logback日志自定义占位符

前言

在大型系统运维中，很大程度上是需要依赖日志的。在java大型web工程中，一般都会使用slf4j+logback这一个组合来实现日志的管理。

logback中很多现成的占位符可以可以直接使用，比如线程号【%t】、时间【%d】、日志等级【%p】，更多详细的占位符可以参考后文的占位符总结。

实际应用中，仅仅使用这些已经存在的占位符可能不够，比如我想给我的日志加一个traceId，通过这个traceId我可以快速的定位到我这个请求的所有日志，方便日志追踪。

针对日志中自定义占位符，logback提供了两种解决方案。下面分别来介绍一下

自定义traceId占位符

使用MDC

mdc的全称是Mapped Diagnostic Context，是Logback日志框架中的一个功能，它允许你在同一个线程的执行路径上设置一系列的上下文信息（即键值对），这些上下文信息可以自动地添加到日志输出中

logback.xml配置

<?xml version="1.0" encoding="UTF-8"?>
<configuration scan="true" scanPeriod="60 seconds" debug="false"><contextName>${APP_NAME}</contextName><property name="APP_NAME" value="MouseDemo"/><property name="LOG_PATH" value="./system_log/MouseDemo"/><property name="CONSOLE_LOG_PATTERN"value="%d | %X{traceId}| %highlight(%-5level) | %boldYellow(%thread) | %boldGreen(%logger) | %msg%n"/><!--输出到控制台--><appender name="console" class="ch.qos.logback.core.ConsoleAppender"><encoder><pattern>${CONSOLE_LOG_PATTERN}</pattern><charset>UTF-8</charset></encoder></appender><root level="info"><appender-ref ref="console"/></root></configuration>

在logback中，自定义的占位符是通过%X{配置的键}来获取的

设置MDC

在web工程中，设置traceId的时机很重要，一般是放在拦截器中。

自定义一个拦截器

package com.tml.mouseDemo.config;import cn.hutool.core.lang.UUID;
import lombok.extern.slf4j.Slf4j;
import org.slf4j.MDC;
import org.springframework.web.servlet.HandlerInterceptor;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import static com.tml.mouseDemo.constants.CommonConstants.TRACE_ID;@Slf4j
public class TraceInterceptor implements HandlerInterceptor {@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {String traceId = UUID.fastUUID().toString(true);log.info("TraceInterceptor preHandle,generate traceId is:{}", traceId);MDC.put(TRACE_ID, traceId);return true;}@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {log.info("TraceInterceptor afterCompletion,ready to clean traceId:{}", MDC.get(TRACE_ID));MDC.remove(TRACE_ID);}
}

注册拦截器

package com.tml.mouseDemo.config;import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;import java.nio.charset.Charset;
import java.util.List;@Configuration
public class WebAppConfig implements WebMvcConfigurer {@Beanpublic HttpMessageConverter<String> responseBodyConverter() {StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter(Charset.forName("UTF-8"));return stringHttpMessageConverter;}@Overridepublic void configureMessageConverters(List<HttpMessageConverter<?>> converters) {converters.add(responseBodyConverter());}@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(new TraceInterceptor()).addPathPatterns("/**");registry.addInterceptor(new RequestInterceptor()).addPathPatterns("/**");}
}

 

演示案例

经过上面两步的配置，日志上就会额外多一个traceId了

先定义一个service类

package com.tml.mouseDemo.service;import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Service;@Service
@Slf4j
public class TraceService {public void trace(String type) throws InterruptedException {log.info("trace start,type:{}", type);Thread.sleep(1000L);log.info("trace end");}
}

 

定义一个restful接口

package com.tml.mouseDemo.controller;import com.tml.mouseDemo.constants.CommonResponse;
import com.tml.mouseDemo.service.TraceService;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RestController;import java.util.concurrent.Executor;
import java.util.concurrent.ThreadPoolExecutor;@RestController
@Slf4j
public class TraceController {@Autowiredprivate TraceService traceService;@PostMapping("/trace")public CommonResponse<String> trace(String type) throws InterruptedException {log.info("trace type:{}", type);traceService.trace(type);return CommonResponse.success("success");}}

这里的案例是单线程，看下运行结果

 日志中，确实是多了一个traceId，符合预期

不过MDC有其局限性，仅支持单线程的数据传递。因为其底层是基于ThreadLocal来实现的，如下图

 

 局限性

下面来看一下再多线程环境下，使用MDC会有什么样的效果

package com.tml.mouseDemo.controller;import com.tml.mouseDemo.constants.CommonResponse;
import com.tml.mouseDemo.service.TraceService;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RestController;import java.util.concurrent.Executor;
import java.util.concurrent.ThreadPoolExecutor;@RestController
@Slf4j
public class TraceController {@Autowiredprivate ThreadPoolExecutor executor;@Autowiredprivate Executor ttlExecutor;@Autowiredprivate TraceService traceService;@PostMapping("/traceWithThread")public CommonResponse<String> traceWithThread(String type) throws InterruptedException {log.info("traceWithThread type:{}", type);traceService.trace(type);//模拟异步发短信new Thread(() -> {try {Thread.sleep(2000);String sendMsg = "hello world";log.info("sendMsg:{}", sendMsg);} catch (Exception e) {log.error("traceWithThread occur error", e);}}, "trace--001").start();return CommonResponse.success("success");}}

这里通过在主线程中new一个子线程来模拟多线程，运行一下看下结果

从图中可以看出，子线程的日志中是没有输出traceId的，这个就是MDC的局限性。看过前文阿里巴巴TransmittableThreadLocal使用指南的朋友们应该知道，这种new出来的线程不支持，那么使用线程池也肯定是不支持数据传递。

 

使用自定义Converter

相比MDC，使用自定义的Converter就会显得更加的灵活了，看下使用自定义的Converter的使用流程

定义traceId的存取

package com.tml.mouseDemo.config;import com.alibaba.ttl.TransmittableThreadLocal;public class TraceContext {private static final ThreadLocal<String> TRACE_CONTEXT = new TransmittableThreadLocal<>();public static String get() {return TRACE_CONTEXT.get();}public static void set(String age) {TRACE_CONTEXT.set(age);}public static void clean() {if (TRACE_CONTEXT.get() != null) {TRACE_CONTEXT.remove();}}
}

MDC使用的是ThreadLocalL来存储，我们这里自定义采用阿里巴巴的TransmittableThreadLocal，为什么要使用这个，详细的可以参考这篇博文阿里巴巴TransmittableThreadLocal使用指南 

定义Converter

package com.tml.mouseDemo.core.log;import ch.qos.logback.classic.pattern.ClassicConverter;
import ch.qos.logback.classic.spi.ILoggingEvent;
import com.tml.mouseDemo.config.TraceContext;import java.util.Optional;public class TraceIdConverter extends ClassicConverter {@Overridepublic String convert(ILoggingEvent iLoggingEvent) {return Optional.ofNullable(TraceContext.get()).orElse("");}
}

拦截器调整

package com.tml.mouseDemo.config;import cn.hutool.core.lang.UUID;
import lombok.extern.slf4j.Slf4j;
import org.springframework.web.servlet.HandlerInterceptor;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;@Slf4j
public class TraceInterceptor implements HandlerInterceptor {@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {String traceId = UUID.fastUUID().toString(true);log.info("TraceInterceptor preHandle,generate traceId is:{}", traceId);TraceContext.set(traceId);return true;}@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {log.info("TraceInterceptor afterCompletion,ready to clean traceId:{}", TraceContext.get());TraceContext.clean();}
}

改成从TraceContext中获取traceId，拦截器的注册和上文的保持一致。 

 

注册Converter

 <conversionRule conversionWord="traceId" converterClass="com.tml.mouseDemo.core.log.TraceIdConverter"/>

logback.xml配置

<?xml version="1.0" encoding="UTF-8"?>
<configuration scan="true" scanPeriod="60 seconds" debug="false"><conversionRule conversionWord="traceId" converterClass="com.tml.mouseDemo.core.log.TraceIdConverter"/><contextName>${APP_NAME}</contextName><property name="APP_NAME" value="MouseDemo"/><property name="LOG_PATH" value="./system_log/MouseDemo"/><property name="CONSOLE_LOG_PATTERN"value="%d | %traceId| %highlight(%-5level) | %boldYellow(%thread) | %boldGreen(%logger) | %msg%n"/><!--输出到控制台--><appender name="console" class="ch.qos.logback.core.ConsoleAppender"><encoder><pattern>${CONSOLE_LOG_PATTERN}</pattern><charset>UTF-8</charset></encoder></appender><root level="info"><appender-ref ref="console"/></root></configuration>

这里直接使用注册的Converter的traceId来作为占位符，而不是使用%X{键}来获取traceId

演示案例

直接new线程

代码案例和MDC中使用new创建线程一样，直接看下运行结果

子线程的日志中有traceId，并且是和父线程的traceId保持一致，达到预期

使用线程池

为了达到演示效果，我这里定义了两个线程池

package com.tml.mouseDemo.config;import com.alibaba.ttl.threadpool.TtlExecutors;
import com.google.common.util.concurrent.ThreadFactoryBuilder;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import lombok.extern.slf4j.Slf4j;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;import java.util.concurrent.*;@Slf4j
@Configuration
public class CommonConfig {Thread.UncaughtExceptionHandler exceptionHandler = (Thread t, Throwable e) -> {log.info("current thread occurs error！", e);};@Beanpublic ThreadPoolExecutor executor() {ThreadFactory threadFactory = new ThreadFactoryBuilder().setUncaughtExceptionHandler(exceptionHandler).setNameFormat("mouse-worker-%d").build();int processors = Runtime.getRuntime().availableProcessors();log.info("processors:{}", processors);ThreadPoolExecutor executor = new ThreadPoolExecutor(1,processors * 2,0L,TimeUnit.MILLISECONDS,new LinkedBlockingDeque<>(1000),threadFactory,new ThreadPoolExecutor.AbortPolicy());return executor;}/*** 使用阿里的 TransmittableThreadLocal 装饰线程池* @return*/@Beanpublic Executor ttlExecutor() {ThreadFactory threadFactory = new ThreadFactoryBuilder().setUncaughtExceptionHandler(exceptionHandler).setNameFormat("mouse-worker-ttl-%d").build();int processors = Runtime.getRuntime().availableProcessors();log.info("processors:{}", processors);ThreadPoolExecutor executor = new ThreadPoolExecutor(1,processors * 2,0L,TimeUnit.MILLISECONDS,new LinkedBlockingDeque<>(1000),threadFactory,new ThreadPoolExecutor.AbortPolicy());Executor ttlExecutor = TtlExecutors.getTtlExecutor(executor);return ttlExecutor;}}

这里线程池的核心线程数设置为1，是为了方便测试，和这篇文章的思路一致web项目国际化指南

 

测试代码

package com.tml.mouseDemo.controller;import com.tml.mouseDemo.constants.CommonResponse;
import com.tml.mouseDemo.service.TraceService;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RestController;import java.util.concurrent.Executor;
import java.util.concurrent.ThreadPoolExecutor;@RestController
@Slf4j
public class TraceController {@Autowiredprivate ThreadPoolExecutor executor;@Autowiredprivate Executor ttlExecutor;@Autowiredprivate TraceService traceService;@PostMapping("/traceWithThreadPool")public CommonResponse<String> traceWithThreadPool(String type) throws InterruptedException {log.info("traceWithThreadPool type:{}", type);traceService.trace(type);//模拟异步发短信executor.execute(() -> {try {Thread.sleep(2000);String sendMsg = "hello world";log.info("sendMsg:{}", sendMsg);} catch (Exception e) {log.error("traceWithThreadPool occur error", e);}});//模拟异步发短信ttlExecutor.execute(() -> {try {Thread.sleep(2000);String sendMsg = "hello world";log.info("sendMsg:{}", sendMsg);} catch (Exception e) {log.error("traceWithThreadPool occur error", e);}});return CommonResponse.success("success");}
}

运行两次，看下效果

 

 可以看到，使用ttl装饰的线程池的日志是正常的，使用普通的线程池的日志的traceId错乱了，这个也是尤其需要注意的点。

总结

在logback中，可以使用多种方式来自定义占位符，通常一般的做法主要是上面两种。使用MDC的方式就是简单，不过他的缺陷也是显而易见的，就是他不支持多线程的数据传递。

所以，如果你的项目中想要自定义占位符，强烈建议使用自定义Convertor的方式。详细的代码已上传至github，欢迎前来围观我的github

常见的日志占位符总结

这里总结下logback中常见的占位符，欢迎补充

占位符名称	占位符含义	备注
%d	日期和时间	%d{HH:mm:ss.SSS} %d{yyyy-MM-dd HH:mm:ss} 可以自定义时间的格式
%t	线程名称
%p	日志的优先级
%c	日志记录器名称	一般表示类名，可以%c{20}，可以通过 这样来设置类名的最大长度
%m	日志消息
%n	换行符
%L	日志行号
%X{key}	代表 MDC中存储的 key 对应的信息	不建议使用，不支持多线程