log4j2笔记 #02# 启用异步日志

索引

1. 参考
2. Making All Loggers Asynchronous
   • 第一步，添加相应的disruptor库
   • 第二步，设置系统属性log4j2.contextSelector
   • 第三步，检验！

参考

• Log4j2简介和异步日志梳理 - 简书

• Log4j – Log4j 2 Lock-free Asynchronous Loggers for Low-Latency Logging - Apache Log4j 2

• Log4j2与Slf4j的最佳实践 - 知乎

• Asynchronous Logging With Log4J Part 2 - DZone Performance

• java - log4j2: Location for setting Log4jContextSelector system property for asynchronous logging - Stack Overflow

Making All Loggers Asynchronous

将原本的log4j2同步日志转化为“完全异步日志模式”。官方文档：

This is simplest to configure and gives the best performance. To make all loggers asynchronous, add the disruptor jar to the classpath and set the system property log4j2.contextSelector to org.apache.logging.log4j.core.async.AsyncLoggerContextSelector.

Log4j-2.9 and higher require disruptor-3.3.4.jar or higher on the classpath. Prior to Log4j-2.9, disruptor-3.0.0.jar or higher was required.

第一步，添加相应的disruptor库

各个依赖包的版本需要对应。如下：

        <!-- https://mvnrepository.com/artifact/org.apache.logging.log4j/log4j-core -->
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>2.8.2</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.apache.logging.log4j/log4j-api -->
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-api</artifactId>
            <version>2.8.2</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.apache.logging.log4j/log4j-slf4j-impl -->
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-slf4j-impl</artifactId>
            <version>2.8.2</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.apache.logging.log4j/log4j-web -->
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-web</artifactId>
            <version>2.8.2</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/com.lmax/disruptor -->
        <!-- Asynchronous Loggers internally use the Disruptor, a lock-free
        inter-thread communication library, instead of queues, resulting in
        higher throughput and lower latency.-->
        <dependency>
            <groupId>com.lmax</groupId>
            <artifactId>disruptor</artifactId>
            <version>3.4.2</version>
        </dependency>

第二步，设置系统属性log4j2.contextSelector

一种简便的方式是在相应classpath下创建一个叫log4j2.component.properties的文件（maven项目直接放在main/resources就好），内容如下：

Log4jContextSelector=org.apache.logging.log4j.core.async.AsyncLoggerContextSelector

PS. Log4jContextSelector的第一个字母必须大写

第三步，检验！

首先你需要允许log4j2输出自身的debug信息，log4j2.xml：

<Configuration status="DEBUG">

然后启动你的web项目，在ide或者catalina.out里观察debug信息，类似下面这样就说明成功：