Soul网关(18) - WebHandler接口

话不多说，上来就干

在阅读soul源码的过程中，我发现了一个请求处理接口 WebHandler，之所以发现这个接口，是因为网关中，对于请求的处理，都是通过 SoulWebHandler接口的具体方法处理的，而这个接口就是直接继承了spring的 WebHandler接口

/**
 * Contract to handle a web request.
 *
 * <p>Use {@link HttpWebHandlerAdapter} to adapt a {@code WebHandler} to an
 * {@link org.springframework.http.server.reactive.HttpHandler HttpHandler}.
 * The {@link WebHttpHandlerBuilder} provides a convenient way to do that while
 * also optionally configuring one or more filters and/or exception handlers.
 *
 * @author Rossen Stoyanchev
 * @since 5.0
 */
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);

}

这接口是spring5新增的接口，用于使用reative编程处理web强求，webhandler接口的唯一方法会被一个http请求的适配器 HttpWebHandlerAdapter处理

	@Override
	public Mono<Void> handle(ServerHttpRequest request, ServerHttpResponse response) {
		if (this.forwardedHeaderTransformer != null) {
			request = this.forwardedHeaderTransformer.apply(request);
		}
		ServerWebExchange exchange = createExchange(request, response);

		LogFormatUtils.traceDebug(logger, traceOn ->
				exchange.getLogPrefix() + formatRequest(exchange.getRequest()) +
						(traceOn ? ", headers=" + formatHeaders(exchange.getRequest().getHeaders()) : ""));

       // webhandler 被调用
		return getDelegate().handle(exchange)
				.doOnSuccess(aVoid -> logResponse(exchange))
				.onErrorResume(ex -> handleUnresolvedError(exchange, ex))
				.then(Mono.defer(response::setComplete));
	}

	protected ServerWebExchange createExchange(ServerHttpRequest request, ServerHttpResponse response) {
		return new DefaultServerWebExchange(request, response, this.sessionManager,
				getCodecConfigurer(), getLocaleContextResolver(), this.applicationContext);
	}

适配器最终会被 ServletHttpHandlerAdapter的service方法调用，而这个service方式很熟悉，就是我们最初学习java的serlvet容器中必须要实现那个service，用来处理http请求，这个适配器最终就是java的 Servlet接口的具体实现

	@Override
	public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException {
		// Check for existing error attribute first
		if (DispatcherType.ASYNC.equals(request.getDispatcherType())) {
			Throwable ex = (Throwable) request.getAttribute(WRITE_ERROR_ATTRIBUTE_NAME);
			throw new ServletException("Failed to create response content", ex);
		}

		// Start async before Read/WriteListener registration
		AsyncContext asyncContext = request.startAsync();
		asyncContext.setTimeout(-1);

		ServletServerHttpRequest httpRequest;
		try {
			httpRequest = createRequest(((HttpServletRequest) request), asyncContext);
		}
		catch (URISyntaxException ex) {
			if (logger.isDebugEnabled()) {
				logger.debug("Failed to get request  URL: " + ex.getMessage());
			}
			((HttpServletResponse) response).setStatus(400);
			asyncContext.complete();
			return;
		}

		ServerHttpResponse httpResponse = createResponse(((HttpServletResponse) response), asyncContext, httpRequest);
		if (httpRequest.getMethod() == HttpMethod.HEAD) {
			httpResponse = new HttpHeadResponseDecorator(httpResponse);
		}

		AtomicBoolean isCompleted = new AtomicBoolean();
		HandlerResultAsyncListener listener = new HandlerResultAsyncListener(isCompleted, httpRequest);
		asyncContext.addListener(listener);

		HandlerResultSubscriber subscriber = new HandlerResultSubscriber(asyncContext, isCompleted, httpRequest);
		this.httpHandler.handle(httpRequest, httpResponse).subscribe(subscriber);
	}

继承了这个service方法的接口就有大名鼎鼎的 GenericServlet 通用servlet接口，他也是springmvc的核心调度器 DispatcherServlet的间接父类

可见spring新增的响应式编程在同一的servlet框架下，很好的兼容了之前的springmvc框架