>    
  </appenders>    
  <loggers>    
    <logger name="test" level="info" additivity="false">    
      <appender-ref ref="Console"/>    
    </logger>    
    <root level="info">    
      <appender-ref ref="Console"/>    
    </root>    
  </loggers>    
</configuration>

Logger三个主要的组件为

logger(记录器)
appender(输出目的地)
layout(布局,定义日志的格式)

<appenders>了输出目的地,<Console>表示控制台,<PatternLayout>定义了布局,里面的布局表示时间格式(%d,HH:mm:ss.SSS),接着是日志线程名(%t),%-5表示最小长度为5左对齐,level表示输出日志级别.

%logger表示输出logger名称.

%m是%msg与%message的缩写,表示输出应用提供的与记录事件有关的信息.

%n表示换行.

<loggers>定义的logger与logger使用的appender.root为log默认的输出形式,如果一个类的没有明确loggers中的输出格式就会采用root的格式.

(8)再次运行

没有之前的"没有配置文件"的提示了.

log4j2入门hello world

4.VScode下使用log4j2(带Maven)

(1)创建maven项目

使用插件maven for java创建,命令面板(ctrl+shift+p)输入.

log4j2入门hello world

选择quickstart.

log4j2入门hello world

选择版本.

log4j2入门hello world

最后选择项目路径即可.

在控制台中vscode会下载相关文件,然后会提示以交互模式创建:

log4j2入门hello world

这里等一会就好了.

然后会提示输入一些值.

log4j2入门hello world

ok.

(2)在pom.xml配置依赖

在<dependencies>中添加如下代码:

<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-api</artifactId>
    <version>2.12.1</version>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
    <version>2.12.1</version>
</dependency>

以下是完整的pom.xml:

<?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">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>test</artifactId>
    <version>1.0-SNAPSHOT</version>

    <name>test</name>
    <!-- FIXME change it to the project's website -->
    <url>http://www.example.com</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.7</maven.compiler.source>
        <maven.compiler.target>1.7</maven.compiler.target>
    </properties>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-api</artifactId>
            <version>2.12.1</version>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>2.12.1</version>
        </dependency>
    </dependencies>


    <build>
        <pluginManagement>
            <!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
            <plugins>
                <!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle -->
                <plugin>
                    <artifactId>maven-clean-plugin</artifactId>
                    <version>3.1.0</version>
                </plugin>
                <!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging -->
                <plugin>
                    <artifactId>maven-resources-plugin</artifactId>
                    <version>3.0.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <version>3.8.0</version>
                </plugin>
                <plugin>
                    <artifactId>maven-surefire-plugin</artifactId>
                    <version>2.22.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-jar-plugin</artifactId>
                    <version>3.0.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-install-plugin</artifactId>
                    <version>2.5.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-deploy-plugin</artifactId>
                    <version>2.8.2</version>
                </plugin>
                <!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle -->
                <plugin>
                    <artifactId>maven-site-plugin</artifactId>
                    <version>3.7.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-project-info-reports-plugin</artifactId>
                    <version>3.0.0</version>
                </plugin>
            </plugins>
        </pluginManagement>
    </build>
</project>

右键选择Update project configuration.

log4j2入门hello world

(3)创建log4j2.xml

在java目录下新建log4j2.xml.

log4j2入门hello world

<?xml version="1.0" encoding="UTF-8"?>
<configuration status="OFF">
    <appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
        </Console>
    </appenders>
    <loggers>
        <logger name="com.example.App" level="info" additivity="false">
            <appender-ref ref="Console"/>
        </logger>
        <root level="info">
            <appender-ref ref="Console"/>
        </root>
    </loggers>
</configuration>

(4)修改测试类

修改默认的App.java.

package com.example;
import org.apache.logging.log4j.*;
public class App
{
    private static final Logger logger = LogManager.getLogger(App.class.getName());
    public static void main( String[] args )
    {
        logger.info("info");
        logger.error("error");
        logger.debug("debug");
        logger.trace("trace");
        logger.fatal("fatel");
    }
}

(5)测试

run即可.

log4j2入门hello world

5.IDEA下使用log4j2(不用Maven)

(1)创建项目

什么也不用选,直接next.

log4j2入门hello world

勾选从模板创建项目.

log4j2入门hello world

选好路径与填好项目名即可.

(2)添加jar包

log4j2入门hello world

选择刚才的lib目录,或者自己手动改成两个jar包(log4j-api-版本.jar,log4j-core-版本.jar).

log4j2入门hello world

(3)新建测试类

项目结构如下:

log4j2入门hello world

Main.java

package com.test;
import org.apache.logging.log4j.*;

public class Main {

    private static final Logger logger = LogManager.getLogger(Main.class.getName());
    public static void main(String[] args) {
        logger.info("info");
        logger.error("error");
        logger.debug("debug");
        logger.trace("trace");
        logger.fatal("fatel");
    }
}

(4)新建log4j2.xml

在src下新建log4j2.xml.

<?xml version="1.0" encoding="UTF-8"?>
<configuration status="OFF">
    <appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
        </Console>
    </appenders>
    <loggers>
        <logger name="com.test.Main" level="info" additivity="false">
            <appender-ref ref="Console"/>
        </logger>
        <root level="info">
            <appender-ref ref="Console"/>
        </root>
    </loggers>
</configuration>

(5)测试

直接点击run按钮.

log4j2入门hello world

6.IDEA下使用log4j2(带Maven)

(1)创建maven 项目模块

这里作者偷懒就直接在上面项目的基础上新建模块不新建项目了.

log4j2入门hello world

都不用选直接next.

log4j2入门hello world

填好GroupId与ArtifactId之后next.

log4j2入门hello world

最后选好位置.

(2)配置依赖

pom.xml中加入:

<dependencies>
    <dependency>
        <groupId>org.apache.logging.log4j</groupId>
        <artifactId>log4j-api</artifactId>
        <version>2.12.1</version>
    </dependency>
    <dependency>
        <groupId>org.apache.logging.log4j</groupId>
        <artifactId>log4j-core</artifactId>
        <version>2.12.1</version>
    </dependency>
</dependencies>

以下是完整的pom.xml文件

<?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">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>test</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-api</artifactId>
            <version>2.12.1</version>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>2.12.1</version>
        </dependency>
    </dependencies>

</project>

右键选择同步pom.xml.

log4j2入门hello world

选择右下角弹出的提示中的Import Changes.

log4j2入门hello world

(3)创建log4j2.xml

在target下的classes下创建log4j2.xml.

log4j2入门hello world

log4j2.xml:

<?xml version="1.0" encoding="UTF-8"?>
<configuration status="OFF">
    <appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
        </Console>
    </appenders>
    <loggers>
        <logger name="com.example.test" level="info" additivity="false">
            <appender-ref ref="Console"/>
        </logger>
        <root level="info">
            <appender-ref ref="Console"/>
        </root>
    </loggers>
</configuration>

(4)创建测试类

创建包与test.java.

test.java

package com.example;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
public class test {
    private static final Logger logger = LogManager.getLogger(test.class.getName());
    public static void main(String[] args) {
        logger.info("info");
        logger.error("error");
        logger.debug("debug");
        logger.trace("trace");
        logger.fatal("fatel");
    }
}