api網關揭秘--spring cloud gateway源碼解析

要想了解spring cloud gateway的源碼，要熟悉spring webflux，我的上篇文章介紹了spring webflux。

1.gateway 和zuul對比

I am the author of spring cloud gateway. Zuul is built on servlet 2.5 (works with 3.x), using blocking APIs. It doesn't support any long lived connections, like websockets.

Gateway is built on Spring Framework 5, Project Reactor and Spring Boot 2 using non-blocking APIs. Websockets are supported and it's a much better developer experience since it's tightly integrated with Spring.

簡單的來說：

　　1.zuul是基於servlet 2.5，兼容servlet3.0，使用的是阻塞API，不支持長連接如websocket

　　2.Gateway基於spring5，Reactor和Spring boot2使用了非阻塞API，支持websocket，和spring完美集成，對開發者友好。

　　另外

　　3.zuul2支持非阻塞API，但沒有和spring cloud集成，且已經停止維護，不在考慮之列。

2.架構圖

3.自動配置解析core spring.factories

# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.cloud.gateway.config.GatewayClassPathWarningAutoConfiguration,\
org.springframework.cloud.gateway.config.GatewayAutoConfiguration,\
org.springframework.cloud.gateway.config.GatewayLoadBalancerClientAutoConfiguration,\
org.springframework.cloud.gateway.config.GatewayNoLoadBalancerClientAutoConfiguration,\
org.springframework.cloud.gateway.config.GatewayMetricsAutoConfiguration,\
org.springframework.cloud.gateway.config.GatewayRedisAutoConfiguration,\
org.springframework.cloud.gateway.discovery.GatewayDiscoveryClientAutoConfiguration
org.springframework.boot.env.EnvironmentPostProcessor=\
org.springframework.cloud.gateway.config.GatewayEnvironmentPostProcessor

3.1 GatewayClassPathWarningAutoConfiguration檢查前端控制器

    @Configuration
    @ConditionalOnClass(name = "org.springframework.web.servlet.DispatcherServlet")
    protected static class SpringMvcFoundOnClasspathConfiguration {

        public SpringMvcFoundOnClasspathConfiguration() {
            log.warn(BORDER
                    + "Spring MVC found on classpath, which is incompatible with Spring Cloud Gateway at this time. "
                    + "Please remove spring-boot-starter-web dependency." + BORDER);
        }

    }

    @Configuration
    @ConditionalOnMissingClass("org.springframework.web.reactive.DispatcherHandler")
    protected static class WebfluxMissingFromClasspathConfiguration {

        public WebfluxMissingFromClasspathConfiguration() {
            log.warn(BORDER + "Spring Webflux is missing from the classpath, "
                    + "which is required for Spring Cloud Gateway at this time. "
                    + "Please add spring-boot-starter-webflux dependency." + BORDER);
        }

    }

1.若存在springmvc的前端控制器org.springframework.web.servlet.DispatcherServlet，則報警,原因是使用非阻塞的API

2.若不存在spring webflux的前端控制器org.springframework.web.reactive.DispatcherHandler，則報警,原因是需要使用非阻塞的API

3.2 網關自動配置GatewayAutoConfiguration

3.2.1 RoutePredicateHandlerMapping

    @Bean
    public RoutePredicateHandlerMapping routePredicateHandlerMapping(
            FilteringWebHandler webHandler, RouteLocator routeLocator,
            GlobalCorsProperties globalCorsProperties, Environment environment) {
        return new RoutePredicateHandlerMapping(webHandler, routeLocator,
                globalCorsProperties, environment);
    }

RoutePredicateHandlerMapping繼承自AbstractHandlerMapping，在此步進行路徑查找

    @Override
    protected Mono<?> getHandlerInternal(ServerWebExchange exchange) {
        // don't handle requests on the management port if set
        if (managmentPort != null
                && exchange.getRequest().getURI().getPort() == managmentPort.intValue()) {
            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); //2 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) + "]");
                    }
                })));
    }

protected Mono<Route> lookupRoute(ServerWebExchange exchange) {//1
        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()); }
         */
    }

 1.通過RouteLocator返回Route

 

 關於Route的定義

    private Route(String id, URI uri, int order,
            AsyncPredicate<ServerWebExchange> predicate,
            List<GatewayFilter> gatewayFilters) {
        this.id = id;
        this.uri = uri;
        this.order = order;
        this.predicate = predicate;
        this.gatewayFilters = gatewayFilters;
    }

可以看出url和gatewayFilter進行了綁定

 2.將Route放入ServerWebExchange的屬性中。

3.2.2 FilteringWebHandler

    @Bean
    public FilteringWebHandler filteringWebHandler(List<GlobalFilter> globalFilters) {
        return new FilteringWebHandler(globalFilters);
    }

 

 

參考文獻：

【1】https://stackoverflow.com/questions/47092048/how-spring-cloud-gateway-is-different-from-zuul

【2】https://blog.csdn.net/xuejike/article/details/81290695