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SpringCloud Gateway DispatcherHandler

Polarisy丶 人气:0

前言

之前几节我们分析了请求是如何调用到HttpWebHandlerAdapter的,然后再调用到DispatcherHandler中,通过handle方法来处理具体的请求。

DispatcherHandler的注入在自动装配那一节已经说过了,忘记的同学可以重新会看一下。

DispatcherHandler类声明

public class DispatcherHandler implements WebHandler, PreFlightRequestHandler, ApplicationContextAware {

可以看到实现了ApplicationContextAware接口,并实现了setApplicationContext方法

	@Override
	public void setApplicationContext(ApplicationContext applicationContext) {
		initStrategies(applicationContext);
	}
	protected void initStrategies(ApplicationContext context) {
		Map<String, HandlerMapping> mappingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(
				context, HandlerMapping.class, true, false);
		ArrayList<HandlerMapping> mappings = new ArrayList<>(mappingBeans.values());
		AnnotationAwareOrderComparator.sort(mappings);
		this.handlerMappings = Collections.unmodifiableList(mappings);
		Map<String, HandlerAdapter> adapterBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(
				context, HandlerAdapter.class, true, false);
		this.handlerAdapters = new ArrayList<>(adapterBeans.values());
		AnnotationAwareOrderComparator.sort(this.handlerAdapters);
		Map<String, HandlerResultHandler> beans = BeanFactoryUtils.beansOfTypeIncludingAncestors(
				context, HandlerResultHandler.class, true, false);
		this.resultHandlers = new ArrayList<>(beans.values());
		AnnotationAwareOrderComparator.sort(this.resultHandlers);
	}

可以看到,这里初始化了核心的三部分内容,具体是handlerMappingshandlerAdaptersresultHandlers

通过名字我们可以猜想它们的具体作用,后面会详细解析

handle方法

接下来我们来看下最核心的handle方法是如何具体处理请求的

	@Override
	public Mono<Void> handle(ServerWebExchange exchange) {
		if (this.handlerMappings == null) {
			return createNotFoundError();
		}
		if (CorsUtils.isPreFlightRequest(exchange.getRequest())) {
			return handlePreFlight(exchange);
		}
         //循环遍历所有的handlerMappings通过getHandler找到具体的handler
		return Flux.fromIterable(this.handlerMappings)
				.concatMap(mapping -> mapping.getHandler(exchange))
                  //next方法表示如果循环遍历handlerMappings时有多个匹配的handler,通过next方法只取出第一个匹配的handler执行下面的调用方法
				.next()
				.switchIfEmpty(createNotFoundError())
                   //处理具体的handler
				.flatMap(handler -> invokeHandler(exchange, handler))
                   //处理结果
				.flatMap(result -> handleResult(exchange, result));
	}

首先看getHandler方法

   	AbstractHandlerMapping.java
    @Override
	public Mono<Object> getHandler(ServerWebExchange exchange) {
		return getHandlerInternal(exchange).map(handler -> {
			if (logger.isDebugEnabled()) {
				logger.debug(exchange.getLogPrefix() + "Mapped to " + handler);
			}
			ServerHttpRequest request = exchange.getRequest();
			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;
				}
			}
			return handler;
		});
	}

其中会调用getHandlerInternal方法,是一个抽象方法

protected abstract Mono<?> getHandlerInternal(ServerWebExchange exchange);

通过断点调试可以看到,其中handlerMappings一共有四个

getHandlerInternal方法具体实现

可以分别去每个实现方法中断点查看不难找到RoutePredicateHandlerMapping就是我们需要的,通过名字可以猜到就是用来处理路由转发的

找到它的getHandlerInternal实现方法

	@Override
	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());
        //lookupRoute方法将根据配置文件中指定的predicates断言器和请求路径做匹配,如果匹配成功就会返回FilteringWebHandler
		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);
                      //上面定义的,private final FilteringWebHandler webHandler;
					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) + "]");
					}
				})));
	}

lookupRoute关于路由相关的以后单独再讲,现在知道了返回的handler就是FilteringWebHandler

下面关注invokeHandler方法

	private Mono<HandlerResult> invokeHandler(ServerWebExchange exchange, Object handler) {
		if (ObjectUtils.nullSafeEquals(exchange.getResponse().getStatusCode(), HttpStatus.FORBIDDEN)) {
			return Mono.empty();  // CORS rejection
		}
         //遍历所有的handlerAdapters找到能够支持当前handler的handlerAdapter,并执行handle方法
		if (this.handlerAdapters != null) {
			for (HandlerAdapter handlerAdapter : this.handlerAdapters) {
				if (handlerAdapter.supports(handler)) {
					return handlerAdapter.handle(exchange, handler);
				}
			}
		}
		return Mono.error(new IllegalStateException("No HandlerAdapter: " + handler));
	}

可以看到supports方法具体有四个实现

	@Override
	public boolean supports(Object handler) {
		return handler instanceof HandlerFunction;
	}
	@Override
	public boolean supports(Object handler) {
		return handler instanceof HandlerMethod;
	}
	@Override
	public boolean supports(Object handler) {
		return WebHandler.class.isAssignableFrom(handler.getClass());
	}
	@Override
	public boolean supports(Object handler) {
		return WebSocketHandler.class.isAssignableFrom(handler.getClass());
	}

我们目前支持的就是WebHandler,也就是会执行SimpleHandlerAdapter中的handle方法

	@Override
	public Mono<HandlerResult> handle(ServerWebExchange exchange, Object handler) {
         //FilteringWebHandler
		WebHandler webHandler = (WebHandler) handler;
		Mono<Void> mono = webHandler.handle(exchange);
		return mono.then(Mono.empty());
	}

之后会执行FilteringWebHandler的handle方法

	@Override
	public Mono<Void> handle(ServerWebExchange exchange) {
         //找到该请求对应的路由
		Route route = exchange.getRequiredAttribute(GATEWAY_ROUTE_ATTR);
         //找到该路由对应的GatewayFilter
		List<GatewayFilter> gatewayFilters = route.getFilters();
		//得到全局的的GatewayFilter
		List<GatewayFilter> combined = new ArrayList<>(this.globalFilters);
		combined.addAll(gatewayFilters);
		// TODO: needed or cached?
         //对全局过滤器和配置文件指定的路由局部过滤器统一排序
		AnnotationAwareOrderComparator.sort(combined);

		if (logger.isDebugEnabled()) {
			logger.debug("Sorted gatewayFilterFactories: " + combined);
		}
		//生成Gateway过滤器链,然后对客户端请求进行处理
		return new DefaultGatewayFilterChain(combined).filter(exchange);
	}

首先先看一下FilteringWebHandler在哪被注入的,通过搜索发现在GatewayAutoConfiguration中注入的

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

通过调试可以看到注入所有的GlobalFilter,默认有10个,并初始化

	public FilteringWebHandler(List<GlobalFilter> globalFilters) {
        //初始化时加载所有全局过滤器,将他们适配为GatewayFilter类型,方便等会做合并
		this.globalFilters = loadFilters(globalFilters);
	}
    //适配器模式,通过嵌套把GlobalFilter封装成GatewayFilter类型
	private static List<GatewayFilter> loadFilters(List<GlobalFilter> filters) {
		return filters.stream().map(filter -> {
             //GatewayFilterAdapter持有GlobalFilter对象
			GatewayFilterAdapter gatewayFilter = new GatewayFilterAdapter(filter);
			if (filter instanceof Ordered) {
                  //将后续用来排序的order值传进来
				int order = ((Ordered) filter).getOrder();
                  //OrderedGatewayFilter同样持有GatewayFilter对象
				return new OrderedGatewayFilter(gatewayFilter, order);
			}
			return gatewayFilter;
		}).collect(Collectors.toList());
	}

至于这里为什么要返回两种不同的对象分别持有GatewayFilter,主要和后面的排序相关

对于实现了Ordered接口的filter会返回OrderedGatewayFilter对象

接着回到前面的handle方法中,其中有一步就是用来排序的

AnnotationAwareOrderComparator.sort(combined);

通过调试可以找到具体的实现在OrderComparator

	@Override
	public int compare(@Nullable Object o1, @Nullable Object o2) {
		return doCompare(o1, o2, null);
	}
	private int doCompare(@Nullable Object o1, @Nullable Object o2, @Nullable OrderSourceProvider sourceProvider) {
        //谁实现了PriorityOrdered接口就代表谁的优先级高
		boolean p1 = (o1 instanceof PriorityOrdered);
		boolean p2 = (o2 instanceof PriorityOrdered);
		if (p1 && !p2) {
			return -1;
		}
		else if (p2 && !p1) {
			return 1;
		}
		int i1 = getOrder(o1, sourceProvider);
		int i2 = getOrder(o2, sourceProvider);
		return Integer.compare(i1, i2);
	}

如果都实现了PriorityOrdered接口或者都没有实现,那么通过getOrder方法得到的值来排序

	private int getOrder(@Nullable Object obj, @Nullable OrderSourceProvider sourceProvider) {
		Integer order = null;
		if (obj != null && sourceProvider != null) {
			Object orderSource = sourceProvider.getOrderSource(obj);
			if (orderSource != null) {
				if (orderSource.getClass().isArray()) {
					for (Object source : ObjectUtils.toObjectArray(orderSource)) {
						order = findOrder(source);
						if (order != null) {
							break;
						}
					}
				}
				else {
					order = findOrder(orderSource);
				}
			}
		}
		return (order != null ? order : getOrder(obj));
	}

传入的sourceProvider为null,最终调用另外一个getOrder方法

	protected int getOrder(@Nullable Object obj) {
		if (obj != null) {
			Integer order = findOrder(obj);
			if (order != null) {
				return order;
			}
		}
		return Ordered.LOWEST_PRECEDENCE;
	}

进入findOrder方法

	@Nullable
	protected Integer findOrder(Object obj) {
		return (obj instanceof Ordered ? ((Ordered) obj).getOrder() : null);
	}

可以看到,如果实现了Ordered接口,则调用重写的getOrder方法,否则返回null,最后会返回

Ordered.LOWEST_PRECEDENCE,代表最低的优先级

int LOWEST_PRECEDENCE = Integer.MAX_VALUE;

后面通过Integer.compare方法来比较,值越大的优先级越低

最后总结一下

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