spring-cloud-sleuth+zipkin源码探究

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());
	}

2. 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));
	}
}

2. 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