Slf4j初探

1.新建module,slf4j-demo

2.pom.xml添加依赖

<?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>sfl4j-demo</artifactId>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.28</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>1.7.28</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>

3.编写测试类Slf4jDemo.java

package com.lxcourse.slf4j;

import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * @author doubledumbao
 * Slf4j快速入门
 */
public class Slf4jDemo {

    public static final Logger LOGGER = LoggerFactory.getLogger(Slf4jDemo.class);

    @Test
    public  void testQuick(){
        LOGGER.error("error");
        LOGGER.warn("warn");
        LOGGER.info("info");
        LOGGER.debug("debug");
        LOGGER.trace("trace");
        String name = "lxcourse";
        String url = "https://www.lxcourse.cn";
        LOGGER.info("网站:{}，网址:{}",name,url);

        try {
            int a = 10/0;
        } catch (Exception e) {
            LOGGER.error("发生异常{}","hello",e);
        }
    }

}

slf4j绑定日志框架

4.slf4j绑定logback

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>sfl4j-demo</artifactId>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.28</version>
        </dependency>
        <!--
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>1.7.28</version>
        </dependency>
        -->
        <!--   logback日志     -->
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.3</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>

5.slf4j绑定slf4j-nop

<?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>sfl4j-demo</artifactId>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.28</version>
        </dependency>
        <!-- slf4j 内置简单日志
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>1.7.27</version>
        </dependency>
        -->
        <!--   logback日志
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.3</version>
        </dependency>
        -->
        <!-- 绑定为NOP，静默丢弃所有日志记录。       -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-nop</artifactId>
            <version>1.7.28</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>

6.slf4j绑定log4j

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>sfl4j-demo</artifactId>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.28</version>
        </dependency>
        <!-- slf4j 内置简单日志
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>1.7.27</version>
        </dependency>
        -->
        <!--   logback日志
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.3</version>
        </dependency>
        -->
        <!-- 绑定为NOP，静默丢弃所有日志记录。
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-nop</artifactId>
            <version>1.7.28</version>
        </dependency>
         -->
        <!--  绑定log4j 1.2版（一种广泛使用的日志记录框架）。您还需要将log4j.jar放在类路径上。      -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.7.28</version>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</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>

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

7.slf4j绑定jdk14

<?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>sfl4j-demo</artifactId>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.28</version>
        </dependency>
        <!-- slf4j 内置简单日志
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>1.7.27</version>
        </dependency>
        -->
        <!--   logback日志
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.3</version>
        </dependency>
        -->
        <!-- 绑定为NOP，静默丢弃所有日志记录。
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-nop</artifactId>
            <version>1.7.28</version>
        </dependency>
         -->
        <!--  绑定log4j 1.2版（一种广泛使用的日志记录框架）。您还需要将log4j.jar放在类路径上。
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.7.28</version>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
         -->
        <!-- 绑定JUL日志 -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-jdk14</artifactId>
            <version>1.7.28</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>

8.使用slf4j的日志绑定流程:

添加slf4j-api的依赖
使用slf4j的API在项目中进行统一的日志记录
绑定具体的日志实现框架

3.1 绑定已经实现了slf4j的日志框架,直接添加对应依赖

3.2 绑定没有实现slf4j的日志框架,先添加日志的适配器,再添加实现类的依赖
slf4j有且仅有一个日志实现框架的绑定(如果出现多个默认使用第一个依赖日志实现)

9.slf4j桥接器

比如原来项目中使用的log4j，依赖如下：

<?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>slf4j-bridge-demo</artifactId>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</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>

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

测试代码：

package com.lxcourse.log4j;

import org.apache.log4j.Logger;
import org.junit.Test;

/**
 * @author doubledumbao
 */
public class Log4jDemo {

    public static Logger LOGGER = Logger.getLogger(Log4jDemo.class);

    @Test
    public void testQuick(){
        LOGGER.error("error");
        LOGGER.warn("warn");
        LOGGER.info("info");
        LOGGER.debug("debug");
        LOGGER.trace("trace");
    }
}

现在将日志框架替换为slf4j+logback

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>slf4j-bridge-demo</artifactId>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <!-- 注释掉log4j的依赖
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        -->
        <!--  slf4j的依赖  -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.28</version>
        </dependency>
        <!--  logback的依赖      -->
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.3</version>
        </dependency>
        <!--   log4j桥接器     -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>log4j-over-slf4j</artifactId>
            <version>1.7.28</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>

注意问题:

jcl-over-slf4j.jar和 slf4j-jcl.jar不能同时部署。前一个jar文件将导致JCL将日志系统的选择委托给 SLF4J，后一个jar文件将导致SLF4J将日志系统的选择委托给JCL，从而导致无限循环。
log4j-over-slf4j.jar和slf4j-log4j12.jar不能同时出现
jul-to-slf4j.jar和slf4j-jdk14.jar不能同时出现
所有的桥接都只对Logger日志记录器对象有效，如果程序中调用了内部的配置类或者是Appender,Filter等对象，将无法产生效果。

10.SLF4J原理解析

SLF4J通过LoggerFactory加载日志具体的实现对象。
LoggerFactory在初始化的过程中，会通过performInitialization()方法绑定具体的日志实现。
在绑定具体实现的时候，通过类加载器，加载org/slf4j/impl/StaticLoggerBinder.class
所以，只要是一个日志实现框架，在org.slf4j.impl包中提供一个自己的StaticLoggerBinder类，在其中提供具体日志实现的LoggerFactory就可以被SLF4J所加载

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原文地址：https://www.cnblogs.com/zhaoran8775/p/12990755.html