Log4j2基本使用

Log4j2简介

log4j2是log4j 1.x 的升级版,2015年5月,Apache宣布log4j1.x 停止更新.最新版为1.2.17.

log4j2参考了logback的一些优秀的设计,并且修复了一些问题,因此带来了一些重大的提升,主要有：

1、异常处理：在logback中,Appender中的异常不会被应用感知到,但是在log4j2中,提供了一些异常处理机制.

2、性能提升：log4j2相较于log4j 1和logback都具有很明显的性能提升.

3、自动重载配置：参考了logback的设计,提供自动刷新参数配置,可以动态的修改日志的级别而不需要重启应用.

4、无垃圾机制,log4j2在大部分情况下,都可以使用其设计的一套无垃圾机制,避免频繁的日志收集导致的jvm gc.

1.Jar包依赖

直接依赖

在Maven的父工程pom.xml添加如下依赖：

<dependencyManagement>
    <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>
</dependencyManagement>

使用bom管理依赖

<dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>org.apache.logging.log4j</groupId>
      <artifactId>log4j-bom</artifactId>
      <version>2.12.1</version>
      <scope>import</scope>
      <type>pom</type>
    </dependency>
  </dependencies>
</dependencyManagement>

然后在使用Log4j2的子工程pom.xml添加如下依赖,
This eliminates the need to write a specific version number,
Make sure that the subprojects of the project all use the same versionLog4j2.

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

在复杂场景下,May not only rely on the above twojar包,
这种方法可以保证Log4j2Versions are consistent between modules.

2.测试代码

为了演示Log4j2的功能,Create the following test class：

package org.apache.logging.log4j;

public class Log4j2Test {
    
    private static Logger LOG = LogManager.getLogger(Log4j2Test.class);

    public static void main(String[] args) throws Exception {
    
        // The log keeps printing,用于测试Log4j2功能
        while (true) {
    
            logAll();
        }
    }

    // Print logs at various levels for testing
    public static void logAll() throws Exception {
    
        LOG.trace("trace level log");
        LOG.debug("debug level log");
        LOG.info("info level log");
        LOG.error("error level log");
        LOG.fatal("fatal level log");
        // 设置休眠时间(单位ms),控制日志打印速度
        Thread.sleep(3);
    }
}

3.打印日志

运行上面的测试程序,
The following log is printed on the console：

ERROR StatusLogger No Log4j 2 configuration file found. Using default configuration (logging only errors to the console), or user programmatically provided configurations. Set system property 'log4j2.debug' to show Log4j 2 internal initialization logging. See https://logging.apache.org/log4j/2.x/manual/configuration.html for instructions on how to configure Log4j 2
11:33:08.438 [main] ERROR org.apache.logging.log4j.Log4j2Test - error level log
11:33:08.440 [main] FATAL org.apache.logging.log4j.Log4j2Test - fatal level log

可以看到ERROR报错了,没有找到Log4j2的配置文件,
使用了默认配置,只打印errorlevel log toconsole控制台,
Then the console outputerror和fatalTwo levels of log information.

4.日志级别

Log4j2共有8种日志级别,
Sort by priority from smallest to largest:

ALL < TRACE < DEBUG < INFO < WARN < ERROR < FATAL < OFF