日志JCL初探

1.新建module,jcl-demo

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">
    <parent>
        <artifactId>log-study</artifactId>
        <groupId>com.lxcourse</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>jcl-demo</artifactId>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <dependency>
            <groupId>commons-logging</groupId>
            <artifactId>commons-logging</artifactId>
            <version>1.2</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <encoding>UTF-8</encoding>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

2.JCLDemo.java默认使用JUL输出日志

package com.lxcourse.jcl;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.junit.Test;

public class JCLDemo {
    
    @Test
    public void testQuick(){
        Log log = LogFactory.getLog(JCLDemo.class);
        log.info("hello jcl");
    }
}

输出结果：

五月 29, 2020 8:22:36 上午 com.lxcourse.jcl.JCLDemo testQuick
信息: hello jcl

3.pom.xml中添加log4j的依赖

<dependency>
    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
    <version>1.2.17</version>
</dependency>

4.添加log4j.properties

log4j.rootLogger=trace,console

# 指定控制台日志输出的appender
log4j.appender.console = org.apache.log4j.ConsoleAppender
log4j.appender.console.layout = org.apache.log4j.PatternLayout
log4j.appender.console.layout.conversionPattern = [%-5p] %r %C %M %d{yyyy-MM-dd HH:mm:ss} %m%n

5.执行JCLDemo.testQuick()方法，查看输出

[INFO ] 0 com.lxcourse.jcl.JCLDemo testQuick 2020-05-29 08:29:57 hello jcl

6.JCL原理

1. 通过LogFactory动态加载Log实现类
2. 日志门面支持的日志实现数组

private static final String[] classesToDiscover = {
        LOGGING_IMPL_LOG4J_LOGGER,
        "org.apache.commons.logging.impl.Jdk14Logger",
        "org.apache.commons.logging.impl.Jdk13LumberjackLogger",
        "org.apache.commons.logging.impl.SimpleLog"
};

3. 获取具体的日志实现

for(int i=0; i<classesToDiscover.length && result == null; ++i) {
    result = createLogFromClass(classesToDiscover[i], logCategory, true);
}