Gateway源码分析：路由Route、断言Predicate、Filter

源码总流程图

在线总流程图

说明

Gateway的版本使用的是4.0.0

Gateway的实现是基于WebFlux 、Reactor 、Netty

Gateway微服务的yml配置如下

• Gateway的访问端口为8888
• id为order_route的路由 uri为lb://mall-order
• 为mall-order这个微服务定义了一个path路径的predicate断言；定义了三个filter

server:port: 8888
spring:application:name: mall-gateway#配置nacos注册中心地址cloud:nacos:discovery:server-addr: nacos.mall.com:8848username: nacospassword: nacosgateway:#设置路由：路由id、路由到微服务的uri、断言routes:- id: user_route   #路由ID，全局唯一uri: lb://mall-user  #lb 整合负载均衡器ribbon,loadbalancerpredicates:- Path=/user/**   # 断言，路径相匹配的进行路由- id: order_route  #路由ID，全局唯一# 测试 http://localhost:8888/order/findOrderByUserId/1uri: lb://mall-order  #lb 整合负载均衡器loadbalancerpredicates:- Path=/order/**   # 断言，路径相匹配的进行路由#配置过滤器工厂filters:- AddRequestHeader=X-Request-color, red  #添加请求头- AddRequestParameter=color, blue  # 添加请求参数- CheckAuth=hushang,男  #自定义过滤器工厂

Gateway的工作原理就是下面这一张图

在开始看Gateway的源码之前，我们回忆一下SpringMVC的实现原理：

1. DispatchServlet#doDispatch作为Springmvc的入口
2. HandlerMapper 路由匹配 —> 找到Handler
3. 通过handler 找的适配的 HandlerAdapter
4. HandlerAdapter#handle方法执行

而在Gateway的源码中：

• DispatcherHandler#handle作为入口
• HandlerMapping 路由匹配 --> 断言predicate匹配 RoutePredicateHandlerMapping#getHandlerInternal，找到路由Route对象
• 返回FilteringWebHandler
• HandlerAdapter 适配器 SimpleHandlerAdapter#handle 处理WebHandler
• 进入到org.springframework.cloud.gateway.handler.FilteringWebHandler#handle —> filterChain处理

Flux和Mono的概念

Reactor学习文档

Flux：

Mono：

GateWayAutoConfiguration

在GatewayAutoConfiguration自动配置类中，它配置了很多bean对象，常见的就比如：

// 保存我们配置文件中关于网关路由相关的所有配置
// GatewayProperties保存了List<RouteDefinition>
// 而RouteDefinition就是每一个路由对象，保存了id、uri、断言集合List<PredicateDefinition>、Filter集合List<FilterDefinition>
@Bean
public GatewayProperties gatewayProperties() {return new GatewayProperties();
}// Path路径匹配的断言工厂，断言相关的bean都是以RoutePredicateFactory结尾
@Bean
@ConditionalOnEnabledPredicate
public PathRoutePredicateFactory pathRoutePredicateFactory() {return new PathRoutePredicateFactory();
}// 添加请求头的Filter，一般都是以GatewayFilterFactory
@Bean
@ConditionalOnEnabledFilter
public AddRequestHeaderGatewayFilterFactory addRequestHeaderGatewayFilterFactory() {return new AddRequestHeaderGatewayFilterFactory();
}// 全局过滤器，把我们访问网关的url转换为路由中配置的uri
// http://localhost:8888/order/findOrderByUserId/1  --->  lb://mall-order/order/findOrderByUserId/1
@Bean
@ConditionalOnEnabledGlobalFilter
public RouteToRequestUrlFilter routeToRequestUrlFilter() {return new RouteToRequestUrlFilter();
}

GateWayAutoConfiguration配置的主要bean

类名	说明
GatewayProperties	gateway属性配置类
PropertiesRouteDefinitionLocator	操作GatewayProperties对象，返回Flux<RouteDefinition>
RouteDefinitionRouteLocator	将RouteDefinition转换为Route
RoutePredicateHandlerMapping	Gateway的HandlerMapping，匹配请求对应的Route，返回FilteringWebHandler
XXXRoutePredicateFactory	路由断言工厂的bean
XXXGatewayFilterFactory	局部Filter
GlobalFilter实现类	全局Filter

DispatcherHandler

DispatcherHandler#handle作为我们查看Gateway源码的入口

• 请求request和响应response实例会被封装为ServerWebExchange
• 核心方法就是return语句

@Override
public Mono<Void> handle(ServerWebExchange exchange) {if (this.handlerMappings == null) {return createNotFoundError();}if (CorsUtils.isPreFlightRequest(exchange.getRequest())) {return handlePreFlight(exchange);}return Flux.fromIterable(this.handlerMappings) // 遍历所有的HandlerMapper.concatMap(mapping -> mapping.getHandler(exchange)) // 调用每一个HandlerMapper，能否找到Handler.next() // 继续遍历下一个HandlerMapper.switchIfEmpty(createNotFoundError()) // 如果HandlerMapper遍历完后都没有Handler，那么要抛异常了.onErrorResume(ex -> handleDispatchError(exchange, ex)).flatMap(handler -> handleRequestWith(exchange, handler)); // 如果找到Handler，那就去通过HandlerAdapter去调用Handler
}

fromIterable()方法的作用就是就是遍历Gateway所有的HandlerMapper，我们这里肯定最终是使用的RoutePredicateHandlerMapping这个路由断言的

我们接下来继续往下，遍历各个HandlerMapper，并调用mapping.getHandler(exchange)方法，这里最终会调用至RoutePredicateHandlerMapping类的getHandlerInternal()方法中，经过断言匹配后，返回一个FilteringWebHandler对象。该方法接下来会详细介绍。

中间这几行其实主要就是如果我当前往Gateway的请求，通过路由断言没有匹配上，那么就会抛异常

.next()
.switchIfEmpty(createNotFoundError())
.onErrorResume(ex -> handleDispatchError(exchange, ex))

经过路由断言匹配，得到一个WebHandler对象之后，会执行handleRequestWith(exchange, handler)方法，在该方法中会找一个与WebHandler匹配的HandlerAdapter来适配WebHandler对象，最终去调用WebHandler的

getHandler()

通过DispatcherHandler#handle方法中的.concatMap(mapping -> mapping.getHandler(exchange)) 这一行代码

进入到了AbstractHandlerMapping#getHandler：

• 遍历我们yml配置文件中所有定义的路由

• 根据我们路由定义的断言Predicate规则去调用对应的断言工厂

• 将匹配成功的路由保存至exchange对象中

  exchange.getAttributes().put(GATEWAY_ROUTE_ATTR, r);
  exchange.getAttributes().put(GATEWAY_PREDICATE_MATCHED_PATH_ROUTE_ID_ATTR, routeId);

• 断言匹配成功就返回一个WebHandler接口的实现类FilteringWebHandler对象

public Mono<Object> getHandler(ServerWebExchange exchange) {// 从这里我们就可以发现，通过getHandlerInternal(exchange)方法就能找Handler，之后的.map()方法中就直接return handler;return getHandlerInternal(exchange).map(handler -> {if (logger.isDebugEnabled()) {logger.debug(exchange.getLogPrefix() + "Mapped to " + handler);}ServerHttpRequest request = exchange.getRequest();// 正常情况下这个if都不会进入if (hasCorsConfigurationSource(handler) || CorsUtils.isPreFlightRequest(request)) {CorsConfiguration config = (this.corsConfigurationSource != null ?this.corsConfigurationSource.getCorsConfiguration(exchange) : null);CorsConfiguration handlerConfig = getCorsConfiguration(handler, exchange);config = (config != null ? config.combine(handlerConfig) : handlerConfig);if (config != null) {config.validateAllowCredentials();}if (!this.corsProcessor.process(config, exchange) || CorsUtils.isPreFlightRequest(request)) {return NO_OP_HANDLER;}}// 直接返回handlerreturn handler;});
}

我们这里就直接进入到RoutePredicateHandlerMapping类中

RoutePredicateHandlerMapping#getHandlerInternal的详细代码如下

protected Mono<?> getHandlerInternal(ServerWebExchange exchange) {if (this.managementPortType == DIFFERENT && this.managementPort != null&& exchange.getRequest().getURI().getPort() == this.managementPort) {return Mono.empty();}exchange.getAttributes().put(GATEWAY_HANDLER_MAPPER_ATTR, getSimpleName());return Mono.deferContextual(contextView -> {exchange.getAttributes().put(GATEWAY_REACTOR_CONTEXT_ATTR, contextView);// 核心方法是lookupRoute(exchange)，这里会去进行路由的校验，根据我们配置文件中定义的路由断言规则进行校验return lookupRoute(exchange).flatMap((Function<Route, Mono<?>>) r -> {// 下面几行代码就是操作exchange的属性// 上方的lookupRoute()方法中会添加GATEWAY_PREDICATE_ROUTE_ATTR，这里就进行移除exchange.getAttributes().remove(GATEWAY_PREDICATE_ROUTE_ATTR);// 把当前路由对象添加进exchange对象中，之后的流程还会用到我们的路由对象exchange.getAttributes().put(GATEWAY_ROUTE_ATTR, r);// 路由匹配成功，就直接返回WebHandler对象return Mono.just(webHandler);}).switchIfEmpty(Mono.empty().then(Mono.fromRunnable(() -> {// 当前请求没有任何一个路由匹配上的处理流程exchange.getAttributes().remove(GATEWAY_PREDICATE_ROUTE_ATTR);if (logger.isTraceEnabled()) {logger.trace("No RouteDefinition found for [" + getExchangeDesc(exchange) + "]");}})));});
}

再进入到RoutePredicateHandlerMapping#lookupRoute方法中

protected Mono<Route> lookupRoute(ServerWebExchange exchange) {// 获取到我们yml配置文件中所有定义的路由，并进行遍历return this.routeLocator.getRoutes().concatMap(route -> Mono.just(route).filterWhen(r -> {// 添加GATEWAY_PREDICATE_ROUTE_ATTRexchange.getAttributes().put(GATEWAY_PREDICATE_ROUTE_ATTR, r.getId());// 调用当前路由对象中的断言的apply()方法，apply()方法中又是一些异步的处理流程// 这里就会根据我们配置文件中为路由配置的各个断言，去调用各个断言对象return r.getPredicate().apply(exchange);}).doOnError(e -> logger.error("Error applying predicate for route: " + route.getId(), e)).onErrorResume(e -> Mono.empty())).next()// TODO: error handling.map(route -> {if (logger.isDebugEnabled()) {logger.debug("Route matched: " + route.getId());}validateRoute(route, exchange);return route;});
}

我当前gateway的配置文件中定义了两个路由

spring:cloud:gateway:#设置路由：路由id、路由到微服务的uri、断言routes:- id: user_route   #路由ID，全局唯一uri: lb://mall-user  #lb 整合负载均衡器ribbon,loadbalancerpredicates:- Path=/user/**   # 断言，路径相匹配的进行路由- id: order_route  #路由ID，全局唯一# 测试 http://localhost:8888/order/findOrderByUserId/1uri: lb://mall-order  #lb 整合负载均衡器loadbalancerpredicates:- Path=/order/**   # 断言，路径相匹配的进行路由

所以上面的方法会执行两次

因为return r.getPredicate().apply(exchange);又是一些异步调用，但我们从方法名就能看出来，这里根据我们yml配置文件中路由定义的断言去调用对应的断言对象。这就是各个断言工厂具体的实现了，接下来就以Path路径匹配的断言工厂来举例

class DefaultAsyncPredicate<T> implements AsyncPredicate<T> {private final Predicate<T> delegate;@Overridepublic Publisher<Boolean> apply(T t) { // 调用各个Predicate对象的test()方法return Mono.just(delegate.test(t));}//...
}

所以我们现在就直接去看path路径匹配的断言类PathRoutePredicateFactory，

@Override
public Predicate<ServerWebExchange> apply(Config config) {final ArrayList<PathPattern> pathPatterns = new ArrayList<>();synchronized (this.pathPatternParser) {pathPatternParser.setMatchOptionalTrailingSeparator(config.isMatchTrailingSlash());config.getPatterns().forEach(pattern -> {PathPattern pathPattern = this.pathPatternParser.parse(pattern);pathPatterns.add(pathPattern);});}return new GatewayPredicate() {// 会进入到test()方法中@Overridepublic boolean test(ServerWebExchange exchange) {// 当前请求的uri路径  /order/findOrderByUserId/1PathContainer path = parsePath(exchange.getRequest().getURI().getRawPath());PathPattern match = null;for (int i = 0; i < pathPatterns.size(); i++) {// yml配置文件中的配置项  /order/**PathPattern pathPattern = pathPatterns.get(i);// 如果path匹配成功，那么match对象就不为nullif (pathPattern.matches(path)) {match = pathPattern;break;}}// 如果path匹配成功，那么match对象就不为null  。匹配成功的处理逻辑if (match != null) {traceMatch("Pattern", match.getPatternString(), path, true);PathMatchInfo pathMatchInfo = match.matchAndExtract(path);putUriTemplateVariables(exchange, pathMatchInfo.getUriVariables());//  match.getPatternString() 为   /order/**exchange.getAttributes().put(GATEWAY_PREDICATE_MATCHED_PATH_ATTR, match.getPatternString());String routeId = (String) exchange.getAttributes().get(GATEWAY_PREDICATE_ROUTE_ATTR);// 保存当前路由idif (routeId != null) {exchange.getAttributes().put(GATEWAY_PREDICATE_MATCHED_PATH_ROUTE_ID_ATTR, routeId);}return true;}// path匹配不成，返回falseelse {traceMatch("Pattern", config.getPatterns(), path, false);return false;}}@Overridepublic Object getConfig() {return config;}@Overridepublic String toString() {return String.format("Paths: %s, match trailing slash: %b", config.getPatterns(),config.isMatchTrailingSlash());}};
}

handleRequestWith()

// DispatcherHandler#handleRequestWith
private Mono<Void> handleRequestWith(ServerWebExchange exchange, Object handler) {if (ObjectUtils.nullSafeEquals(exchange.getResponse().getStatusCode(), HttpStatus.FORBIDDEN)) {return Mono.empty();  // CORS rejection}if (this.handlerAdapters != null) {// 遍历所有的HandlerAdapterfor (HandlerAdapter adapter : this.handlerAdapters) {// 找能处理WebHandler类型的HandlerAdapter ， 最终找到SimpleHandlerAdapterif (adapter.supports(handler)) {return adapter.handle(exchange, handler).flatMap(result -> handleResult(exchange, result));}}}return Mono.error(new IllegalStateException("No HandlerAdapter: " + handler));
}

如下图所示，找到SimpleHandlerAdapter这个

SimpleHandlerAdapter的详细代码如下所示

public class SimpleHandlerAdapter implements HandlerAdapter {@Overridepublic boolean supports(Object handler) {return WebHandler.class.isAssignableFrom(handler.getClass());}@Overridepublic Mono<HandlerResult> handle(ServerWebExchange exchange, Object handler) {// 强转WebHandler webHandler = (WebHandler) handler;// getHandler()方法返回了一个FilteringWebHandler对象，这里就调用它的handle()方法Mono<Void> mono = webHandler.handle(exchange);// 返回一个空对象return mono.then(Mono.empty());}}

FilteringWebHandler#handle方法

@Override
public Mono<Void> handle(ServerWebExchange exchange) {// getHandler()方法中存入了Route路由对象，这里取出来，该对象保存着我们yml配置文件中的配置Route route = exchange.getRequiredAttribute(GATEWAY_ROUTE_ATTR);// 取出我们yml配置文件中 该路由的局部Filter，我这里有三个，一个添加请求头、一个添加请求参数、一个自定义的List<GatewayFilter> gatewayFilters = route.getFilters();// 全局FilterList<GatewayFilter> combined = new ArrayList<>(this.globalFilters);// 将局部Filter和全局Filter存入一个集合中combined.addAll(gatewayFilters);// 排序AnnotationAwareOrderComparator.sort(combined);if (logger.isDebugEnabled()) {logger.debug("Sorted gatewayFilterFactories: " + combined);}// 调用各自的filter()方法return new DefaultGatewayFilterChain(combined).filter(exchange);
}

[GatewayFilterAdapter{RemoveCachedBodyFilter@5cfed0ba}, order = -2147483648]"
[GatewayFilterAdapter{AdaptCachedBodyGlobalFilter@22a6d75c}, order = -2147482648]"
[GatewayFilterAdapter{NettyWriteResponseFilter@691567ea}, order = -1]"
[GatewayFilterAdapter{ForwardPathFilter@28be7fec}, order = 0]"
// 三个局部Filter
[[AddRequestHeader X-Request-color = 'red'], order = 1]"
[[AddRequestParameter color = 'blue'], order = 2]"
[com.tuling.mall.gateway.filter.CheckAuthGatewayFilterFactory$$Lambda$980/0x0000014b3c649390@54f513cb, order = 3]"
// 路由转换 把http://localhost:8888/order/findOrderByUserId/1  --->  lb://mall-order/order/findOrderByUserId/1
[GatewayFilterAdapter{RouteToRequestUrlFilter@5c8d58ed}, order = 10000]"
// 根据lb://前缀过滤处理，使用serviceId选择一个服务实例，从而实现负载均衡
[GatewayFilterAdapter{ReactiveLoadBalancerClientFilter@437ed416}, order = 10150]"
[GatewayFilterAdapter{LoadBalancerServiceInstanceCookieFilter@11f23038}, order = 10151]"
[GatewayFilterAdapter{WebsocketRoutingFilter@26f0141}, order = 2147483646]"
// 发送netty 请求
[GatewayFilterAdapter{NettyRoutingFilter@de77146}, order = 2147483647]"
[GatewayFilterAdapter{ForwardRoutingFilter@6a567f7b}, order = 2147483647]"

接下来就挑几个重要的全局GlobalFilter来分析

RouteToRequestUrlFilter

路由转换 把http://localhost:8888/order/findOrderByUserId/1?color=blue —> lb://mall-order/order/findOrderByUserId/1?color=blue

@Override
public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {// 从exchange中取路由Route对象Route route = exchange.getAttribute(GATEWAY_ROUTE_ATTR);if (route == null) {return chain.filter(exchange);}log.trace("RouteToRequestUrlFilter start");// 取当前请求uri ： http://localhost:8888/order/findOrderByUserId/1?color=blueURI uri = exchange.getRequest().getURI();boolean encoded = containsEncodedParts(uri);// 路由对象中保存的uri，也就是我们在yml文件中配置的值：   lb://mall-orderURI routeUri = route.getUri();if (hasAnotherScheme(routeUri)) {exchange.getAttributes().put(GATEWAY_SCHEME_PREFIX_ATTR, routeUri.getScheme());routeUri = URI.create(routeUri.getSchemeSpecificPart());}// 如果我们在yml文件中配置的uri，即不是lb开头并且host还为null，那么就抛异常if ("lb".equalsIgnoreCase(routeUri.getScheme()) && routeUri.getHost() == null) {throw new IllegalStateException("Invalid host: " + routeUri.toString());}// 转换结果为：  lb://mall-order/order/findOrderByUserId/1?color=blueURI mergedUrl = UriComponentsBuilder.fromUri(uri).scheme(routeUri.getScheme()).host(routeUri.getHost()).port(routeUri.getPort()).build(encoded).toUri();// 存入exchange中，之后的LoadBalancer全局Filter中会用到exchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, mergedUrl);return chain.filter(exchange);
}

ReactiveLoadBalancerClientFilter

解析lb://服务名，去服务注册中心获取服务实例instance，并通过负载均衡算法选择一个具体的instance

public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {// 此时的url是这个样子：   lb://mall-order/order/findOrderByUserId/1?color=blueURI url = exchange.getAttribute(GATEWAY_REQUEST_URL_ATTR);String schemePrefix = exchange.getAttribute(GATEWAY_SCHEME_PREFIX_ATTR);if (url == null || (!"lb".equals(url.getScheme()) && !"lb".equals(schemePrefix))) {return chain.filter(exchange);}addOriginalRequestUrl(exchange, url);if (log.isTraceEnabled()) {log.trace(ReactiveLoadBalancerClientFilter.class.getSimpleName() + " url before: " + url);}// 再获取一遍：lb://mall-order/order/findOrderByUserId/1?color=blueURI requestUri = exchange.getAttribute(GATEWAY_REQUEST_URL_ATTR);// 就是服务名：    mall-orderString serviceId = requestUri.getHost();Set<LoadBalancerLifecycle> supportedLifecycleProcessors = LoadBalancerLifecycleValidator.getSupportedLifecycleProcessors(clientFactory.getInstances(serviceId, LoadBalancerLifecycle.class),RequestDataContext.class, ResponseData.class, ServiceInstance.class);// 请求信息 封装成一个对象DefaultRequest<RequestDataContext> lbRequest = new DefaultRequest<>(new RequestDataContext(new RequestData(exchange.getRequest()), getHint(serviceId)));// 调用choose()方法return choose(lbRequest, serviceId, supportedLifecycleProcessors).doOnNext(response -> {// 服务注册中心的响应response，获取server实例对象ServiceInstance retrievedInstance = response.getServer();// 值为http://localhost:8888/order/findOrderByUserId/1?color=blueURI uri = exchange.getRequest().getURI();String overrideScheme = retrievedInstance.isSecure() ? "https" : "http";if (schemePrefix != null) {overrideScheme = url.getScheme();}// 服务实例DelegatingServiceInstance serviceInstance = new DelegatingServiceInstance(retrievedInstance,overrideScheme);// 最终通过上面的服务实例，修改之后的请求url为：http://192.168.236.173:8020/order/findOrderByUserId/1?color=blueURI requestUrl = reconstructURI(serviceInstance, uri);if (log.isTraceEnabled()) {log.trace("LoadBalancerClientFilter url chosen: " + requestUrl);}// 存入exchange对象中，之后netty发送请求会用到该urlexchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, requestUrl);exchange.getAttributes().put(GATEWAY_LOADBALANCER_RESPONSE_ATTR, response);supportedLifecycleProcessors.forEach(lifecycle -> lifecycle.onStartRequest(lbRequest, response));}).then(chain.filter(exchange)).doOnError(throwable -> supportedLifecycleProcessors.forEach(lifecycle -> lifecycle.onComplete(new CompletionContext<ResponseData, ServiceInstance, RequestDataContext>(CompletionContext.Status.FAILED, throwable, lbRequest,exchange.getAttribute(GATEWAY_LOADBALANCER_RESPONSE_ATTR))))).doOnSuccess(aVoid -> supportedLifecycleProcessors.forEach(lifecycle -> lifecycle.onComplete(new CompletionContext<ResponseData, ServiceInstance, RequestDataContext>(CompletionContext.Status.SUCCESS, lbRequest,exchange.getAttribute(GATEWAY_LOADBALANCER_RESPONSE_ATTR),new ResponseData(exchange.getResponse(), new RequestData(exchange.getRequest()))))));
}// 进入到choose()方法中
private Mono<Response<ServiceInstance>> choose(Request<RequestDataContext> lbRequest, String serviceId,Set<LoadBalancerLifecycle> supportedLifecycleProcessors) {ReactorLoadBalancer<ServiceInstance> loadBalancer = this.clientFactory.getInstance(serviceId,ReactorServiceInstanceLoadBalancer.class);if (loadBalancer == null) {throw new NotFoundException("No loadbalancer available for " + serviceId);}supportedLifecycleProcessors.forEach(lifecycle -> lifecycle.onStart(lbRequest));// 调用ReactorLoadBalancer对象的choose()方法return loadBalancer.choose(lbRequest);
}

NettyRoutingFilter

发送netty请求

public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {// 经过负载均衡之后的请求url，具体的下游服务请求地址// http://192.168.236.173:8020/order/findOrderByUserId/1?color=blueURI requestUrl = exchange.getRequiredAttribute(GATEWAY_REQUEST_URL_ATTR);// scheme为httpString scheme = requestUrl.getScheme();if (isAlreadyRouted(exchange) || (!"http".equalsIgnoreCase(scheme) && !"https".equalsIgnoreCase(scheme))) {return chain.filter(exchange);}setAlreadyRouted(exchange);ServerHttpRequest request = exchange.getRequest();// GET 请求final HttpMethod method = HttpMethod.valueOf(request.getMethod().name());// url为 http://192.168.236.173:8020/order/findOrderByUserId/1?color=bluefinal String url = requestUrl.toASCIIString();// 请求头HttpHeaders filtered = filterRequest(getHeadersFilters(), exchange);final DefaultHttpHeaders httpHeaders = new DefaultHttpHeaders();filtered.forEach(httpHeaders::set);boolean preserveHost = exchange.getAttributeOrDefault(PRESERVE_HOST_HEADER_ATTRIBUTE, false);// 路由对象Route route = exchange.getAttribute(GATEWAY_ROUTE_ATTR);Flux<HttpClientResponse> responseFlux = getHttpClient(route, exchange).headers(headers -> {headers.add(httpHeaders);// Will either be set below, or later by Nettyheaders.remove(HttpHeaders.HOST);if (preserveHost) {String host = request.getHeaders().getFirst(HttpHeaders.HOST);headers.add(HttpHeaders.HOST, host);}// 发送请求}).request(method).uri(url).send((req, nettyOutbound) -> {if (log.isTraceEnabled()) {nettyOutbound.withConnection(connection -> log.trace(...);}return nettyOutbound.send(request.getBody().map(this::getByteBuf));}).responseConnection((res, connection) -> {// Defer committing the response until all route filters have run// Put client response as ServerWebExchange attribute and write// response later NettyWriteResponseFilterexchange.getAttributes().put(CLIENT_RESPONSE_ATTR, res);exchange.getAttributes().put(CLIENT_RESPONSE_CONN_ATTR, connection);ServerHttpResponse response = exchange.getResponse();// put headers and status so filters can modify the responseHttpHeaders headers = new HttpHeaders();res.responseHeaders().forEach(entry -> headers.add(entry.getKey(), entry.getValue()));String contentTypeValue = headers.getFirst(HttpHeaders.CONTENT_TYPE);if (StringUtils.hasLength(contentTypeValue)) {exchange.getAttributes().put(ORIGINAL_RESPONSE_CONTENT_TYPE_ATTR, contentTypeValue);}setResponseStatus(res, response);// make sure headers filters run after setting status so it is// available in responseHttpHeaders filteredResponseHeaders = HttpHeadersFilter.filter(getHeadersFilters(), headers, exchange,Type.RESPONSE);if (!filteredResponseHeaders.containsKey(HttpHeaders.TRANSFER_ENCODING)&& filteredResponseHeaders.containsKey(HttpHeaders.CONTENT_LENGTH)) {// It is not valid to have both the transfer-encoding header and// the content-length header.// Remove the transfer-encoding header in the response if the// content-length header is present.response.getHeaders().remove(HttpHeaders.TRANSFER_ENCODING);}exchange.getAttributes().put(CLIENT_RESPONSE_HEADER_NAMES, filteredResponseHeaders.keySet());response.getHeaders().addAll(filteredResponseHeaders);return Mono.just(res);});Duration responseTimeout = getResponseTimeout(route);if (responseTimeout != null) {responseFlux = responseFlux.timeout(responseTimeout,Mono.error(new TimeoutException("Response took longer than timeout: " + responseTimeout))).onErrorMap(TimeoutException.class,th -> new ResponseStatusException(HttpStatus.GATEWAY_TIMEOUT, th.getMessage(), th));}return responseFlux.then(chain.filter(exchange));
}

补充知识

适配器模式

在FilteringWebHandler#handle方法中，先获取路由的局部Filter，在创建一个集合存放全局Filter，在把局部Filter和全局Filter放在一起。这里就有一个问题：

局部Filter的类型是GatewayFilter，而全局Filter的类型是GlobalFilter，它们是怎么通过下面这种方式存放在一个集合中的嘞？

// 局部Filter
List<GatewayFilter> gatewayFilters = route.getFilters();
// 全局Filter
List<GatewayFilter> combined = new ArrayList<>(this.globalFilters);
// 将局部Filter和全局Filter存入一个集合中
combined.addAll(gatewayFilters);

这里就用到了适配器模式，具体实现步骤是：

• 创建一个GatewayFilterAdapter类，实现 GatewayFilter接口
• GatewayFilterAdapter类中定义一个GlobalFilter属性，构造方法中传GlobalFilter类型的对象赋值给该属性
• 实现GatewayFilter接口的filter()方法，在filter()方法中调用全局Filter的filter()方法

private static class GatewayFilterAdapter implements GatewayFilter {private final GlobalFilter delegate;GatewayFilterAdapter(GlobalFilter delegate) {this.delegate = delegate;}@Overridepublic Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {return this.delegate.filter(exchange, chain);}
}

遍历List<GlobalFilter> globalFilters全局Filter，分别存入GatewayFilterAdapter对象中

List<GatewayFilterAdapter> ----> List<GatewayFilter> globalFilters集合

@Override
public Mono<Void> handle(ServerWebExchange exchange) {Route route = exchange.getRequiredAttribute(GATEWAY_ROUTE_ATTR);// 局部FilterList<GatewayFilter> gatewayFilters = route.getFilters();// 全局Filter，这样就把全局GlobalFilter变为了GatewayFilter类型了List<GatewayFilter> combined = new ArrayList<>(this.globalFilters);// 存入一个集合中combined.addAll(gatewayFilters);AnnotationAwareOrderComparator.sort(combined);// 调用各自的filter()方法return new DefaultGatewayFilterChain(combined).filter(exchange);
}

详细流程图