利用Spring

利⽤Spring boot+LogBack+MDC实现链路追踪
⽬录
MDC介绍
API说明
MDC使⽤
1.拦截器
2.⼯具类
MDC 存在的问题
⼦线程⽇志打印丢失traceId
HTTP调⽤丢失traceId
1.接⼝调⽤⽅
2.第三⽅服务需要添加拦截器
MDC介绍
MDC(Mapped Diagnostic Context，映射调试上下⽂)是 log4j 、logback及log4j2 提供的⼀种⽅便在多线程条件下记录⽇志的功能。

MDC 可以看成是⼀个与当前线程绑定的哈希表，可以往其中添加键值对。

MDC 中包含的内容可以被同⼀线程中执⾏的代码所访问。

当前线程的⼦线程会继承其⽗线程中的 MDC 的内容。

当需要记录⽇志时，只需要从 MDC 中获取所需的信息即可。

API说明
clear() => 移除所有MDC
get (String key) => 获取当前线程MDC中指定key的值
getContext() => 获取当前线程MDC的MDC
put(String key, Object o) => 往当前线程的MDC中存⼊指定的键值对
remove(String key) => 删除当前线程MDC中指定的键值对。

MDC使⽤
1.拦截器
@Component
public class LogInterceptor implements HandlerInterceptor
{
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
//如果有上层调⽤就⽤上层的ID
String traceId = request.getHeader(TraceIdUtil.TRACE_ID);
if (StringUtil.isEmpty(traceId))
{
TraceIdUtil.setTraceId(TraceIdUtil.generateTraceId());
}
else
{
TraceIdUtil.setTraceId(traceId);
}
return true;
}
@Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
throws Exception
{
}
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
throws Exception {
//调⽤结束后删除
TraceIdUtil.remove();
}
}
2.⼯具类
public class TraceIdUtil
{
public static final String TRACE_ID = "requestId";
public static String getTraceId()
{
String traceId =(String) MDC.get(TRACE_ID);
return traceId == null ? "" : traceId;
}
public static void setTraceId(String traceId)
{
MDC.put(TRACE_ID,traceId);
}
public static void remove()
{
MDC.remove(TRACE_ID);
}
public static void clear()
{
MDC.clear();
}
public static String generateTraceId() {
return UUID.randomUUID().toString().replace("-", "");
}
⽇志⽂件配置
<property name="LOG_PATTERN" value="%date{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level [%X{requestId}] %logger{36} - %msg%n" />
重点是%X{requestId},requestId和MDC中的键名称保持⼀致。

MDC 存在的问题
⾄此基本的功能已经实现，但是存在⼀下⼏个问题
多线程情况下，⼦线程中打印⽇志会丢失traceId.
HTTP跨服务之间的调⽤丢失traceId.
⼦线程⽇志打印丢失traceId
问题重现：
@LogAnnotation(model="⽤户管理",func="查询⽤户信息",desc="根据⽤户名称")
@GetMapping("getUserByName")
public Result getUserByName(@RequestParam String name)
{
//主线程⽇志
("getUserByName paramter name:"+name);
for(int i=0;i<5;i++)
{
//⼦线程⽇志
threadPoolTaskExecutor.execute(()->{
("child thread:{}",name);
userService.getUserByName(name);
});
}
return Result.success();
}
运⾏结果：
2022-03-13 12:45:44.156 [http-nio-8089-exec-1] INFO [ec05a600ed1a4556934a3afa4883766a]
erController - getUserByName paramter name:1
2022-03-13 12:45:44.173 [Pool-A1] INFO [] erController - child thread:1
从运⾏的结果来看，⼦线程打印⽇志，⽇志中的traceId信息已经丢失。

解决⽅案：
⼦线程在打印⽇志的过程中traceId将丢失，解决⽅案为重写线程池(对于直接new Thread 创建线程的情况不考略),实际开发中也需要禁⽌这种情况。

public class ThreadPoolExecutorMdcWrapper extends ThreadPoolTaskExecutor
private static final long serialVersionUID = 3940722618853093830L;
@Override
public void execute(Runnable task)
{
super.execute(ThreadMdcUtil.wrap(task, MDC.getCopyOfContextMap()));
}
@Override
public <T> Future<T> submit(Callable<T> task)
{
return super
.submit(ThreadMdcUtil.wrap(task, MDC.getCopyOfContextMap()));
}
@Override
public Future<?> submit(Runnable task)
{
return super
.submit(ThreadMdcUtil.wrap(task, MDC.getCopyOfContextMap()));
}
}
因为Spring Boot ThreadPoolTaskExecutor 已经对ThreadPoolExecutor进⾏封装，只需要继承ThreadPoolTaskExecutor重写相关的执⾏⽅法即可。

public class ThreadMdcUtil
{
public static void setTraceIdIfAbsent() {
if (MDC.get(TraceIdUtil.TRACE_ID) == null)
{
MDC.put(TraceIdUtil.TRACE_ID, TraceIdUtil.generateTraceId());
}
}
public static <T> Callable<T> wrap(final Callable<T> callable, final Map<String, String> context) {
return () -> {
if (context == null) {
MDC.clear();
} else {
MDC.setContextMap(context);
}
setTraceIdIfAbsent();
try {
return callable.call();
} finally {
MDC.clear();
}
};
}
public static Runnable wrap(final Runnable runnable, final Map<String, String> context) {
return () -> {
if (context == null) {
MDC.clear();
} else {
MDC.setContextMap(context);
}
//设置traceId
setTraceIdIfAbsent();
try {
runnable.run();
} finally {
MDC.clear();
}
};
}
}
代码说明：
判断当前线程对应MDC的Map是否存在，如果存在则设置
设置MDC中的traceId值，不存在则新⽣成，如果是⼦线程，MDC中traceId不为null
执⾏run⽅法
线程池配置
@Configuration
public class ThreadPoolTaskExecutorConfig
//最⼤可⽤的CPU核数
public static final int PROCESSORS = Runtime.getRuntime().availableProcessors();
@Bean
public ThreadPoolExecutorMdcWrapper getExecutor()
{
ThreadPoolExecutorMdcWrapper executor =new ThreadPoolExecutorMdcWrapper();
executor.setCorePoolSize(PROCESSORS *2);
executor.setMaxPoolSize(PROCESSORS * 4);
executor.setQueueCapacity(50);
executor.setKeepAliveSeconds(60);
executor.setThreadNamePrefix("Task-A");
executor.setRejectedExecutionHandler(new ThreadPoolExecutor.AbortPolicy());
executor.initialize();
return executor;
}
}
重新运⾏结果发现⼦线程能够正常获取traceid信息进⾏跟踪。

2022-03-13 13:19:30.688 [Task-A1] INFO [482929425cbc4476a4e7168615af7890]
erController - child thread:1
2022-03-13 13:19:31.003 [Task-A1] INFO [482929425cbc4476a4e7168615af7890]
erServiceImpl - name:1
HTTP调⽤丢失traceId
HTTP调⽤第三⽅服务接⼝时traceId丢失，需要在发送请求时在Request Header中添加traceId，在被调⽤⽅添加拦截器获取header中的traceId添加到MDC中。

HTTP调⽤有多种⽅式，⽐较常见的有HttpClient、OKHttp、RestTemplate，以RestTemplate调⽤为例。

1.接⼝调⽤⽅
public class RestTemplateTraceIdInterceptor implements
ClientHttpRequestInterceptor
{
@Override
public ClientHttpResponse intercept(HttpRequest request, byte[] body,
ClientHttpRequestExecution clientHttpRequestExecution) throws IOException
{
String traceId=MDC.get("requestId");
if(traceId!=null)
{
request.getHeaders().set("requestId", traceId);
}
else
{
request.getHeaders().set("requestId", UUID.randomUUID().toString().replace("-", ""));
}
return clientHttpRequestExecution.execute(request, body);
}
}
RestTemplate添加拦截器即可。

restTemplate.setInterceptors(Arrays.asList(new RestTemplateTraceIdInterceptor()));
复制代码
2.第三⽅服务需要添加拦截器
@Component
public class LogInterceptor implements HandlerInterceptor
{
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
//如果有上层调⽤就⽤上层的ID
String traceId = request.getHeader(TraceIdUtil.TRACE_ID);
if (StringUtil.isEmpty(traceId))
{
TraceIdUtil.setTraceId(TraceIdUtil.generateTraceId());
}
else
{
TraceIdUtil.setTraceId(traceId);
}
return true;
}
@Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
throws Exception
{
}
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
throws Exception {
//调⽤结束后删除
TraceIdUtil.remove();
}
}
其他HttpClient、OKHttp的实现⽅式与RestTemplate基本相同，这⾥就不⼀⼀列举。

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