分布式跟踪系统Zipkin详解(5)

创建一个Brave

private Brave(Builder builder) { serverTracer = ServerTracer.builder() .randomGenerator(builder.random) .spanCollector(builder.spanCollector) .state(builder.state) .traceSampler(builder.sampler).build(); clientTracer = ClientTracer.builder() .randomGenerator(builder.random) .spanCollector(builder.spanCollector) .state(builder.state) .traceSampler(builder.sampler).build(); localTracer = LocalTracer.builder() .randomGenerator(builder.random) .spanCollector(builder.spanCollector) .spanAndEndpoint(SpanAndEndpoint.LocalSpanAndEndpoint.create(builder.state)) .traceSampler(builder.sampler).build(); serverRequestInterceptor = new ServerRequestInterceptor(serverTracer); serverResponseInterceptor = new ServerResponseInterceptor(serverTracer); clientRequestInterceptor = new ClientRequestInterceptor(clientTracer); clientResponseInterceptor = new ClientResponseInterceptor(clientTracer); serverSpanAnnotationSubmitter = AnnotationSubmitter.create(SpanAndEndpoint.ServerSpanAndEndpoint.create(builder.state)); serverSpanThreadBinder = new ServerSpanThreadBinder(builder.state); clientSpanThreadBinder = new ClientSpanThreadBinder(builder.state); }

封装了*Tracer,*Interceptor,*Binder等

其中 serverTracer当服务作为服务端时处理span信息，clientTracer当服务作为客户端时处理span信息

Filter

BraveServletFilter是http模块提供的拦截器功能，传递serverRequestInterceptor,serverResponseInterceptor,spanNameProvider等参数
其中spanNameProvider表示如何处理span的名称，默认使用method名称,spring boot中申明的filter bean 默认拦截所有请求

@Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException { String alreadyFilteredAttributeName = getAlreadyFilteredAttributeName(); boolean hasAlreadyFilteredAttribute = request.getAttribute(alreadyFilteredAttributeName) != null; if (hasAlreadyFilteredAttribute) { // Proceed without invoking this filter... filterChain.doFilter(request, response); } else { final StatusExposingServletResponse statusExposingServletResponse = new StatusExposingServletResponse((HttpServletResponse) response); requestInterceptor.handle(new HttpServerRequestAdapter(new ServletHttpServerRequest((HttpServletRequest) request), spanNameProvider)); try { filterChain.doFilter(request, statusExposingServletResponse); } finally { responseInterceptor.handle(new HttpServerResponseAdapter(new HttpResponse() { @Override public int getHttpStatusCode() { return statusExposingServletResponse.getStatus(); } })); } } }

首先来看requestInterceptor.handle方法，

public void handle(ServerRequestAdapter adapter) { serverTracer.clearCurrentSpan(); final TraceData traceData = adapter.getTraceData(); Boolean sample = traceData.getSample(); if (sample != null && Boolean.FALSE.equals(sample)) { serverTracer.setStateNoTracing(); LOGGER.fine("Received indication that we should NOT trace."); } else { if (traceData.getSpanId() != null) { LOGGER.fine("Received span information as part of request."); SpanId spanId = traceData.getSpanId(); serverTracer.setStateCurrentTrace(spanId.traceId, spanId.spanId, spanId.nullableParentId(), adapter.getSpanName()); } else { LOGGER.fine("Received no span state."); serverTracer.setStateUnknown(adapter.getSpanName()); } serverTracer.setServerReceived(); for(KeyValueAnnotation annotation : adapter.requestAnnotations()) { serverTracer.submitBinaryAnnotation(annotation.getKey(), annotation.getValue()); } } }

其中serverTracer.clearCurrentSpan()清除当前线程上的span信息，调用ThreadLocalServerClientAndLocalSpanState中的

@Override public void setCurrentServerSpan(final ServerSpan span) { if (span == null) { currentServerSpan.remove(); } else { currentServerSpan.set(span); } }

currentServerSpan为ThreadLocal对象

private final static ThreadLocal<ServerSpan> currentServerSpan = new ThreadLocal<ServerSpan>() {