上一节做了一个很简单的示例,微服务通过注册到eureka上,然后网关通过服务发现访问到对应的微服务。本节将简单地对整个gateway请求转发过程做一个简单的分析。
一、核心流程
主要流程:
- Gateway Client向 Spring Cloud Gateway 发送请求
- 请求首先会被HttpWebHandlerAdapter 进行提取组装成网关上下文
- 然后网关的上下文会传递到DispatcherHandler ,它负责将请求分发给 RoutePredicateHandlerMapping
- RoutePredicateHandlerMapping负责路由查找,并根据路由断言判断路由是否可用
- 如果过断言成功,由FilteringWebHandler 创建过滤器链并调用
- 通过特定于请求的 Fliter 链运行请求,Filter 被虚线分隔的原因是Filter可以在发送代理请求之前(pre)和之后(post)运行逻辑
- 执行所有pre过滤器逻辑。然后进行代理请求。发出代理请求后,将运行“post”过滤器逻辑。
- 处理完毕之后将 Response 返回到 Gateway 客户端
二、具体分析
请求过来,会经过HttpWebHandlerAdapter.handle方法,可以理解为这就是请求的主入口
@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();
}
}
//组装上下文
ServerWebExchange exchange = createExchange(request, response);
LogFormatUtils.traceDebug(logger, traceOn ->
exchange.getLogPrefix() + formatRequest(exchange.getRequest()) +
(traceOn ? ", headers=" + formatHeaders(exchange.getRequest().getHeaders()) : ""));
//委派给delegate来处理
return getDelegate().handle(exchange)
.doOnSuccess(aVoid -> logResponse(exchange))
.onErrorResume(ex -> handleUnresolvedError(exchange, ex))
.then(Mono.defer(response::setComplete));
}
这一个delegate是个啥,看一下接口定义:
就是一个处理器,所有参数封装在上下文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);
}
最终会调到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
是一个列表,HandlerMapping可以根据当前请求,找到对应的处理器
如果当前请求比如/hello/world,在gateway服务上是一个controller对应的接口,那这个就可以通过RequestMappingHandlerMapping找到一个RequestMappingHandlerAdapter。
如果当前请求,是需要转发给下游微服务的,则找到RoutePredicateHandlerMapping
RoutePredicateHandlerMapping查找路由主要逻辑
@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实际上是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) + "]");
}
})));
}
看下查找路由的具体方式:原来是将所有的路由,用predicate作一下匹配,找出符合当前请求的路由
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,找出符合当前请求的路由
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,用了服务注册和发现后,实际上,一个微服务会自动注册一个路由,比如上面的hello-service,自动注册了一个路径为:/hello-service/**的路由。这就是为什么我们yml配置文件中明明什么路由也没有配置,也能自动转发hello-service的请求。
同时,可以看到,这个路由下面有一个ReWritePathFilter,会自动去掉服务名,将请求转发给下游微服务。
下一步再看看FilteringWebHandler中的处理逻辑
@Override
public Mono<Void> handle(ServerWebExchange exchange) {
//从上下文中取出路由,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也取出来
List<GatewayFilter> combined = new ArrayList<>(this.globalFilters);
combined.addAll(gatewayFilters);
// TODO: needed or cached?
//做个排序
AnnotationAwareOrderComparator.sort(combined);
if (logger.isDebugEnabled()) {
logger.debug("Sorted gatewayFilterFactories: " + combined);
}
//后面就是filter链式调用了
return new DefaultGatewayFilterChain(combined).filter(exchange);
}
可以看到代码中主要有两个逻辑:
1、从上下文中取出路由,路由中包含filters
2、spring容器中的Global Filter也取出来
3、合并上面的两种filter,并且排序
4、filters列表组装成责任链来进行调用
可以通过源码,再来看看核心流程的那个图,这样就比较清楚了。
总结了另一个稍微详细一点的图:
文章来源:https://www.toymoban.com/news/detail-695942.html
个人看这块源码的体会:整个核心流程并不复杂,难点大概是reactor响应式编程,如果之前没接触过这一块,那么看着会有种不知道下一步往哪里的困惑!所以要学习这块源码,还得学习reactor。文章来源地址https://www.toymoban.com/news/detail-695942.html
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