在 Spring Boot 3.5.3 中，要将默认的 Logback 替换为 Log4j2，需要以下步骤：

1. 添加 Log4j2 依赖

在 pom.xml中排除默认的 Logback 依赖并添加 Log4j2 依赖：

<dependencies><!-- 排除默认的 Logback --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter</artifactId><exclusions><exclusion><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-logging</artifactId></exclusion></exclusions></dependency><!-- 添加 Log4j2 Starter --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-log4j2</artifactId></dependency><!-- 可选：日志配置刷新支持 --><dependency><groupId>org.apache.logging.log4j</groupId><artifactId>log4j-liquibase</artifactId></dependency>
</dependencies>

2. 创建 Log4j2 配置文件

在 src/main/resources目录下创建 log4j2.xml文件：

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN" monitorInterval="30"><Appenders><!-- 控制台输出 --><Console name="Console" target="SYSTEM_OUT"><PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/></Console><!-- 文件输出 --><RollingFile name="File" fileName="logs/application.log"filePattern="logs/application-%d{yyyy-MM-dd}-%i.log"><PatternLayout><Pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n</Pattern></PatternLayout><Policies><!-- 每天滚动 --><TimeBasedTriggeringPolicy /><!-- 文件大小达到100MB时滚动 --><SizeBasedTriggeringPolicy size="100 MB"/></Policies><!-- 保留最近7天的日志 --><DefaultRolloverStrategy max="7"/></RollingFile><!-- 异步日志配置 --><Async name="Async" bufferSize="262144"><AppenderRef ref="File"/></Async></Appenders><Loggers><!-- Spring Boot 核心日志 --><Logger name="org.springframework" level="INFO"/><Logger name="org.apache" level="WARN"/><!-- Hibernate 日志 --><Logger name="org.hibernate.SQL" level="DEBUG" additivity="false"><AppenderRef ref="Console"/></Logger><Logger name="org.hibernate.type.descriptor.sql" level="TRACE" additivity="false"><AppenderRef ref="Console"/></Logger><!-- 自定义包日志级别 --><Logger name="com.myapp" level="DEBUG"/><!-- Root 日志设置 --><Root level="INFO"><AppenderRef ref="Console"/><AppenderRef ref="Async"/> <!-- 使用异步文件输出 --></Root></Loggers>
</Configuration>

3. 添加 application.yml 配置

在 application.yml中添加 Log4j2 相关配置：

spring:application:name: my-applicationlogging:config: classpath:log4j2.xmllevel:root: infoorg.springframework.web: debugcom.myapp.service: trace# 启用日志配置热更新log4j2:watch: trueshutdown-hook: disableshutdown-timeout: 30

4. 添加日志工具类

创建日志工具类以简化使用：

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;public class LogUtil {private LogUtil() {}public static Logger getLogger() {// 获取调用此方法的上层类名return LogManager.getLogger(Thread.currentThread().getStackTrace()[2].getClassName());}// 方法入参日志（使用MDC添加上下文信息）public static void logMethodEntry(Object... params) {Logger logger = getLogger();if(logger.isTraceEnabled()) {String methodName = Thread.currentThread().getStackTrace()[2].getMethodName();logger.trace("Entering: {} with params: {}", methodName, params);}}
}

5. 高级功能配置

5.1 日志脱敏配置

添加敏感信息脱敏配置类：

import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.core.pattern.ConverterKeys;
import org.apache.logging.log4j.core.pattern.LogEventPatternConverter;@Plugin(name = "SafeConverter", category = "Converter")
@ConverterKeys({"safe"})
public class SafeConverter extends LogEventPatternConverter {// 敏感信息正则匹配private static final String SENSITIVE_PATTERN = "\\b(?:password|passwd|pwd|secret|token|key|card|ccn|phone|tel|id)\\b[^=]*=\\s*['\"]?([^'\",\\s]+)";protected SafeConverter() {super("safe", "safe");}public static SafeConverter newInstance(String[] options) {return new SafeConverter();}@Overridepublic void format(LogEvent event, StringBuilder toAppendTo) {String message = event.getMessage().getFormattedMessage();toAppendTo.append(message.replaceAll(SENSITIVE_PATTERN, "$1=***"));}
}

在 log4j2.xml中使用：

<PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %safe{%msg}%n"/>

5.2 日志指标监控

添加 Log4j2 指标采集：

import io.micrometer.core.instrument.MeterRegistry;
import org.apache.logging.log4j.LogManager;
import org.springframework.context.annotation.Configuration;import javax.annotation.PostConstruct;@Configuration
public class LogMetricsConfig {private final MeterRegistry meterRegistry;public LogMetricsConfig(MeterRegistry meterRegistry) {this.meterRegistry = meterRegistry;}@PostConstructpublic void init() {// 采集ERROR级别的日志计数meterRegistry.gauge("log.error.count", LogManager.getRootLogger(), logger -> logger instanceof org.apache.logging.log4j.core.Logger ? ((org.apache.logging.log4j.core.Logger) logger).getCount().get() : 0);}
}

5.3 日志集中式管理

添加 Logstash 或 ELK 支持：

<!-- pom.xml 添加依赖 -->
<dependency><groupId>net.logstash.logback</groupId><artifactId>logstash-logback-encoder</artifactId><version>7.3</version>
</dependency>

配置 Logstash Appender：

<Appenders><!-- Logstash TCP 输出 --><LogstashTcpSocket name="Logstash" host="logstash.mycompany.com" port="5000"><JsonLayout compact="true" eventEol="true"><KeyValuePair key="appName" value="${spring:spring.application.name}"/><KeyValuePair key="environment" value="${spring:spring.profiles.active}"/></JsonLayout></LogstashTcpSocket>
</Appenders><Loggers><Root level="INFO"><AppenderRef ref="Logstash"/></Root>
</Loggers>

6. Spring Boot 配置类

添加日志相关的配置管理：

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.core.LoggerContext;
import org.springframework.boot.context.event.ApplicationStartedEvent;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.event.EventListener;import java.net.URI;@Configuration
public class LogConfig {/*** 应用启动后重新加载日志配置*/@EventListener(ApplicationStartedEvent.class)public void reloadLogConfig() {LoggerContext context = (LoggerContext) LogManager.getContext(false);context.setConfigLocation(URI.create("classpath:log4j2.xml"));context.reconfigure();}
}

7. 日志性能优化

7.1 异步日志配置优化

<!-- log4j2.xml -->
<AsyncLogger name="com.myapp" level="debug" additivity="false"><AppenderRef ref="Console"/><AppenderRef ref="File"/><!-- 队列大小 --><AsyncQueueSize>262144</AsyncQueueSize><!-- 等待策略 --><AsyncWaitStrategy type="Block"/>
</AsyncLogger>

7.2 日志开关控制器

import org.apache.logging.log4j.Level;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.core.LoggerContext;
import org.apache.logging.log4j.core.config.Configurator;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;@RestController
public class LogController {@GetMapping("/log/level")public String changeLogLevel(String logger, String level) {LoggerContext context = (LoggerContext) LogManager.getContext(false);// 设置特定日志级别if ("root".equalsIgnoreCase(logger)) {Configurator.setRootLevel(Level.valueOf(level));} else {Configurator.setLevel(logger, Level.valueOf(level));}context.reconfigure();return "Log level updated: " + logger + " -> " + level;}
}

8. 验证日志配置

创建测试控制器验证日志输出：

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;@RestController
public class LogTestController {private static final Logger logger = LogManager.getLogger(LogTestController.class);@GetMapping("/test/log")public String testLog() {logger.trace("This is a TRACE message");logger.debug("This is a DEBUG message");logger.info("This is an INFO message");logger.warn("This is a WARN message");logger.error("This is an ERROR message");return "Log messages generated!";}
}

访问 http://localhost:8080/test/log后，检查控制台和日志文件验证输出。

配置总结

此配置提供了：

1. 灵活的日志级别控制

2. 高性能的异步日志处理

3. 敏感信息保护

4. 监控和管理功能