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。
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handlerMappings，handlerAdapters，resultHandlers
通过名字我们可以猜想它们的具体作用，后面会详细解析
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中
@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
PriorityOrdered接口就代表谁的优先级高Ordered接口Ordered接口，那么返回实现方法中getOrder的值Ordered接口，那么返回最低的优先级也就是Integer的最大值
