spring-cloud-sleuth+zipkin源码探究

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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

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
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

当启动初始化程序时，跟踪代码如下

    @Beanpublic FilterRegistrationBean traceWebFilter(TraceFilter traceFilter) {FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(traceFilter);filterRegistrationBean.setDispatcherTypes(ASYNC, ERROR, FORWARD, INCLUDE,REQUEST);filterRegistrationBean.setOrder(TraceFilter.ORDER);return filterRegistrationBean;}@Bean@ConditionalOnMissingBeanpublic TraceFilter traceFilter(BeanFactory beanFactory,SkipPatternProvider skipPatternProvider) {return new TraceFilter(beanFactory, skipPatternProvider.skipPattern());}

初始化traceFilter，进行过滤器注册

1.2.3. 拦截器注册

然后看TraceWebMvcConfigurer类，它会进行拦截器的注册

@Configuration
class TraceWebMvcConfigurer extends WebMvcConfigurerAdapter {@Autowired BeanFactory beanFactory;@Beanpublic TraceHandlerInterceptor traceHandlerInterceptor(BeanFactory beanFactory) {return new TraceHandlerInterceptor(beanFactory);}@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(this.beanFactory.getBean(TraceHandlerInterceptor.class));}
}

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

    @Overridepublic 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;}

    @Overridepublic 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

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

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;}