1. spring-cloud-sleuth+zipkin源码探究

1.1. 前言

  粗略看了下spring cloud sleuth core源码，发现内容真的有点多，它支持了很多类型的链路追踪，我就找其中一个比较有代表性的深入剖析下源码结构和内容

1.2. spring-cloud-sleuth-core源码解析

1.2.1. 结构

1. 可以看到源码中支持的追踪类型有很多，支持async，hystrix，websocket，rxjava，Spring mvc，servlet，spring restTemplate，feign，zuul等等，这里我着重探讨spring web mvc的链路追踪
2. 打开web包，找到TraceWebAutoConfiguration，这里配置了主要的初始化类
   
   

1.2.2. 过滤器注册

1. 当启动初始化程序时，跟踪代码如下

	@Bean

	public FilterRegistrationBean traceWebFilter(TraceFilter traceFilter) {

		FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(

				traceFilter);

		filterRegistrationBean.setDispatcherTypes(ASYNC, ERROR, FORWARD, INCLUDE,

				REQUEST);

		filterRegistrationBean.setOrder(TraceFilter.ORDER);

		return filterRegistrationBean;

	}

	@Bean

	@ConditionalOnMissingBean

	public TraceFilter traceFilter(BeanFactory beanFactory,

			SkipPatternProvider skipPatternProvider) {

		return new TraceFilter(beanFactory, skipPatternProvider.skipPattern());

	}

1. 初始化traceFilter，进行过滤器注册

1.2.3. 拦截器注册

1. 然后看TraceWebMvcConfigurer类，它会进行拦截器的注册

@Configuration

class TraceWebMvcConfigurer extends WebMvcConfigurerAdapter {

	@Autowired BeanFactory beanFactory;

	@Bean

	public TraceHandlerInterceptor traceHandlerInterceptor(BeanFactory beanFactory) {

		return new TraceHandlerInterceptor(beanFactory);

	}

	@Override

	public void addInterceptors(InterceptorRegistry registry) {

		registry.addInterceptor(this.beanFactory.getBean(TraceHandlerInterceptor.class));

	}

}

1. 在TraceHandlerInterceptor类中，preHandle,afterCompletion方法可以看出，这是对请求进行拦截进行span的包装

	@Override

	public boolean preHandle(HttpServletRequest request, HttpServletResponse response,

			Object handler) throws Exception {

		String spanName = spanName(handler);

		boolean continueSpan = getRootSpanFromAttribute(request) != null;

		Span span = continueSpan ? getRootSpanFromAttribute(request) : getTracer().createSpan(spanName);

		if (log.isDebugEnabled()) {

			log.debug("Handling span " + span);

		}

		addClassMethodTag(handler, span);

		addClassNameTag(handler, span);

		setSpanInAttribute(request, span);

		if (!continueSpan) {

			setNewSpanCreatedAttribute(request, span);

		}

		return true;

	}

	@Override

	public void afterCompletion(HttpServletRequest request, HttpServletResponse response,

			Object handler, Exception ex) throws Exception {

		if (isErrorControllerRelated(request)) {

			if (log.isDebugEnabled()) {

				log.debug("Skipping closing of a span for error controller processing");

			}

			return;

		}

		Span span = getRootSpanFromAttribute(request);

		if (ex != null) {

			getErrorParser().parseErrorTags(span, ex);

		}

		if (getNewSpanFromAttribute(request) != null) {

			if (log.isDebugEnabled()) {

				log.debug("Closing span " + span);

			}

			Span newSpan = getNewSpanFromAttribute(request);

			getTracer().continueSpan(newSpan);

			getTracer().close(newSpan);

			clearNewSpanCreatedAttribute(request);

		}

	}

1.2.4. zipkin端点提交

1. 这里首先会初始化HttpZipkinSpanReporter类，，用来进行span端点提交，然后初始化ZipkinSpanListenerspan的监听器，用来监听并调用端点提交，以上配置再下图位置
   
   

1.2.5. 调用http接口时，进入过滤器

1. 首先进入TraceFilter中的过滤方法doFilter，这里会做span的创建

private Span createSpan(HttpServletRequest request,

			boolean skip, Span spanFromRequest, String name) {

		if (spanFromRequest != null) {

			if (log.isDebugEnabled()) {

				log.debug("Span has already been created - continuing with the previous one");

			}

			return spanFromRequest;

		}

		//加入调用链路ZipkinHttpSpanExtractor，此链路在TraceHttpAutoConfiguration中配置实例化，调用链还没有时，返回为空，作为头节点

		Span parent = spanExtractor().joinTrace(new HttpServletRequestTextMap(request));

		if (parent != null) {

			if (log.isDebugEnabled()) {

				log.debug("Found a parent span " + parent + " in the request");

			}

			addRequestTagsForParentSpan(request, parent);

			spanFromRequest = parent;

			tracer().continueSpan(spanFromRequest);

			if (parent.isRemote()) {

				parent.logEvent(Span.SERVER_RECV);

			}

			request.setAttribute(TRACE_REQUEST_ATTR, spanFromRequest);

			if (log.isDebugEnabled()) {

				log.debug("Parent span is " + parent + "");

			}

		} else {

			if (skip) {

				spanFromRequest = tracer().createSpan(name, NeverSampler.INSTANCE);

			}

			else {

				String header = request.getHeader(Span.SPAN_FLAGS);

				if (Span.SPAN_SAMPLED.equals(header)) {

					spanFromRequest = tracer().createSpan(name, new AlwaysSampler());

				} else {

				//创建span节点

					spanFromRequest = tracer().createSpan(name);

				}

			}

			spanFromRequest.logEvent(Span.SERVER_RECV);

			request.setAttribute(TRACE_REQUEST_ATTR, spanFromRequest);

			if (log.isDebugEnabled()) {

				log.debug("No parent span present - creating a new span");

			}

		}

		return spanFromRequest;

	}

1.2.6. 进入拦截器

1. 在preHandle方法中，对span进行包装，然后把span放入请求头header中
2. 最后再DefaultTracer中进行span的关闭和spanReporter的提交

参考：https://blog.csdn.net/zhllansezhilian/article/details/83001870