gateway - 启动

咱们从spring.factories开始，主要是GatewayAutoConfiguration，这里主要加载CompositeRouteDefinitionLocator、RouteDefinitionRouteLocator、FilteringWebHandler、RoutePredicateHandlerMapping、RouteRefreshListener、CachingRouteLocator等。
RouteLocator和RouteDefinitionLocator的做用在上一篇已经提过了，FilteringWebHandler、RoutePredicateHandlerMapping这两个等调用的时候讲，这边先知道他们会在这里加载。咱们主要看看RouteRefreshListener和CachingRouteLocator。

RouteRefreshListener

RouteRefreshListener实现了ApplicationListener接口，因此他会调用onApplicationEvent方法，在符合某些条件下，会调用reset方法，这个思路和zuul是同样的。因此动态的刷新也能够调用他的事件来触发。

public void onApplicationEvent(ApplicationEvent event) {
    if (event instanceof ContextRefreshedEvent
            || event instanceof RefreshScopeRefreshedEvent
            || event instanceof InstanceRegisteredEvent) {
        reset();
    }
    else if (event instanceof ParentHeartbeatEvent) {
        ParentHeartbeatEvent e = (ParentHeartbeatEvent) event;
        resetIfNeeded(e.getValue());
    }
    else if (event instanceof HeartbeatEvent) {
        HeartbeatEvent e = (HeartbeatEvent) event;
        resetIfNeeded(e.getValue());
    }
}

咱们看看reset方法，他其实就是发布了一个RefreshRoutesEvent事件。

private void reset() {
    this.publisher.publishEvent(new RefreshRoutesEvent(this));
}

CachingRouteLocator

CachingRouteLocator就是用来接收RefreshRoutesEvent事件的，他实现了ApplicationListener<RefreshRoutesEvent>接口。咱们看看他的onApplicationEvent方法。

public void onApplicationEvent(RefreshRoutesEvent event) {
    try {
        fetch().collect(Collectors.toList()).subscribe(list -> Flux.fromIterable(list)
                .materialize().collect(Collectors.toList()).subscribe(signals -> {
                    applicationEventPublisher
                            .publishEvent(new RefreshRoutesResultEvent(this));
                    cache.put(CACHE_KEY, signals);
                }, throwable -> handleRefreshError(throwable)));
    }
    catch (Throwable e) {
        handleRefreshError(e);
    }
}

他先会调用fetch方法，这里实际上就是调用CompositeRouteLocator#getRoutes，最后再调用RouteDefinitionRouteLocator#getRoutes。

private Flux<Route> fetch() {
    return this.delegate.getRoutes().sort(AnnotationAwareOrderComparator.INSTANCE);
}

RouteDefinitionRouteLocator#getRoutes

这个方法能够看到他是获取RouteDefinition的集合，而后再调用convertToRoute方法，在这个方法里，把RouteDefinition转为Route。

@Override
public Flux<Route> getRoutes() {
    Flux<Route> routes = this.routeDefinitionLocator.getRouteDefinitions()
            .map(this::convertToRoute);

    // 其余略
}

RouteDefinitionRouteLocator#convertToRoute

在这里把RouteDefinition转为Route，主要是解析Predicate和GatewayFilter，咱们在上一篇已经知道了他会经过工厂类来处理。combinePredicates方法就是处理Predicate的，getFilters是处理Filter的。

private Route convertToRoute(RouteDefinition routeDefinition) {
    AsyncPredicate<ServerWebExchange> predicate = combinePredicates(routeDefinition);
    List<GatewayFilter> gatewayFilters = getFilters(routeDefinition);

    return Route.async(routeDefinition).asyncPredicate(predicate)
            .replaceFilters(gatewayFilters).build();
}

RouteDefinitionRouteLocator#combinePredicates

在这里就是把RouteDefinition的predicate转为Route须要的Predicate。这里首先会建立一个Predicate，而后再把剩余的合并，造成了一个left、right的结构。结构图在上一篇已经说过了。
lookup方法就是经过工厂类建立Predicate的地方。

private AsyncPredicate<ServerWebExchange> combinePredicates(
        RouteDefinition routeDefinition) {
    List<PredicateDefinition> predicates = routeDefinition.getPredicates();
    if (predicates == null || predicates.isEmpty()) {
        // this is a very rare case, but possible, just match all
        return AsyncPredicate.from(exchange -> true);
    }
    // 建立第一个Predicate
    AsyncPredicate<ServerWebExchange> predicate = lookup(routeDefinition,
            predicates.get(0));
    // 把剩余的进行合并
    for (PredicateDefinition andPredicate : predicates.subList(1,
            predicates.size())) {
        AsyncPredicate<ServerWebExchange> found = lookup(routeDefinition,
                andPredicate);
        predicate = predicate.and(found);
    }

    return predicate;
}

RouteDefinitionRouteLocator#lookup

这个方法里，首先先经过配置的名称，获取对应的RoutePredicateFactory，而后组装config信息，最后经过factory.applyAsync建立Predicate。

private AsyncPredicate<ServerWebExchange> lookup(RouteDefinition route,
        PredicateDefinition predicate) {
    RoutePredicateFactory<Object> factory = this.predicates.get(predicate.getName());
    if (factory == null) {
        throw new IllegalArgumentException(
                "Unable to find RoutePredicateFactory with name "
                        + predicate.getName());
    }
    if (logger.isDebugEnabled()) {
        logger.debug("RouteDefinition " + route.getId() + " applying "
                + predicate.getArgs() + " to " + predicate.getName());
    }

    // @formatter:off
    Object config = this.configurationService.with(factory)
            .name(predicate.getName())
            .properties(predicate.getArgs())
            .eventFunction((bound, properties) -> new PredicateArgsEvent(
                    RouteDefinitionRouteLocator.this, route.getId(), properties))
            .bind();
    // @formatter:on

    return factory.applyAsync(config);
}

RouteDefinitionRouteLocator#getFilters

这个是处理Filter的地方，他主要是经过loadGatewayFilters方法来获取对应的Filter。

private List<GatewayFilter> getFilters(RouteDefinition routeDefinition) {
    List<GatewayFilter> filters = new ArrayList<>();

    // TODO: support option to apply defaults after route specific filters?
    if (!this.gatewayProperties.getDefaultFilters().isEmpty()) {
        filters.addAll(loadGatewayFilters(DEFAULT_FILTERS,
                new ArrayList<>(this.gatewayProperties.getDefaultFilters())));
    }

    if (!routeDefinition.getFilters().isEmpty()) {
        filters.addAll(loadGatewayFilters(routeDefinition.getId(),
                new ArrayList<>(routeDefinition.getFilters())));
    }

    AnnotationAwareOrderComparator.sort(filters);
    return filters;
}

RouteDefinitionRouteLocator#loadGatewayFilters

这个设计方式跟上面相似，也是经过配置信息的名称，获取对应的GatewayFilterFactory，而后封装configuration信息，经过factory.apply建立一个Filter。

List<GatewayFilter> loadGatewayFilters(String id,
        List<FilterDefinition> filterDefinitions) {
    ArrayList<GatewayFilter> ordered = new ArrayList<>(filterDefinitions.size());
    for (int i = 0; i < filterDefinitions.size(); i++) {
        FilterDefinition definition = filterDefinitions.get(i);
        GatewayFilterFactory factory = this.gatewayFilterFactories
                .get(definition.getName());
        if (factory == null) {
            throw new IllegalArgumentException(
                    "Unable to find GatewayFilterFactory with name "
                            + definition.getName());
        }
        if (logger.isDebugEnabled()) {
            logger.debug("RouteDefinition " + id + " applying filter "
                    + definition.getArgs() + " to " + definition.getName());
        }

        // @formatter:off
        Object configuration = this.configurationService.with(factory)
                .name(definition.getName())
                .properties(definition.getArgs())
                .eventFunction((bound, properties) -> new FilterArgsEvent(
                        // TODO: why explicit cast needed or java compile fails
                        RouteDefinitionRouteLocator.this, id, (Map<String, Object>) properties))
                .bind();
        // @formatter:on

        // some filters require routeId
        // TODO: is there a better place to apply this?
        if (configuration instanceof HasRouteId) {
            HasRouteId hasRouteId = (HasRouteId) configuration;
            hasRouteId.setRouteId(id);
        }

        GatewayFilter gatewayFilter = factory.apply(configuration);
        if (gatewayFilter instanceof Ordered) {
            ordered.add(gatewayFilter);
        }
        else {
            ordered.add(new OrderedGatewayFilter(gatewayFilter, i + 1));
        }
    }

    return ordered;
}

总体流程