本系列代码地址： https://github.com/JoJoTec/spring-cloud-parent
我们在这一节我们将继续讲解避免链路信息丢失做的设计，主要针对获取到现有 Span 之后，如何保证每个 GlobalFilter 都能保持链路信息。首先，我们自定义 Reactor 的核心 Publisher 即 Mono 和 Flux 的工厂，将链路信息封装进去，保证由这个工厂生成的 Mono 和 Flux，都是只要是这个工厂生成的 Mono 和 Flux 之间无论怎么拼接都会保持链路信息的：
自定义 Mono 和 Flux 的工厂
公共 Subscriber 封装，将 reactor Subscriber 的所有关键接口，都检查当前上下文是否有链路信息，即 Span，如果没有就包裹上，如果有则直接执行即可。
public class TracedCoreSubscriber<T> implements Subscriber<T>{ private final Subscriber<T> delegate; private final Tracer tracer; private final CurrentTraceContext currentTraceContext; private final Span span; TracedCoreSubscriber(Subscriber<T> delegate, Tracer tracer, CurrentTraceContext currentTraceContext, Span span) { this.delegate = delegate; this.tracer = tracer; this.currentTraceContext = currentTraceContext; this.span = span; } @Override public void onSubscribe(Subscription s) { executeWithinScope(() -> { delegate.onSubscribe(s); }); } @Override public void onError(Throwable t) { executeWithinScope(() -> { delegate.onError(t); }); } @Override public void onComplete() { executeWithinScope(() -> { delegate.onComplete(); }); } @Override public void onNext(T o) { executeWithinScope(() -> { delegate.onNext(o); }); } private void executeWithinScope(Runnable runnable) { //如果当前没有链路信息，强制包裹 if (tracer.currentSpan() == null) { try (CurrentTraceContext.Scope scope = this.currentTraceContext.maybeScope(this.span.context())) { runnable.run(); } } else { //如果当前已有链路信息，则直接执行 runnable.run(); } } }
之后分别定义所有 Flux 的代理 TracedFlux，和所有 Mono 的代理 TracedMono，其实就是在 subscribe 的时候，用 TracedCoreSubscriber 包装传入的 CoreSubscriber：
public class TracedFlux<T> extends Flux<T> { private final Flux<T> delegate; private final Tracer tracer; private final CurrentTraceContext currentTraceContext; private final Span span; TracedFlux(Flux<T> delegate, Tracer tracer, CurrentTraceContext currentTraceContext, Span span) { this.delegate = delegate; this.tracer = tracer; this.currentTraceContext = currentTraceContext; this.span = span; } @Override public void subscribe(CoreSubscriber<? super T> actual) { delegate.subscribe(new TracedCoreSubscriber(actual, tracer, currentTraceContext, span)); } } public class TracedMono<T> extends Mono<T> { private final Mono<T> delegate; private final Tracer tracer; private final CurrentTraceContext currentTraceContext; private final Span span; TracedMono(Mono<T> delegate, Tracer tracer, CurrentTraceContext currentTraceContext, Span span) { this.delegate = delegate; this.tracer = tracer; this.currentTraceContext = currentTraceContext; this.span = span; } @Override public void subscribe(CoreSubscriber<? super T> actual) { delegate.subscribe(new TracedCoreSubscriber(actual, tracer, currentTraceContext, span)); } }
定义工厂类，使用请求 ServerWebExchange 和原始 Flux 创建 TracedFlux，以及使用请求 ServerWebExchange 和原始 Mono 创建 TracedMono，并且 Span 是通过 Attributes 获取的，根据前文的源码分析我们知道，这个 Attribute 是通过 TraceWebFilter 放入 Attributes 的。由于我们只在 GatewayFilter 中使用，一定在 TraceWebFilter 之后 所以这个 Attribute 一定存在。
@Component public class TracedPublisherFactory { protected static final String TRACE_REQUEST_ATTR = Span.class.getName(); @Autowired private Tracer tracer; @Autowired private CurrentTraceContext currentTraceContext; public <T> Flux<T> getTracedFlux(Flux<T> publisher, ServerWebExchange exchange) { return new TracedFlux<>(publisher, tracer, currentTraceContext, (Span) exchange.getAttributes().get(TRACE_REQUEST_ATTR)); } public <T> Mono<T> getTracedMono(Mono<T> publisher, ServerWebExchange exchange) { return new TracedMono<>(publisher, tracer, currentTraceContext, (Span) exchange.getAttributes().get(TRACE_REQUEST_ATTR)); } }
公共抽象 GlobalFilter - CommonTraceFilter
我们编写所有我们后面要实现的 GlobalFilter 的抽象类，这个抽象类的主要功能是：
- 保证继承这个抽象类的 GlobalFilter 本身以及拼接的链路中，是有链路信息的，其实就是保证它 filter 返回的 Mono<Void> 是由我们上面实现的 Factory 生成的即可。
- 不同 GlobalFilter 之间需要排序，有顺序的执行，这个通过实现 Ordered 接口即可
package com.github.jojotech.spring.cloud.apigateway.filter; import com.github.jojotech.spring.cloud.apigateway.common.TraceWebFilterUtil; import com.github.jojotech.spring.cloud.apigateway.common.TracedPublisherFactory; import reactor.core.publisher.Mono; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.cloud.gateway.filter.GatewayFilterChain; import org.springframework.cloud.gateway.filter.GlobalFilter; import org.springframework.cloud.sleuth.CurrentTraceContext; import org.springframework.cloud.sleuth.Span; import org.springframework.cloud.sleuth.Tracer; import org.springframework.core.Ordered; import org.springframework.web.server.ServerWebExchange; /** * 所有 filter 的子类 * 主要保证 span 的完整性，在某些情况下，span 会半途停止，导致日志中没有 traceId 和 spanId * 参考：https://github.com/spring-cloud/spring-cloud-sleuth/issues/2004 */ public abstract class AbstractTracedFilter implements GlobalFilter, Ordered { @Autowired protected Tracer tracer; @Autowired protected TracedPublisherFactory tracedPublisherFactory; @Autowired protected CurrentTraceContext currentTraceContext; @Override public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) { Mono<Void> traced; if (tracer.currentSpan() == null) { try (CurrentTraceContext.Scope scope = this.currentTraceContext .maybeScope(((Span) exchange.getAttributes().get(TraceWebFilterUtil.TRACE_REQUEST_ATTR)) .context())) { traced = traced(exchange, chain); } } else { //如果当前已有链路信息，则直接执行 traced = traced(exchange, chain); } return tracedPublisherFactory.getTracedMono(traced, exchange); } protected abstract Mono<Void> traced(ServerWebExchange exchange, GatewayFilterChain chain); }
这样，我们就可以基于这个抽象类去实现需要定制的 GlobalFilter 了
