【日常记录-Java】应用引入Slf4J

1. 简介

SLF4J(Simple Logging Facade for Java) 是Java的一个简单日志门面，为Java日志访问提供了一套标准、规范的API框架。而具体日志的实现则可以根据这套接口去实现具体的日志框架，以便将来需要更换日志框架时，只替换实现框架即可。常见的具体实现有JUL、log4j、logback、log4j2等。

2. 操作

2.1 引入依赖

<dependency><groupId>org.slf4j</groupId><artifactId>slf4j-api</artifactId><version>2.0.16</version>
</dependency>
<dependency><groupId>ch.qos.logback</groupId><artifactId>logback-classic</artifactId><version>1.5.8</version>
</dependency>

2.2 配置日志实现

对于Logback，通常在类路径下（如src/main/resources目录）创建一个名为logback-config.xml配置文件，在其中定义日志记录级别、格式、输出目的地等。

<?xml version="1.0" encoding="UTF-8"?>  
<configuration scan="true" scanPeriod="60 seconds" debug="false">  <!-- 工程名/项目名 -->  <contextName>project_name</contextName>  <!-- 把>=debug的日志输出到控制台 -->  <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">  <encoder>  <pattern>%-4relative %date{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{35} - %msg %n</pattern>  <charset>UTF-8</charset></encoder>  </appender>  <!-- 系统日志输出到文件，并设置滚动策略 -->  <appender name="INFO_FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">  <file>logs/info.log</file>  <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">  <fileNamePattern>logs/info.%d{yyyy-MM-dd}.log</fileNamePattern>  <maxHistory>30</maxHistory>  </rollingPolicy>  <encoder>  <pattern>%-4relative %date{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{35} - %msg%n</pattern>  <charset>UTF-8</charset></encoder>  <filter class="ch.qos.logback.classic.filter.LevelFilter"><level>ERROR</level><onMatch>DENY</onMatch><onMismatch>ACCEPT</onMismatch></filter></appender>  <!-- 错误日志输出到文件，并设置滚动策略 -->  <appender name="ERROR_FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">  <file>logs/error.log</file>  <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">  <fileNamePattern>logs/error.%d{yyyy-MM-dd}.log</fileNamePattern>  <maxHistory>30</maxHistory>  </rollingPolicy>  <encoder>  <pattern>%-4relative %date{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{35} - %msg%n</pattern>  <charset>UTF-8</charset></encoder>  <filter class="ch.qos.logback.classic.filter.LevelFilter">  <level>ERROR</level>  <onMatch>ACCEPT</onMatch>  <onMismatch>DENY</onMismatch>  </filter>  </appender>  <!-- 根日志级别控制，并引用所有appender -->  <root level="INFO">  <appender-ref ref="STDOUT"/>  <appender-ref ref="INFO_FILE"/>  <appender-ref ref="ERROR_FILE"/>  </root>  
</configuration>

2.3 启用配置并使用

import ch.qos.logback.classic.LoggerContext;
import ch.qos.logback.classic.joran.JoranConfigurator;
import ch.qos.logback.core.joran.spi.JoranException;
import ch.qos.logback.core.util.StatusPrinter2;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;import java.io.InputStream;public class Main {public static void main(String[] args){// step1: 使用配置文件完成配置LoggerContext context = (LoggerContext) LoggerFactory.getILoggerFactory();try {InputStream configStream = Main.class.getClassLoader().getResourceAsStream("logback-config.xml");if (configStream == null) {throw new RuntimeException("Could not find logback-config.xml");}JoranConfigurator configurator = new JoranConfigurator();configurator.setContext(context);context.reset();configurator.doConfigure(configStream);new StatusPrinter2().printInCaseOfErrorsOrWarnings(context);} catch (JoranException je) {throw new RuntimeException(je);}// step2: 进行日志记录Logger log = LoggerFactory.getLogger(Main.class);log.info("this is a logger!");}
}