private static final String CACHE_KEY = "routes";

private final RouteLocator delegate;

private final Flux<Route> routes;

private final Map<String, List> cache = new ConcurrentHashMap<>();

private ApplicationEventPublisher applicationEventPublisher;

public CachingRouteLocator(RouteLocator delegate) {
    this.delegate = delegate;
    /*
     * 获取路由信息
     * 从cache中获取routes键对应的值，如果不存在，则调用fetch方法来获取
     */
    routes = CacheFlux.lookup(cache, CACHE_KEY, Route.class).onCacheMissResume(this::fetch);
}

private Flux<Route> fetch() {
    // 获取路由并排序
    return this.delegate.getRoutes().sort(AnnotationAwareOrderComparator.INSTANCE);
}

/*
 * 该bean的优先级较高，将上面routeDefinitionRouteLocator的返回值先封装为CompositeRouteLocator，
 * 然后再封装为CachingRouteLocator，
 * CompositeRouteLocator和CachingRouteLocator都是RouteLocator的另外两个特殊的实现类。
 *
 * RouteDefinitionRouteLocator在调用getRoutes时才对路由信息进行处理，
 * 所以CachingRouteLocator会在初始化时就调用每个RouterLocator的getRoutes组装好所有的route对象并进行缓存，
 * 以供RoutePredicateHandlerMapping调用。
 */
@Bean
@Primary
@ConditionalOnMissingBean(name = "cachedCompositeRouteLocator")
// TODO: property to disable composite?
public RouteLocator cachedCompositeRouteLocator(List<RouteLocator> routeLocators) {
    /*
     * 默认情况下，这里的routeLocators包含两个元素，除了上面的routeDefinitionRouteLocator方法创建的bean外，
     * 还有RouteLocatorBuilder$Builder中的lambda（暂时没找到是哪里出入这个的）。
     */
    return new CachingRouteLocator(new CompositeRouteLocator(Flux.fromIterable(routeLocators)));
}

@Override
public Flux<Route> getRoutes() {
    return this.routes;
}

public class CompositeRouteLocator implements RouteLocator {

	private final Flux<RouteLocator> delegates;

	public CompositeRouteLocator(Flux<RouteLocator> delegates) {
		this.delegates = delegates;
	}

	@Override
	public Flux<Route> getRoutes() {
		// 从多个路由定位器中获取路由信息
		return this.delegates.flatMapSequential(RouteLocator::getRoutes);
	}

	@Override
	public Flux<Route> getRoutesByMetadata(Map<String, Object> metadata) {
		return this.delegates.flatMapSequential(routeLocator -> routeLocator.getRoutesByMetadata(metadata));
	}

}

/*
 * RouteLocator是用来获取路由的，RouteDefinitionRouteLocator只是其中一个实现类，
 * 封装了RouteDefinitionLocator、GatewayFilterFactory、RoutePredicateFactory，
 * 可以看到其组合了RouteDefinitionLocator，实际上是上面的CompositeRouteDefinitionLocator类型的对象。
 * RouteDefinitionRouteLocator是指根据RouteDefinition来获取Route对象。
 */
@Bean
public RouteLocator routeDefinitionRouteLocator(GatewayProperties properties,
        List<GatewayFilterFactory> gatewayFilters, List<RoutePredicateFactory> predicates,
        RouteDefinitionLocator routeDefinitionLocator, ConfigurationService configurationService) {
    return new RouteDefinitionRouteLocator(routeDefinitionLocator, predicates, gatewayFilters, properties,
            configurationService);
}

/*
 * 该bean会封装所有的RouteDefinitionLocator，这里的bean的优先级更高。
 * 会将上面的propertiesRouteDefinitionLocator和InMemoryRouteDefinitionRepository进行封装。
 */
@Bean
@Primary
public RouteDefinitionLocator routeDefinitionLocator(List<RouteDefinitionLocator> routeDefinitionLocators) {
    // 默认情况下，这里的routeDefinitionLocators包含2个元素，分别是上面两个bean定义。
    return new CompositeRouteDefinitionLocator(Flux.fromIterable(routeDefinitionLocators));
}

/*
 * 要注意区分RouteDefinitionLocator和RouteLocator，前者是存储路由定义信息，后者是查找路由信息
 * 两者的关系参考类图：https://img-blog.csdnimg.cn/20210401131318609.png
 */

/*
 * 存储从配置文件中读取的路由信息
 * 这是个RouteDefinitionLocator
 */
@Bean
@ConditionalOnMissingBean
public PropertiesRouteDefinitionLocator propertiesRouteDefinitionLocator(GatewayProperties properties) {
    return new PropertiesRouteDefinitionLocator(properties);
}

// 这个也是个RouteDefinitionLocator
@Bean
@ConditionalOnMissingBean(RouteDefinitionRepository.class)
public InMemoryRouteDefinitionRepository inMemoryRouteDefinitionRepository() {
    return new InMemoryRouteDefinitionRepository();
}

/**
 * Default filters name.
 */
public static final String DEFAULT_FILTERS = "defaultFilters";

protected final Log logger = LogFactory.getLog(getClass());

private final RouteDefinitionLocator routeDefinitionLocator;

private final ConfigurationService configurationService;

private final Map<String, RoutePredicateFactory> predicates = new LinkedHashMap<>();

private final Map<String, GatewayFilterFactory> gatewayFilterFactories = new HashMap<>();

private final GatewayProperties gatewayProperties;

public RouteDefinitionRouteLocator(RouteDefinitionLocator routeDefinitionLocator,
        List<RoutePredicateFactory> predicates, List<GatewayFilterFactory> gatewayFilterFactories,
        GatewayProperties gatewayProperties, ConfigurationService configurationService) {
    this.routeDefinitionLocator = routeDefinitionLocator;
    this.configurationService = configurationService;
    // 初始化断言信息
    initFactories(predicates);
    // 初始化filter信息，与初始化断言信息类似
    gatewayFilterFactories.forEach(factory -> this.gatewayFilterFactories.put(factory.name(), factory));
    this.gatewayProperties = gatewayProperties;
}

private void initFactories(List<RoutePredicateFactory> predicates) {
    predicates.forEach(factory -> {
        // 这里key是RoutePredicateFactory实现类的类名称的前缀，如AfterRoutePredicateFactory则key为After
        String key = factory.name();
        if (this.predicates.containsKey(key)) {
            this.logger.warn("A RoutePredicateFactory named " + key + " already exists, class: "
                    + this.predicates.get(key) + ". It will be overwritten.");
        }
        /*
         * 如果已经存在了同一个key的predicateFactory，则覆盖掉，
         * 因为该方法只有在RouteDefinitionRouterLocator组件被初始化时才会被调用， 所以这里说明以SCG内置的断言工厂为主
         */
        this.predicates.put(key, factory);
        if (logger.isInfoEnabled()) {
            logger.info("Loaded RoutePredicateFactory [" + key + "]");
        }
    });
}

// 返回路由信息
@Override
public Flux<Route> getRoutes() {
    // 通过routeDefinitionLocator获取所有的路由定义信息
    return getRoutes(this.routeDefinitionLocator.getRouteDefinitions());
}

private Flux<Route> getRoutes(Flux<RouteDefinition> routeDefinitions) {
    // 将路由信息转为路由对象
    Flux<Route> routes = routeDefinitions.map(this::convertToRoute);

    if (!gatewayProperties.isFailOnRouteDefinitionError()) {
        // instead of letting error bubble up, continue
        routes = routes.onErrorContinue((error, obj) -> {
            if (logger.isWarnEnabled()) {
                logger.warn("RouteDefinition id " + ((RouteDefinition) obj).getId()
                        + " will be ignored. Definition has invalid configs, " + error.getMessage());
            }
        });
    }

    return routes.map(route -> {
        if (logger.isDebugEnabled()) {
            logger.debug("RouteDefinition matched: " + route.getId());
        }
        return route;
    });
}

private Route convertToRoute(RouteDefinition routeDefinition) {
    // 获取路由定义中的断言信息并组合成一个断言（如果有多个的话）
    AsyncPredicate<ServerWebExchange> predicate = combinePredicates(routeDefinition);
    // 获取路由定义中的filter
    List<GatewayFilter> gatewayFilters = getFilters(routeDefinition);
    // 构建Route对象
    return Route.async(routeDefinition).asyncPredicate(predicate).replaceFilters(gatewayFilters).build();
}

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);
    }
    AsyncPredicate<ServerWebExchange> predicate = lookup(routeDefinition, predicates.get(0));

    /*
     * 如果该路由定义了多个断言，将其用and运算连接起来
     */
    for (PredicateDefinition andPredicate : predicates.subList(1, predicates.size())) {
        // 转化为异步的断言
        AsyncPredicate<ServerWebExchange> found = lookup(routeDefinition, andPredicate);
        // 用and连接起来
        predicate = predicate.and(found);
    }

    return predicate;
}

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

    // TODO: support option to apply defaults after route specific filters?
    // 如果配置了全局默认过滤器，则添加到集合中
    if (!this.gatewayProperties.getDefaultFilters().isEmpty()) {
        filters.addAll(loadGatewayFilters(routeDefinition.getId(),
                new ArrayList<>(this.gatewayProperties.getDefaultFilters())));
    }

    // 添加路由定义中配置的过滤器
    final List<FilterDefinition> definitionFilters = routeDefinition.getFilters();
    if (!CollectionUtils.isEmpty(definitionFilters)) {
        filters.addAll(loadGatewayFilters(routeDefinition.getId(), definitionFilters));
    }

    // 对过滤器进行排序
    AnnotationAwareOrderComparator.sort(filters);
    return filters;
}

public class CompositeRouteDefinitionLocator implements RouteDefinitionLocator {

	private static final Log log = LogFactory.getLog(CompositeRouteDefinitionLocator.class);

	private final Flux<RouteDefinitionLocator> delegates;

	private final IdGenerator idGenerator;

	public CompositeRouteDefinitionLocator(Flux<RouteDefinitionLocator> delegates) {
		this(delegates, new AlternativeJdkIdGenerator());
	}

	public CompositeRouteDefinitionLocator(Flux<RouteDefinitionLocator> delegates, IdGenerator idGenerator) {
		this.delegates = delegates;
		this.idGenerator = idGenerator;
	}

	@Override
	public Flux<RouteDefinition> getRouteDefinitions() {
		// 通过委托对象来获取路由定义
		return this.delegates.flatMapSequential(RouteDefinitionLocator::getRouteDefinitions)
				.flatMap(routeDefinition -> { // 处理返回的多条路由定义
					if (routeDefinition.getId() == null) {
						// 如果路由id是null，则生成一个
						return randomId().map(id -> {
							routeDefinition.setId(id);
							if (log.isDebugEnabled()) {
								log.debug("Id set on route definition: " + routeDefinition);
							}
							return routeDefinition;
						});
					}
					return Mono.just(routeDefinition);
				});
	}

	protected Mono<String> randomId() {
		return Mono.fromSupplier(idGenerator::generateId).map(UUID::toString).publishOn(Schedulers.boundedElastic());
	}

}

public class PropertiesRouteDefinitionLocator implements RouteDefinitionLocator {

	private final GatewayProperties properties;

	public PropertiesRouteDefinitionLocator(GatewayProperties properties) {
		this.properties = properties;
	}

	@Override
	public Flux<RouteDefinition> getRouteDefinitions() {
		return Flux.fromIterable(this.properties.getRoutes());
	}

}

public class InMemoryRouteDefinitionRepository implements RouteDefinitionRepository {

	private final Map<String, RouteDefinition> routes = synchronizedMap(new LinkedHashMap<String, RouteDefinition>());

	@Override
	public Mono<Void> save(Mono<RouteDefinition> route) {
		return route.flatMap(r -> {
			if (ObjectUtils.isEmpty(r.getId())) {
				return Mono.error(new IllegalArgumentException("id may not be empty"));
			}
			routes.put(r.getId(), r);
			return Mono.empty();
		});
	}

	@Override
	public Mono<Void> delete(Mono<String> routeId) {
		return routeId.flatMap(id -> {
			if (routes.containsKey(id)) {
				routes.remove(id);
				return Mono.empty();
			}
			return Mono.defer(() -> Mono.error(new NotFoundException("RouteDefinition not found: " + routeId)));
		});
	}

	@Override
	public Flux<RouteDefinition> getRouteDefinitions() {
		Map<String, RouteDefinition> routesSafeCopy = new LinkedHashMap<>(routes);
		return Flux.fromIterable(routesSafeCopy.values());
	}

}

@Override
public void onApplicationEvent(RefreshRoutesEvent event) {
    try {
        // 如果是scoped的情况
        if (this.cache.containsKey(CACHE_KEY) && event.isScoped()) {
            // 调用重载的fetch方法来获取满足元数据的路由信息
            final Mono<List<Route>> scopedRoutes = fetch(event.getMetadata()).collect(Collectors.toList())
                    .onErrorResume(s -> Mono.just(List.of()));

            scopedRoutes.subscribe(scopedRoutesList -> {
                // 这里为什么要合并非scoped路由？这样岂不是将满足与不满足的都获取到了吗？那这里的scoped还有什么意义？
                Flux.concat(Flux.fromIterable(scopedRoutesList), getNonScopedRoutes(event)).materialize()
                        .collect(Collectors.toList()).subscribe(signals -> {
                            // 发布刷新路由结果事件，表示路由已刷新
                            applicationEventPublisher.publishEvent(new RefreshRoutesResultEvent(this));
                            // 修改cache
                            cache.put(CACHE_KEY, signals);
                        }, this::handleRefreshError);
            }, this::handleRefreshError);
        }
        else {
            // 重新获取所有路由
            final Mono<List<Route>> allRoutes = fetch().collect(Collectors.toList());

            allRoutes.subscribe(list -> Flux.fromIterable(list).materialize().collect(Collectors.toList())
                    .subscribe(signals -> {
                        applicationEventPublisher.publishEvent(new RefreshRoutesResultEvent(this));
                        // 重新设置路由信息
                        cache.put(CACHE_KEY, signals);
                    }, this::handleRefreshError), this::handleRefreshError);
        }
    }
    catch (Throwable e) {
        handleRefreshError(e);
    }
}

private Flux<Route> getNonScopedRoutes(RefreshRoutesEvent scopedEvent) {
    return this.getRoutes() // 获取路由
            // 筛选元数据不满足的那些路由
            .filter(route -> !RouteLocator.matchMetadata(route.getMetadata(), scopedEvent.getMetadata()));
}

private Flux<Route> fetch(Map<String, Object> metadata) {
    return this.delegate.getRoutesByMetadata(metadata).sort(AnnotationAwareOrderComparator.INSTANCE);
}

/*
 * 用于构建RouteLocator，方便创建路由定位器。
 */
@Bean
public RouteLocatorBuilder routeLocatorBuilder(ConfigurableApplicationContext context) {
    return new RouteLocatorBuilder(context);
}