Spring Cloud Gateway系列(一):整体流程

GateWay作为Spring Cloud的全新项目用来取代旧版本中的Netflix Zuul，从而实现更高的性能，本系列将会以下三个部分：

整体流程全局CORS配置动态路由刷新

使用配置文件配置的样例：

Gateway接收到来自客户端的请求之后，请求首先进入HttpWebHandlerAdapter 类：

@Override
public Mono handle(ServerHttpRequest request, ServerHttpResponse response) {
	if (this.forwardedHeaderTransformer != null) {
		request = this.forwardedHeaderTransformer.apply(request);
	}
    //过滤器中使用的ServerWebExchange就是在这里创建的DefaultServerWebExchange
	ServerWebExchange exchange = createExchange(request, response);

	LogFormatUtils.traceDebug(logger, traceOn ->
			exchange.getLogPrefix() + formatRequest(exchange.getRequest()) +
						(traceOn ? ", headers=" + formatHeaders(exchange.getRequest().getHeaders()) : ""));
    //getDelegate()返回的是ExceptionHandlingWebHandler
	return getDelegate().handle(exchange)
			.doonSuccess(aVoid -> logResponse(exchange))
			.onErrorResume(ex -> handleUnresolvedError(exchange, ex))
			.then(Mono.defer(response::setComplete));
}

 ExceptionHandlingWebHandler类的handle(exchange)方法调用其父类WebHandlerDecorator的handle(exchange)方法，最终会调用FilteringWebHandler的hanlde(exchange)方法。

//ExceptionHandlingWebHandler类
@Override
public Mono handle(ServerWebExchange exchange) {

		Mono completion;
		try {
            //调用父类WebHandlerDecorator的handle方法
			completion = super.handle(exchange);
		}
		catch (Throwable ex) {
			completion = Mono.error(ex);
		}

		for (WebExceptionHandler handler : this.exceptionHandlers) {
			completion = completion.onErrorResume(ex -> handler.handle(exchange, ex));
		}

		return completion;
}

//WebHandlerDecorator类
@Override
public Mono handle(ServerWebExchange exchange) {
        //调用FilteringWebHandler.handle(exchange)方法
		return this.delegate.handle(exchange);
}

//FilteringWebHandler类
@Override
public Mono handle(ServerWebExchange exchange) {
		return this.chain.filter(exchange);
}

 然后进入DefaultWebFilterChain的filter(exchange)方法

@Override
public Mono filter(ServerWebExchange exchange) {
    
	return Mono.defer(() ->
	this.currentFilter != null && this.next != null ?
			this.currentFilter.filter(exchange, this.next) :
			this.handler.handle(exchange));
}

核心类DispatcherHandler:

@Override
public Mono handle(ServerWebExchange exchange) {
	if (this.handlerMappings == null) {
		return createNotFoundError();
	}
          
	return Flux.fromIterable(this.handlerMappings)
			.concatMap(mapping -> mapping.getHandler(exchange))
			.next()
			.switchIfEmpty(createNotFoundError())
			.flatMap(handler -> invokeHandler(exchange, handler))
			.flatMap(result -> handleResult(exchange, result));
}

 mapping.getHandler(exchange)方法会执行AbstractHandlerMapping的getHandler(exchange)方法，我们在配置文件中指定的全局跨域规则就是在这个方法里生效的！

@Override
public Mono