上一節(jié)做了一個(gè)很簡單的示例，微服務(wù)通過注冊到eureka上，然后網(wǎng)關(guān)通過服務(wù)發(fā)現(xiàn)訪問到對(duì)應(yīng)的微服務(wù)。本節(jié)將簡單地對(duì)整個(gè)gateway請(qǐng)求轉(zhuǎn)發(fā)過程做一個(gè)簡單的分析。
一、核心流程
主要流程：
- Gateway Client向 Spring Cloud Gateway 發(fā)送請(qǐng)求
- 請(qǐng)求首先會(huì)被HttpWebHandlerAdapter 進(jìn)行提取組裝成網(wǎng)關(guān)上下文
- 然后網(wǎng)關(guān)的上下文會(huì)傳遞到DispatcherHandler ，它負(fù)責(zé)將請(qǐng)求分發(fā)給 RoutePredicateHandlerMapping
- RoutePredicateHandlerMapping負(fù)責(zé)路由查找，并根據(jù)路由斷言判斷路由是否可用
- 如果過斷言成功，由FilteringWebHandler 創(chuàng)建過濾器鏈并調(diào)用
- 通過特定于請(qǐng)求的 Fliter 鏈運(yùn)行請(qǐng)求，F(xiàn)ilter 被虛線分隔的原因是Filter可以在發(fā)送代理請(qǐng)求之前（pre）和之后（post）運(yùn)行邏輯
- 執(zhí)行所有pre過濾器邏輯。然后進(jìn)行代理請(qǐng)求。發(fā)出代理請(qǐng)求后，將運(yùn)行“post”過濾器邏輯。
- 處理完畢之后將 Response 返回到 Gateway 客戶端
二、具體分析
請(qǐng)求過來，會(huì)經(jīng)過HttpWebHandlerAdapter.handle方法，可以理解為這就是請(qǐng)求的主入口
@Override
public Mono<Void> handle(ServerHttpRequest request, ServerHttpResponse response) {
if (this.forwardedHeaderTransformer != null) {
try {
request = this.forwardedHeaderTransformer.apply(request);
}
catch (Throwable ex) {
if (logger.isDebugEnabled()) {
logger.debug("Failed to apply forwarded headers to " + formatRequest(request), ex);
}
response.setStatusCode(HttpStatus.BAD_REQUEST);
return response.setComplete();
}
}
//組裝上下文
ServerWebExchange exchange = createExchange(request, response);
LogFormatUtils.traceDebug(logger, traceOn ->
exchange.getLogPrefix() + formatRequest(exchange.getRequest()) +
(traceOn ? ", headers=" + formatHeaders(exchange.getRequest().getHeaders()) : ""));
//委派給delegate來處理
return getDelegate().handle(exchange)
.doOnSuccess(aVoid -> logResponse(exchange))
.onErrorResume(ex -> handleUnresolvedError(exchange, ex))
.then(Mono.defer(response::setComplete));
}
這一個(gè)delegate是個(gè)啥，看一下接口定義：
就是一個(gè)處理器，所有參數(shù)封裝在上下文exchange中
public interface WebHandler {
/**
* Handle the web server exchange.
* @param exchange the current server exchange
* @return {@code Mono<Void>} to indicate when request handling is complete
*/
Mono<Void> handle(ServerWebExchange exchange);
}
最終會(huì)調(diào)到DispatcherHandler
@Override
public Mono<Void> handle(ServerWebExchange exchange) {
if (this.handlerMappings == null) {
return createNotFoundError();
}
if (CorsUtils.isPreFlightRequest(exchange.getRequest())) {
return handlePreFlight(exchange);
}
return Flux.fromIterable(this.handlerMappings)
.concatMap(mapping -> mapping.getHandler(exchange))
.next()
.switchIfEmpty(createNotFoundError())
.flatMap(handler -> invokeHandler(exchange, handler))
.flatMap(result -> handleResult(exchange, result));
}
handlerMappings是啥
是一個(gè)列表，HandlerMapping可以根據(jù)當(dāng)前請(qǐng)求，找到對(duì)應(yīng)的處理器
如果當(dāng)前請(qǐng)求比如/hello/world，在gateway服務(wù)上是一個(gè)controller對(duì)應(yīng)的接口，那這個(gè)就可以通過RequestMappingHandlerMapping找到一個(gè)RequestMappingHandlerAdapter。
如果當(dāng)前請(qǐng)求，是需要轉(zhuǎn)發(fā)給下游微服務(wù)的，則找到RoutePredicateHandlerMapping
RoutePredicateHandlerMapping查找路由主要邏輯
@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().getLocalAddress() != null
&& exchange.getRequest().getLocalAddress().getPort() == this.managementPort) {
return Mono.empty();
}
exchange.getAttributes().put(GATEWAY_HANDLER_MAPPER_ATTR, 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);
}
//把找到的路由放到exchange上下文中
exchange.getAttributes().put(GATEWAY_ROUTE_ATTR, r);
//返回的handler實(shí)際上是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) + "]");
}
})));
}
看下查找路由的具體方式：原來是將所有的路由，用predicate作一下匹配，找出符合當(dāng)前請(qǐng)求的路由
protected Mono<Route> lookupRoute(ServerWebExchange exchange) {
return this.routeLocator.getRoutes()
// individually filter routes so that filterWhen error delaying is not a
// problem
.concatMap(route -> Mono.just(route).filterWhen(r -> {
// add the current route we are testing
exchange.getAttributes().put(GATEWAY_PREDICATE_ROUTE_ATTR, r.getId());
//用predicate作一下匹配，找出符合當(dāng)前請(qǐng)求的路由
return r.getPredicate().apply(exchange);
})
// instead of immediately stopping main flux due to error, log and
// swallow it
.doOnError(e -> logger.error("Error applying predicate for route: " + route.getId(), e))
.onErrorResume(e -> Mono.empty()))
// .defaultIfEmpty() put a static Route not found
// or .switchIfEmpty()
// .switchIfEmpty(Mono.<Route>empty().log("noroute"))
.next()
// TODO: error handling
.map(route -> {
if (logger.isDebugEnabled()) {
logger.debug("Route matched: " + route.getId());
}
validateRoute(route, exchange);
return route;
});
/*
* TODO: trace logging if (logger.isTraceEnabled()) {
* logger.trace("RouteDefinition did not match: " + routeDefinition.getId()); }
*/
}
routeLocator包含了哪些路由，Debug看一下
可以看到，用了服務(wù)注冊和發(fā)現(xiàn)后，實(shí)際上，一個(gè)微服務(wù)會(huì)自動(dòng)注冊一個(gè)路由，比如上面的hello-service，自動(dòng)注冊了一個(gè)路徑為：/hello-service/**的路由。這就是為什么我們yml配置文件中明明什么路由也沒有配置，也能自動(dòng)轉(zhuǎn)發(fā)hello-service的請(qǐng)求。
同時(shí)，可以看到，這個(gè)路由下面有一個(gè)ReWritePathFilter，會(huì)自動(dòng)去掉服務(wù)名，將請(qǐng)求轉(zhuǎn)發(fā)給下游微服務(wù)。
下一步再看看FilteringWebHandler中的處理邏輯
@Override
public Mono<Void> handle(ServerWebExchange exchange) {
//從上下文中取出路由，路由中包含filters
Route route = exchange.getRequiredAttribute(GATEWAY_ROUTE_ATTR);
List<GatewayFilter> gatewayFilters = route.getFilters();
//spring容器中的Global Filter也取出來
List<GatewayFilter> combined = new ArrayList<>(this.globalFilters);
combined.addAll(gatewayFilters);
// TODO: needed or cached?
//做個(gè)排序
AnnotationAwareOrderComparator.sort(combined);
if (logger.isDebugEnabled()) {
logger.debug("Sorted gatewayFilterFactories: " + combined);
}
//后面就是filter鏈?zhǔn)秸{(diào)用了
return new DefaultGatewayFilterChain(combined).filter(exchange);
}
可以看到代碼中主要有兩個(gè)邏輯：
1、從上下文中取出路由，路由中包含filters
2、spring容器中的Global Filter也取出來
3、合并上面的兩種filter,并且排序
4、filters列表組裝成責(zé)任鏈來進(jìn)行調(diào)用
可以通過源碼，再來看看核心流程的那個(gè)圖，這樣就比較清楚了。
總結(jié)了另一個(gè)稍微詳細(xì)一點(diǎn)的圖：
文章來源：http://www.zghlxwxcb.cn/news/detail-695942.html
個(gè)人看這塊源碼的體會(huì)：整個(gè)核心流程并不復(fù)雜，難點(diǎn)大概是reactor響應(yīng)式編程，如果之前沒接觸過這一塊，那么看著會(huì)有種不知道下一步往哪里的困惑！所以要學(xué)習(xí)這塊源碼，還得學(xué)習(xí)reactor。文章來源地址http://www.zghlxwxcb.cn/news/detail-695942.html
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