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