SLF4J 日志绑定

https://www.bilibili.com/video/BV1iJ411H74S?p=23

SLF4J 支持各种日志框架。SLF4J 发行版附带了几个称为“SLF4J绑定”的 jar 文件，每个绑定对应一个受支持的框架。

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
1. 绑定已经实现了 SLF4J 的日志框架，直接添加对应依赖
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）

示例绑定 logback 日志实现

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">
    <modelVersion>4.0.0</modelVersion>

    <groupId>io.github.jihch</groupId>
    <artifactId>slf4j-demo</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>

    <dependencies>
        <!-- slf4j 日志门面 -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.27</version>
        </dependency>

        <!-- slf4j 内置的简单实现 -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>1.7.21</version>
        </dependency>

        <!-- logback 日志实现 -->
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.3</version>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>

</project>

SLF4JTest.java

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

public class SLF4JTest {

    public static final Logger LOGGER = LoggerFactory.getLogger(SLF4JTest.class);

    @Test
    public void test() {
        // 日志输出
        LOGGER.error("error");
        LOGGER.warn("warn");
        LOGGER.info("info");
        LOGGER.debug("debug");
        LOGGER.trace("trace");

        // 使用占位符输出日志信息
        String name = "jihch";
        Integer age = 14;
        LOGGER.info("用户：{}，{}", name, age);

        // 将系统的异常信息输出
        try {
            int i = 1/0;
        } catch (Exception e) {
//            e.printStackTrace();
            LOGGER.error("出现异常：", e);
        }

    }

}

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/I:/maven_repository/org/slf4j/slf4j-simple/1.7.21/slf4j-simple-1.7.21.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/I:/maven_repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.slf4j.impl.SimpleLoggerFactory]
[main] ERROR io.github.jihch.SLF4JTest - error
[main] WARN io.github.jihch.SLF4JTest - warn
[main] INFO io.github.jihch.SLF4JTest - info
[main] INFO io.github.jihch.SLF4JTest - 用户：jihch，14
[main] ERROR io.github.jihch.SLF4JTest - 出现异常：
java.lang.ArithmeticException: / by zero
	at io.github.jihch.SLF4JTest.test(SLF4JTest.java:27)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)
	at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)

Process finished with exit code 0

在 pom.xml 加入了对 logback 的依赖：

        <!-- logback 日志实现 -->
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.3</version>
        </dependency>

只需要引入 logback-classic，因为依赖传递，就不需要再添加对 logback-core 的依赖

观察控制台可以发现信息提示：

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/I:/maven_repository/org/slf4j/slf4j-simple/1.7.21/slf4j-simple-1.7.21.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/I:/maven_repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.slf4j.impl.SimpleLoggerFactory]

类路径包含多个 SLF4J 绑定，有 slf4j-simple，还有 logback-classic，实际绑定 SimpleLoggerFactory，要测试 logback，所以先注释掉 pom.xml 中对 slf4j-simple 的引入；

    <dependencies>
        <!-- slf4j 日志门面 -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.27</version>
        </dependency>

        <!-- slf4j 内置的简单实现 -->
<!--        <dependency>-->
<!--            <groupId>org.slf4j</groupId>-->
<!--            <artifactId>slf4j-simple</artifactId>-->
<!--            <version>1.7.21</version>-->
<!--        </dependency>-->

        <!-- logback 日志实现 -->
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.3</version>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>

再次运行

19:24:56.617 [main] ERROR io.github.jihch.SLF4JTest - error
19:24:56.619 [main] WARN io.github.jihch.SLF4JTest - warn
19:24:56.619 [main] INFO io.github.jihch.SLF4JTest - info
19:24:56.619 [main] DEBUG io.github.jihch.SLF4JTest - debug
19:24:56.619 [main] INFO io.github.jihch.SLF4JTest - 用户：jihch，14
19:24:56.626 [main] ERROR io.github.jihch.SLF4JTest - 出现异常：
java.lang.ArithmeticException: / by zero
	at io.github.jihch.SLF4JTest.test(SLF4JTest.java:27)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)
	at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)

Process finished with exit code 0

SLF4J 日志绑定

示例绑定 logback 日志实现

pom.xml

SLF4JTest.java

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SLF4J 日志绑定

示例 绑定 logback 日志实现

pom.xml

SLF4JTest.java

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示例绑定 logback 日志实现