// 使用log4j，需要log4j.jar 
import org.apache.log4j.Logger; 
Logger logger_log4j = Logger.getLogger(Test.class); 
logger_log4j.info("Hello World!"); 

// 使用log4j2，需要log4j-api.jar、log4j-core.jar 
import org.apache.logging.log4j.LogManager; 
import org.apache.logging.log4j.Logger; 
Logger logger_log4j2 = LogManager.getLogger(Test.class); 
logger_log4j2.info("Hello World!"); 

// logback，需要logback-classic.jar、logback-core.jar 
import ch.qos.logback.classic.Logger; 
import ch.qos.logback.classic.LoggerContext; 
Logger logger_logback = new LoggerContext().getLogger(Test.class); logger_logback.info("Hello World!");

import org.slf4j.Logger; 
import org.slf4j.LoggerFactory; 
Logger logger = LoggerFactory.getLogger(Test.class); 
logger.info("Hello World!")

<!-- Maven 依賴配置 -->
<dependencies>
    <!-- SLF4J API -->
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
        <version>2.0.9</version>
    </dependency>
    <!-- Logback Classic 實(shí)現(xiàn) -->
    <dependency>
        <groupId>ch.qos.logback</groupId>
        <artifactId>logback-classic</artifactId>
        <version>1.4.11</version>
    </dependency>
</dependencies>

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class ExampleService {
    // 獲取Logger實(shí)例
    private static final Logger logger = LoggerFactory.getLogger(ExampleService.class);
    
    public void processUser(String userId) {
        logger.debug("Processing user: {}", userId); // 使用占位符，避免字符串拼接
        logger.info("User processing started");
        
        try {
            // 業(yè)務(wù)邏輯
            logger.info("User {} processed successfully", userId);
        } catch (Exception e) {
            logger.error("Failed to process user: " + userId, e); // 記錄異常信息
        }
    }
}

<?xml versinotallow="1.0" encoding="UTF-8"?>
<configuration scan="true" scanPeriod="30 seconds">
    
    <!-- 定義變量 -->
    <property name="LOG_HOME" value="./logs"/>
    <property name="APP_NAME" value="myapp"/>
    
    <!-- 開發(fā)環(huán)境開關(guān) -->
    <springProfile name="dev">
        <property name="LOG_LEVEL" value="DEBUG"/>
    </springProfile>
    <springProfile name="prod">
        <property name="LOG_LEVEL" value="INFO"/>
    </springProfile>
    
    <!-- 控制臺(tái)輸出 -->
    <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %level %logger{36} - %msg%n</pattern>
        </encoder>
    </appender>
    
    <!-- 更多Appender配置 -->
    
    <!-- 根日志器 -->
    <root level="${LOG_LEVEL:-INFO}">
        <appender-ref ref="CONSOLE"/>
    </root>
    
    <!-- 特定包的日志級(jí)別 -->
    <logger name="com.example.service" level="DEBUG"/>
</configuration>

<appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
    <encoder>
        <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
    </encoder>
    <!-- 過濾器：只輸出INFO及以上級(jí)別 -->
    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
        <level>INFO</level>
    </filter>
</appender>

<!-- 滾動(dòng)文件輸出（按天） -->
<appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <file>${LOG_HOME}/${APP_NAME}.log</file>
    <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
        <!-- 每天生成一個(gè)文件 -->
        <fileNamePattern>${LOG_HOME}/archive/%d{yyyy-MM-dd}/${APP_NAME}.%i.log.gz</fileNamePattern>
        <!-- 保留30天 -->
        <maxHistory>30</maxHistory>
        <!-- 單個(gè)文件最大100MB -->
        <timeBasedFileNamingAndTriggeringPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP">
            <maxFileSize>100MB</maxFileSize>
        </timeBasedFileNamingAndTriggeringPolicy>
    </rollingPolicy>
    <encoder>
        <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
    </encoder>
</appender>

<!-- 根日志器設(shè)置 -->
<root level="${LOG_LEVEL:-INFO}">
    <appender-ref ref="CONSOLE"/>
    <appender-ref ref="FILE"/>
</root>

<!-- 特定包/類級(jí)別設(shè)置 -->
<!-- 特定日志器：將 com.example.service 包的日志級(jí)別設(shè)為 DEBUG，且日志僅輸出到文件，不傳遞給根日志器（避免控制臺(tái)重復(fù)輸出） -->
<logger name="com.example.service" level="DEBUG" additivity="false">
    <appender-ref ref="FILE" />
</logger>

<!-- 特定日志器：將 org.springframework 包的日志級(jí)別設(shè)為 WARN，減少不必要的日志輸出 -->
<logger name="org.springframework" level="WARN" />

// 在代碼中使用MDC
import org.slf4j.MDC;

public class UserService {
    public void processUserRequest(String userId, String requestId) {
        // 將上下文信息放入MDC
        MDC.put("userId", userId);
        MDC.put("requestId", requestId);
        
        logger.info("Processing user request"); // 自動(dòng)包含MDC信息
        
        // 業(yè)務(wù)處理...
        
        // 清理MDC
        MDC.clear();
    }
}

<pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] [%X{userId}] [%X{requestId}] %-5level %logger{36} - %msg%n</pattern>

<!-- 異步日志（提升性能） -->
<appender name="ASYNC_FILE" class="ch.qos.logback.classic.AsyncAppender">
    <appender-ref ref="FILE"/>
    <!-- 隊(duì)列大小 -->
    <queueSize>256</queueSize>
    <!-- 丟棄級(jí)別低于ERROR的日志（可選） -->
    <discardingThreshold>0</discardingThreshold>
</appender>

<!-- 開發(fā)環(huán)境配置 -->
<springProfile name="dev">
    <root level="DEBUG">
        <appender-ref ref="CONSOLE"/>
    </root>
</springProfile>

<!-- 生產(chǎn)環(huán)境配置 -->
<springProfile name="prod">
    <root level="INFO">
        <appender-ref ref="ASYNC_FILE"/>
    </root>
</springProfile>

<appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <!-- 只記錄ERROR級(jí)別日志 -->
    <filter class="ch.qos.logback.classic.filter.LevelFilter">
        <level>ERROR</level>
        <onMatch>ACCEPT</onMatch>
        <onMismatch>DENY</onMismatch>
    </filter>
</appender>