配置文件配置

spring:
  cloud:
    gateway:
      routes:
      - id: fiction-server
        uri: lb://xd-fiction-server
        predicates:
            - Path=/book/**  # 
        filters:
          - PrefixPath=/client # GatewayFilter，可以配置多个    

上面的配置会先通过 PathRoutePredicateFactory 查到 小说服务。然后通过PrefixPath 查找 小说服务的 /client/book/** 接口

各个接口简单说明

Predicate

gateway的入口类，主要是通过头信息，参数，时间和路径查找对应的服务

GatewayFilter

配置在配置文件的filter的的接口类。

GlobalFilter

全局过滤器，默认所有的route都会通过该过滤器执行，一般实现该接口都会实现 orderd 接口，过滤器的执行顺序需要通过order去判断先后顺序，需要是指责链模式,具体可以查找FilteringWebHandler，改类给出了详细的实现方式，GlobalFilter和GatewayFilter虽然继承不同的接口，其实最终还是同一个地方用到。

FilteringWebHandler

过滤器执行,把全局过滤器和局部过滤器按照orderd顺序排序执行。

RoutePredicateHandlerMapping

gateway的核心执行类，

先通过Predicate查找对应的router

protected Mono<Route> lookupRoute(ServerWebExchange exchange) {
	return this.routeLocator.getRoutes()
			// individually filter routes so that filterWhen error delaying is not a
			// problem
			.concatMap(route -> Mono.just(route).filterWhen(r -> {
				// add the current route we are testing
				exchange.getAttributes().put(GATEWAY_PREDICATE_ROUTE_ATTR, r.getId());
				return r.getPredicate().apply(exchange);
			})
					// instead of immediately stopping main flux due to error, log and
					// swallow it
					.doOnError(e -> logger.error(
							"Error applying predicate for route: " + route.getId(),
							e))
					.onErrorResume(e -> Mono.empty()))
			// .defaultIfEmpty() put a static Route not found
			// or .switchIfEmpty()
			// .switchIfEmpty(Mono.<Route>empty().log("noroute"))
			.next()
			// TODO: error handling
			.map(route -> {
				if (logger.isDebugEnabled()) {
					logger.debug("Route matched: " + route.getId());
				}
				validateRoute(route, exchange);
				return route;
			});

	/*
	 * TODO: trace logging if (logger.isTraceEnabled()) {
	 * logger.trace("RouteDefinition did not match: " + routeDefinition.getId()); }
	 */
}

然后通过 router查找到对应的FilteringWebHandler

protected Mono<?> getHandlerInternal(ServerWebExchange exchange) {
	// don't handle requests on management port if set and different than server port
	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 lookupRoute(exchange)
			// .log("route-predicate-handler-mapping", Level.FINER) //name this
			.flatMap((Function<Route, Mono<?>>) r -> {
				exchange.getAttributes().remove(GATEWAY_PREDICATE_ROUTE_ATTR);
				if (logger.isDebugEnabled()) {
					logger.debug(
							"Mapping [" + getExchangeDesc(exchange) + "] to " + r);
				}

				exchange.getAttributes().put(GATEWAY_ROUTE_ATTR, r);
				return Mono.just(webHandler);
			}).switchIfEmpty(Mono.empty().then(Mono.fromRunnable(() -> {
				exchange.getAttributes().remove(GATEWAY_PREDICATE_ROUTE_ATTR);
				if (logger.isTraceEnabled()) {
					logger.trace("No RouteDefinition found for ["
							+ getExchangeDesc(exchange) + "]");
				}
			})));
}

至于后面其实是基于Spring webflux做的一些事情，基本上有问题，入口类从这里找起会比较合适。

RouteDefinitionRouteLocator

路由加载器，请求的时候会加载一边数据。如果需要知道Predicate 可以加载一个还是多个，是如何加载的，可以看下里面的代码。