spring-cloud Sleuth的使用方法

 public static Filter create(HttpTracing httpTracing) {  return new TracingFilter(httpTracing); } //Servlet运行时类 final ServletRuntime servlet = ServletRuntime.get(); //Slf4jCurrentTraceContext final CurrentTraceContext currentTraceContext; final Tracer tracer; final HttpServerHandler<HttpServletRequest, HttpServletResponse> handler; //TraceContext的数据提取器 final TraceContext.Extractor<HttpServletRequest> extractor; TracingFilter(HttpTracing httpTracing) {  tracer = httpTracing.tracing().tracer();  currentTraceContext = httpTracing.tracing().currentTraceContext();  handler = HttpServerHandler.create(httpTracing, ADAPTER);  extractor = httpTracing.tracing().propagation().extractor(GETTER); }

  Tracing tracing;  //客户端span解析器  HttpClientParser clientParser;  String serverName;  //服务端span解析器  HttpServerParser serverParser;  HttpSampler clientSampler, serverSampler;  Builder(Tracing tracing) {   if (tracing == null) throw new NullPointerException("tracing == null");   final ErrorParser errorParser = tracing.errorParser();   this.tracing = tracing;   this.serverName = "";   // override to re-use any custom error parser from the tracing component   this.clientParser = new HttpClientParser() {    @Override protected ErrorParser errorParser() {     return errorParser;    }   };   this.serverParser = new HttpServerParser() {    @Override protected ErrorParser errorParser() {     return errorParser;    }   };   this.clientSampler = HttpSampler.TRACE_ID;   this.serverSampler(HttpSampler.TRACE_ID);  }

  @Bean  @ConditionalOnMissingBean  // NOTE: stable bean name as might be used outside sleuth  Tracing tracing(@Value("${spring.zipkin.service.name:${spring.application.name:default}}") String serviceName,      Propagation.Factory factory,      CurrentTraceContext currentTraceContext,      Reporter<zipkin2.Span> reporter,      Sampler sampler,      ErrorParser errorParser,      SleuthProperties sleuthProperties  ) {    return Tracing.newBuilder()        .sampler(sampler)        .errorParser(errorParser)        .localServiceName(serviceName)        //ExtraFieldPropagation.Factory        .propagationFactory(factory)        .currentTraceContext(currentTraceContext)        .spanReporter(adjustedReporter(reporter))        .traceId128Bit(sleuthProperties.isTraceId128())        .supportsJoin(sleuthProperties.isSupportsJoin())        .build();  }

  Span span = handler.handleReceive(extractor, httpRequest);  // Add attributes for explicit access to customization or span context  request.setAttribute(SpanCustomizer.class.getName(), span.customizer());  request.setAttribute(TraceContext.class.getName(), span.context());  Throwable error = null;  Scope scope = currentTraceContext.newScope(span.context());  try {   // any downstream code can see Tracer.currentSpan() or use Tracer.currentSpanCustomizer()   chain.doFilter(httpRequest, httpResponse);  } catch (IOException | ServletException | RuntimeException | Error e) {   error = e;   throw e;  } finally {   scope.close();   if (servlet.isAsync(httpRequest)) { // we don't have the actual response, handle later    servlet.handleAsync(handler, httpRequest, httpResponse, span);   } else { // we have a synchronous response, so we can finish the span    handler.handleSend(ADAPTER.adaptResponse(httpRequest, httpResponse), error, span);   }  } }

 @Configuration  @ConditionalOnClass(MDC.class)  @EnableConfigurationProperties(SleuthSlf4jProperties.class)  protected static class Slf4jConfiguration {    @Bean    @ConditionalOnProperty(value = "spring.sleuth.log.slf4j.enabled", matchIfMissing = true)    @ConditionalOnMissingBean    public CurrentTraceContext slf4jSpanLogger() {      return Slf4jCurrentTraceContext.create();    }        ...   }

 public static final class Default extends CurrentTraceContext {  static final ThreadLocal<TraceContext> DEFAULT = new ThreadLocal<>();  // Inheritable as Brave 3's ThreadLocalServerClientAndLocalSpanState was inheritable  static final InheritableThreadLocal<TraceContext> INHERITABLE = new InheritableThreadLocal<>();  final ThreadLocal<TraceContext> local;  //静态方法create，local对象为ThreadLocal类型   /** Uses a non-inheritable static thread local */  public static CurrentTraceContext create() {   return new Default(DEFAULT);  }  //local对象为InheritableThreadLocal类型  //官方文档指出，inheritable方法在线程池的环境中需谨慎使用，可能会取出错误的TraceContext，这样会导致Span等信息会记录并关联到错误的traceId上  /**   * Uses an inheritable static thread local which allows arbitrary calls to {@link   * Thread#start()} to automatically inherit this context. This feature is available as it is was   * the default in Brave 3, because some users couldn't control threads in their applications.   *   * <p>This can be a problem in scenarios such as thread pool expansion, leading to data being   * recorded in the wrong span, or spans with the wrong parent. If you are impacted by this,   * switch to {@link #create()}.   */  public static CurrentTraceContext inheritable() {   return new Default(INHERITABLE);  }  Default(ThreadLocal<TraceContext> local) {   if (local == null) throw new NullPointerException("local == null");   this.local = local;  }  @Override public TraceContext get() {   return local.get();  }  //替换当前TraceContext，close方法将之前的TraceContext设置回去  //Scope接口继承了Closeable接口，在try中使用会自动调用close方法，为了避免用户忘记close方法，还提供了Runnable，Callable，Executor，ExecutorService包装方法  @Override public Scope newScope(@Nullable TraceContext currentSpan) {   final TraceContext previous = local.get();   local.set(currentSpan);   class DefaultCurrentTraceContextScope implements Scope {    @Override public void close() {     local.set(previous);    }   }   return new DefaultCurrentTraceContextScope();  } }

 //返回一个新的scope，如果当前scope就是传入的scope，返回一个空scope public Scope maybeScope(@Nullable TraceContext currentSpan) {  //获取当前TraceContext  TraceContext currentScope = get();  //如果传入的TraceContext为空，且当前TraceContext为空返回空scope  if (currentSpan == null) {   if (currentScope == null) return Scope.NOOP;   return newScope(null);  }  return currentSpan.equals(currentScope) ? Scope.NOOP : newScope(currentSpan); }