1 日志框架方案
2 AsyncLogger配置异步日志
3 相关问题
- 3.1 log4j2和logback冲突问题
- 3.2 spring boot使用log4j2
参考文献

本文概览：选择打印日志方案为：使用log4j，并且使用AsyncLogger异步打印。

1 日志框架方案

1、项目中选择日志框架是log4j2。

目前常遇见的日志框架有log4j、logback、log4j2，logback是为了优化log4j而生的，log4j2又在logback基础上做了优化。所以日志框架选型顺序为：log4j2 > logback > log4j。这三个都是同一个作者所写，都实现字sl4j的接口，sl4j全称Simple logging Facade for Java。

2、log4j2使用AsyncLogger的异步方式

使用同步方式，在高并发情况下会对接口性能有影响，所以使用异步方式，通过异步方式可以将记录日志的I/O操作独立成一个线程来执行。log4j2的异步日志有AsyncAppender和AsyncLogger两种方式，建议使用AsyncLogger方式。AsyncLogger是log4j2新增的功能，使用LMAX Disruptor来实现高吞吐量；Async Appender在log4j1的时候就已经有了。log4j2的AsyncLogger具有高吞吐量和低延迟的特性

（1）吞吐量对比

（2）低延迟(Low-Latency)对比

2 AsyncLogger配置异步日志

1、maven配置

<!--配置4j-->
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-api</artifactId>
            <version>2.3</version>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>2.3</version>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-slf4j-impl</artifactId>
            <version>2.3</version>
        </dependency>
        <dependency>
            <groupId>com.lmax</groupId>
            <artifactId>disruptor</artifactId>
            <version>3.4.2</version>
        </dependency>

<groupId>org.apache.logging.log4j</groupId>

</dependency>

<groupId>org.apache.logging.log4j</groupId>

</dependency>

<groupId>org.apache.logging.log4j</groupId>

</dependency>

<artifactId>disruptor</artifactId>

</dependency>

2、log4j2.xml配置

<?xml version="1.0" encoding="UTF-8"?>

<!-- No need to set system property "Log4jContextSelector" to any value
     when using <asyncLogger> or <asyncRoot>. -->

<Configuration status="WARN">

    <Appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout>
                <Pattern>%d %p %class{1.} [%t] %location %m %ex%n</Pattern>
            </PatternLayout>
        </Console>
        <!-- Async Loggers will auto-flush in batches, so switch off immediateFlush. -->
        <RandomAccessFile name="RandomAccessFile" fileName="./sync.log"
                          immediateFlush="false" append="false">
            <PatternLayout>
                <Pattern>%d %p %class{1.} [%t] %location %m %ex%n</Pattern>
            </PatternLayout>
        </RandomAccessFile>
    </Appenders>
    <Loggers>
        <!-- pattern layout actually uses location, so we need to include it -->
        <AsyncLogger name="com.test" level="info" includeLocation="true" additivity="false">
            <AppenderRef ref="RandomAccessFile"/>
            <AppenderRef ref="Console"/>
        </AsyncLogger>
        <AsyncRoot level="info" includeLocation="true">
            <AppenderRef ref="RandomAccessFile"/>
        </AsyncRoot>
    </Loggers>
</Configuration>

<?xml version="1.0" encoding="UTF-8"?>

<!-- No need to set system property "Log4jContextSelector" to any value

when using <asyncLogger> or <asyncRoot>. -->

<Pattern>%d %p %class{1.} [%t] %location %m %ex%n</Pattern>

</PatternLayout>

</Console>

<RandomAccessFile name="RandomAccessFile" fileName="./sync.log"

immediateFlush="false" append="false">

<Pattern>%d %p %class{1.} [%t] %location %m %ex%n</Pattern>

</PatternLayout>

</RandomAccessFile>

</Appenders>

</AsyncLogger>

</AsyncRoot>

</Loggers>

</Configuration>

3 相关问题

3.1 log4j2和logback冲突问题

一个项目中只能使用log4j2或者logback。假设在项目中使用了log4j2，此时使用外部依赖jar时候，发现外部依赖使用了logbakc，如何解决这个问题？将外部依赖的logback的包通过exclude排除掉。

3.2 spring boot使用log4j2

spring boot默认使用logback，通过如下maven配置来使用log4j2：

<!-- Spring boot默认使用logback -->
<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter</artifactId>
	<exclusions>
		<exclusion>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-logging</artifactId>
		</exclusion>
	</exclusions>
</dependency>

<!-- 添加log4j2 -->
<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-log4j2</artifactId>
</dependency>

<!-- log4j2使用AsyncLogger异步 -->
<dependency>
  <groupId>com.lmax</groupId>
  <artifactId>disruptor</artifactId>
  <version>3.3.6</version>
</dependency>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter</artifactId>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-logging</artifactId>

</exclusion>

</exclusions>

</dependency>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-log4j2</artifactId>

</dependency>

<artifactId>disruptor</artifactId>

</dependency>

如果报错“but there’s no log4j-web module available”，则添加如下：

<dependency>
      <groupId>org.apache.logging.log4j</groupId>
       <artifactId>log4j-web</artifactId>
       <version>2.10.0</version>
</dependency>