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本文主要研究一下spring cloud gateway的GlobalFilter

GatewayAutoConfiguration

spring-cloud-gateway-core-2.0.0.RC2-sources.jar!/org/springframework/cloud/gateway/config/GatewayAutoConfiguration.java

@Configuration
@ConditionalOnProperty(name = "spring.cloud.gateway.enabled", matchIfMissing = true)
@EnableConfigurationProperties
@AutoConfigureBefore(HttpHandlerAutoConfiguration.class)
@AutoConfigureAfter({GatewayLoadBalancerClientAutoConfiguration.class, GatewayClassPathWarningAutoConfiguration.class})
@ConditionalOnClass(DispatcherHandler.class)
public class GatewayAutoConfiguration {//......@Beanpublic FilteringWebHandler filteringWebHandler(List<GlobalFilter> globalFilters) {return new FilteringWebHandler(globalFilters);}@Beanpublic RoutePredicateHandlerMapping routePredicateHandlerMapping(FilteringWebHandler webHandler,RouteLocator routeLocator) {return new RoutePredicateHandlerMapping(webHandler, routeLocator);}//......
}
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• 这里将globalFilters(NettyWriteResponseFilter、ForwardPathFilter、RouteToRequestUrlFilter、LoadBalancerClientFilter、AdaptCachedBodyGlobalFilter、WebsocketRoutingFilter、NettyRoutingFilter、ForwardRoutingFilter)作为构造器参数创建了FilteringWebHandler
• 而依据FilteringWebHandler和RouteLocator创建了RoutePredicateHandlerMapping，这里的RouteLocator是CachingRouteLocator

FilteringWebHandler

spring-cloud-gateway-core-2.0.0.RC2-sources.jar!/org/springframework/cloud/gateway/handler/FilteringWebHandler.java

/*** WebHandler that delegates to a chain of {@link GlobalFilter} instances and* {@link GatewayFilterFactory} instances then to the target {@link WebHandler}.** @author Rossen Stoyanchev* @author Spencer Gibb* @since 0.1*/
public class FilteringWebHandler implements WebHandler {protected static final Log logger = LogFactory.getLog(FilteringWebHandler.class);private final List<GatewayFilter> globalFilters;public FilteringWebHandler(List<GlobalFilter> globalFilters) {this.globalFilters = loadFilters(globalFilters);}private static List<GatewayFilter> loadFilters(List<GlobalFilter> filters) {return filters.stream().map(filter -> {GatewayFilterAdapter gatewayFilter = new GatewayFilterAdapter(filter);if (filter instanceof Ordered) {int order = ((Ordered) filter).getOrder();return new OrderedGatewayFilter(gatewayFilter, order);}return gatewayFilter;}).collect(Collectors.toList());}/* TODO: relocate @EventListener(RefreshRoutesEvent.class)void handleRefresh() {this.combinedFiltersForRoute.clear();}*/@Overridepublic Mono<Void> handle(ServerWebExchange exchange) {Route route = exchange.getRequiredAttribute(GATEWAY_ROUTE_ATTR);List<GatewayFilter> gatewayFilters = route.getFilters();List<GatewayFilter> combined = new ArrayList<>(this.globalFilters);combined.addAll(gatewayFilters);//TODO: needed or cached?AnnotationAwareOrderComparator.sort(combined);logger.debug("Sorted gatewayFilterFactories: "+ combined);return new DefaultGatewayFilterChain(combined).filter(exchange);}//......
}
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• 这里在构造器里头调用loadFilters方法把List转换为List
• 之后的handle方法，把选定的route的gatewayFilters与转换后的gatewayFilters合并，然后重新排序
• 之后使用合并后的gatewayFilters创建DefaultGatewayFilterChain，挨个filter下去

GatewayFilterAdapter

  private static class GatewayFilterAdapter implements GatewayFilter {private final GlobalFilter delegate;public GatewayFilterAdapter(GlobalFilter delegate) {this.delegate = delegate;}@Overridepublic Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {return this.delegate.filter(exchange, chain);}@Overridepublic String toString() {final StringBuilder sb = new StringBuilder("GatewayFilterAdapter{");sb.append("delegate=").append(delegate);sb.append('}');return sb.toString();}}
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这里将GlobalFilter适配为GatewayFilter，最后调用filter方法

DefaultGatewayFilterChain

   private static class DefaultGatewayFilterChain implements GatewayFilterChain {private final int index;private final List<GatewayFilter> filters;public DefaultGatewayFilterChain(List<GatewayFilter> filters) {this.filters = filters;this.index = 0;}private DefaultGatewayFilterChain(DefaultGatewayFilterChain parent, int index) {this.filters = parent.getFilters();this.index = index;}public List<GatewayFilter> getFilters() {return filters;}@Overridepublic Mono<Void> filter(ServerWebExchange exchange) {return Mono.defer(() -> {if (this.index < filters.size()) {GatewayFilter filter = filters.get(this.index);DefaultGatewayFilterChain chain = new DefaultGatewayFilterChain(this, this.index + 1);return filter.filter(exchange, chain);} else {return Mono.empty(); // complete}});}}
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这里使用了责任链模式，里头filter方法，挨个遍历执行，传入的chain包含了当前的index，用于控制跳出责任链

RoutePredicateHandlerMapping

spring-cloud-gateway-core-2.0.0.RC2-sources.jar!/org/springframework/cloud/gateway/handler/RoutePredicateHandlerMapping.java

public class RoutePredicateHandlerMapping extends AbstractHandlerMapping {private final FilteringWebHandler webHandler;private final RouteLocator routeLocator;public RoutePredicateHandlerMapping(FilteringWebHandler webHandler, RouteLocator routeLocator) {this.webHandler = webHandler;this.routeLocator = routeLocator;setOrder(1);}@Overrideprotected Mono<?> getHandlerInternal(ServerWebExchange exchange) {exchange.getAttributes().put(GATEWAY_HANDLER_MAPPER_ATTR, getClass().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) + "]");}})));}@Overrideprotected CorsConfiguration getCorsConfiguration(Object handler, ServerWebExchange exchange) {//TODO: support cors configuration via global properties and// properties on a route see gh-229// see RequestMappingHandlerMapping.initCorsConfiguration()// also see https://github.com/spring-projects/spring-framework/blob/master/spring-web/src/test/java/org/springframework/web/cors/reactive/CorsWebFilterTests.javareturn super.getCorsConfiguration(handler, exchange);}//......
}
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这个RoutePredicateHandlerMapping主要是实现了父类的getHandlerInternal

DispatcherHandler

spring-webflux-5.0.6.RELEASE-sources.jar!/org/springframework/web/reactive/DispatcherHandler.java

/*** Central dispatcher for HTTP request handlers/controllers. Dispatches to* registered handlers for processing a request, providing convenient mapping* facilities.** <p>{@code DispatcherHandler} discovers the delegate components it needs from* Spring configuration. It detects the following in the application context:* <ul>* <li>{@link HandlerMapping} -- map requests to handler objects* <li>{@link HandlerAdapter} -- for using any handler interface* <li>{@link HandlerResultHandler} -- process handler return values* </ul>** <p>{@code DispatcherHandler} is also designed to be a Spring bean itself and* implements {@link ApplicationContextAware} for access to the context it runs* in. If {@code DispatcherHandler} is declared with the bean name "webHandler"* it is discovered by {@link WebHttpHandlerBuilder#applicationContext} which* creates a processing chain together with {@code WebFilter},* {@code WebExceptionHandler} and others.** <p>A {@code DispatcherHandler} bean declaration is included in* {@link org.springframework.web.reactive.config.EnableWebFlux @EnableWebFlux}* configuration.** @author Rossen Stoyanchev* @author Sebastien Deleuze* @author Juergen Hoeller* @since 5.0* @see WebHttpHandlerBuilder#applicationContext(ApplicationContext)*/
public class DispatcherHandler implements WebHandler, ApplicationContextAware {@SuppressWarnings("ThrowableInstanceNeverThrown")private static final Exception HANDLER_NOT_FOUND_EXCEPTION =new ResponseStatusException(HttpStatus.NOT_FOUND, "No matching handler");private static final Log logger = LogFactory.getLog(DispatcherHandler.class);@Nullableprivate List<HandlerMapping> handlerMappings;@Nullableprivate List<HandlerAdapter> handlerAdapters;@Nullableprivate List<HandlerResultHandler> resultHandlers;//......@Overridepublic 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);}@Overridepublic Mono<Void> handle(ServerWebExchange exchange) {if (logger.isDebugEnabled()) {ServerHttpRequest request = exchange.getRequest();logger.debug("Processing " + request.getMethodValue() + " request for [" + request.getURI() + "]");}if (this.handlerMappings == null) {return Mono.error(HANDLER_NOT_FOUND_EXCEPTION);}return Flux.fromIterable(this.handlerMappings).concatMap(mapping -> mapping.getHandler(exchange)).next().switchIfEmpty(Mono.error(HANDLER_NOT_FOUND_EXCEPTION)).flatMap(handler -> invokeHandler(exchange, handler)).flatMap(result -> handleResult(exchange, result));}//......
}
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• 这里setApplicationContext的时候调用了initStrategies方法
• 使用BeanFactoryUtils.beansOfTypeIncludingAncestors获取了容器中注册的HandlerMapping
• RoutePredicateHandlerMapping注册到了容器中，这里会被获取到
• handlerMapping用于根据exchange来获取handler
• 这了使用的是concatMap，如果返回的是Mono.empty()则不会被concat，然后next取第一个，即按handlerMappings排序之后的第一个来

handlerMappings

这里按优先级从高到底有如下几个：

• WebFluxEndpointHandlerMapping(order=-100)
• ControllerEndpointHandlerMapping(order=-100)
• RouterFunctionMapping(order=-1)
• RequestMappingHandlerMapping(order=0)
• RoutePredicateHandlerMapping(order=1)
• SimpleUrlHandlerMapping(Ordered.LOWEST_PRECEDENCE)

小结

spring cloud gateway的GlobalFilter在FilteringWebHandler被适配为GatewayFilter，然后与route级别的gatewayFilters进行合并，作用在当前route上面。RoutePredicateHandlerMapping会被DispatcherHandler识别，按order优先级排序，依次根据mapping来获取该exchange的handler，找到不是Mono.empty()的第一个，然后进行invokeHandler以及handleResult。

因此可以理解为GlobalFilter就是全局的GatewayFilter，作用在所有route上面。而GatewayFilter是route级别的。

doc

• 113. Global Filters
• 聊聊spring cloud gateway的RouteLocator