1. Spring WebFlux是什么？
Spring WebFlux是Spring Framework 5.0中引入的新的反应式Web框架。 与Spring MVC不同，它不需要Servlet API，完全异步和非阻塞， 并通过Reactor项目实现Reactive Streams规范。 并且可以在诸如Netty，Undertow和Servlet 3.1+容器的服务器上运行。
Reactor 也是 Spring 5 中反应式编程的基础，它一个新的反应式编程库。
2. Reactor是什么？
Reactor offers non-blocking and backpressure-ready network runtimes including local TCP/HTTP/UDP client & servers based on the robust Netty framework.
Reactor提供了一个非阻塞的，高并发的基于健壮的Netty框架的网络运行API，包括本地tcp/http/udp 客户端和服务端。
重要的两个概念
Flux 和 Mono 是 Reactor 中的两个基本概念。Flux 表示的是包含 0 到 N 个元素的异步序列。在该序列中可以包含三种不同类型的消息通知：正常的包含元素的消息、序列结束的消息和序列出错的消息。当消息通知产生时，订阅者中对应的方法 onNext(), onComplete()和 onError()会被调用。Mono 表示的是包含 0 或者 1 个元素的异步序列。该序列中同样可以包含与 Flux 相同的三种类型的消息通知。Flux 和 Mono 之间可以进行转换。对一个 Flux 序列进行计数操作，得到的结果是一个 Mono<Long>对象。把两个 Mono 序列合并在一起，得到的是一个 Flux 对象。
简单说Mono返回单个元素，Flux返回多个元素
3. spring webflux处理请求流程
核心控制器DispatcherHandler，等同于阻塞方式的DispatcherServlet
/**
* Central dispatcher for HTTP request handlers/controllers. Dispatches to
* registered handlers for processing a request, providing convenient mapping
* facilities.
*
* <p>{@code DispatcherHandler} discovers the delegate components it needs from
* Spring configuration. It detects the following in the application context:
* <ul>
* <li>{@link HandlerMapping} -- map requests to handler objects
* <li>{@link HandlerAdapter} -- for using any handler interface
* <li>{@link HandlerResultHandler} -- process handler return values
* </ul>
*
* <p>{@code DispatcherHandler} is also designed to be a Spring bean itself and
* implements {@link ApplicationContextAware} for access to the context it runs
* in. If {@code DispatcherHandler} is declared with the bean name "webHandler"
* it is discovered by {@link WebHttpHandlerBuilder#applicationContext} which
* creates a processing chain together with {@code WebFilter},
* {@code WebExceptionHandler} and others.
*
* <p>A {@code DispatcherHandler} bean declaration is included in
* {@link org.springframework.web.reactive.config.EnableWebFlux @EnableWebFlux}
* configuration.
*
* @author Rossen Stoyanchev
* @author Sebastien Deleuze
* @author Juergen Hoeller
* @since 5.0
* @see WebHttpHandlerBuilder#applicationContext(ApplicationContext)
*/
3.1 初始化
获取HandlerMapping，HandlerAdapter，HandlerResultHandler的所有实例
protected void initStrategies(ApplicationContext context) {
Map<String, HandlerMapping> mappingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(
context, HandlerMapping.class, true, false); //1
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); //2
this.handlerAdapters = new ArrayList<>(adapterBeans.values());
AnnotationAwareOrderComparator.sort(this.handlerAdapters);
Map<String, HandlerResultHandler> beans = BeanFactoryUtils.beansOfTypeIncludingAncestors(
context, HandlerResultHandler.class, true, false); //3
this.resultHandlers = new ArrayList<>(beans.values());
AnnotationAwareOrderComparator.sort(this.resultHandlers);
}
其中，1.获取所有HandlerMapping实例
2.获取所有HandlerAdapter实例
3.获取所有HandlerResultHandler实例
3.2 流式处理请求
public Mono<Void> handle(ServerWebExchange exchange) {
if (this.handlerMappings == null) {
return createNotFoundError();
}
return Flux.fromIterable(this.handlerMappings)
.concatMap(mapping -> mapping.getHandler(exchange))//1
.next()
.switchIfEmpty(createNotFoundError())//2
.flatMap(handler -> invokeHandler(exchange, handler))//3
.flatMap(result -> handleResult(exchange, result));//4
}
其中，第一步，从handlerMapping这个map中获取HandlerMapping
第二步，触发HandlerApter的handle方法
private Mono<HandlerResult> invokeHandler(ServerWebExchange exchange, Object handler) {
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));
}
第三步，触发HandlerResultHandler 的handleResult方法
private Mono<Void> handleResult(ServerWebExchange exchange, HandlerResult result) {
return getResultHandler(result).handleResult(exchange, result)
.onErrorResume(ex -> result.applyExceptionHandler(ex).flatMap(exceptionResult ->
getResultHandler(exceptionResult).handleResult(exchange, exceptionResult)));
}
private HandlerResultHandler getResultHandler(HandlerResult handlerResult) {
if (this.resultHandlers != null) {
for (HandlerResultHandler resultHandler : this.resultHandlers) {
if (resultHandler.supports(handlerResult)) {
return resultHandler;
}
}
}
throw new IllegalStateException("No HandlerResultHandler for " + handlerResult.getReturnValue());
}
4.HandlerMapping实现
5.HanlderAdapter的实现
6.HandlerResultHandler的实现
7.不同容器的实现
7.1 Reactor实现ReactorHttpHandlerAdapter
执行apply方法
@Override
public Mono<Void> apply(HttpServerRequest reactorRequest, HttpServerResponse reactorResponse) {
NettyDataBufferFactory bufferFactory = new NettyDataBufferFactory(reactorResponse.alloc());
try {
ReactorServerHttpRequest request = new ReactorServerHttpRequest(reactorRequest, bufferFactory);
ServerHttpResponse response = new ReactorServerHttpResponse(reactorResponse, bufferFactory); if (request.getMethod() == HttpMethod.HEAD) {
response = new HttpHeadResponseDecorator(response);
} return this.httpHandler.handle(request, response)
.doOnError(ex -> logger.trace(request.getLogPrefix() + "Failed to complete: " + ex.getMessage()))
.doOnSuccess(aVoid -> logger.trace(request.getLogPrefix() + "Handling completed"));
}
catch (URISyntaxException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Failed to get request URI: " + ex.getMessage());
}
reactorResponse.status(HttpResponseStatus.BAD_REQUEST);
return Mono.empty();
}
}
其中，HttpHandler的定义
**
* Lowest level contract for reactive HTTP request handling that serves as a
* common denominator across different runtimes.
*
* <p>Higher-level, but still generic, building blocks for applications such as
* {@code WebFilter}, {@code WebSession}, {@code ServerWebExchange}, and others
* are available in the {@code org.springframework.web.server} package.
*
* <p>Application level programming models such as annotated controllers and
* functional handlers are available in the {@code spring-webflux} module.
*
* <p>Typically an {@link HttpHandler} represents an entire application with
* higher-level programming models bridged via
* {@link org.springframework.web.server.adapter.WebHttpHandlerBuilder}.
* Multiple applications at unique context paths can be plugged in with the
* help of the {@link ContextPathCompositeHandler}.
*
* @author Arjen Poutsma
* @author Rossen Stoyanchev
* @since 5.0
* @see ContextPathCompositeHandler
*/
具体的实现类为：ContextPathCompositeHandler
/**
* {@code HttpHandler} delegating requests to one of several {@code HttpHandler}'s
* based on simple, prefix-based mappings.
*
* <p>This is intended as a coarse-grained mechanism for delegating requests to
* one of several applications -- each represented by an {@code HttpHandler}, with
* the application "context path" (the prefix-based mapping) exposed via
* {@link ServerHttpRequest#getPath()}.
*
* @author Rossen Stoyanchev
* @since 5.0
*/
@Override
public Mono<Void> handle(ServerHttpRequest request, ServerHttpResponse response) {
// Remove underlying context path first (e.g. Servlet container)
String path = request.getPath().pathWithinApplication().value();
return this.handlerMap.entrySet().stream()
.filter(entry -> path.startsWith(entry.getKey()))
.findFirst()
.map(entry -> {
String contextPath = request.getPath().contextPath().value() + entry.getKey();
ServerHttpRequest newRequest = request.mutate().contextPath(contextPath).build();
return entry.getValue().handle(newRequest, response);
})
.orElseGet(() -> {
response.setStatusCode(HttpStatus.NOT_FOUND);
return response.setComplete();
});
}
基于前缀的映射Handler
7.2 Jetty实现JettyHttpHandlerAdapter
继承自ServletHttpHandlerAdapter 实现了Servlet，执行service方法
@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);//1
}
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);//2
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);//3
}
其中，1.创建request
2.创建response
3.handler执行的结果进行subscribe
JettyHttpHandlerAdapter是ServletHttpHandlerAdapter 的扩展，重写了创建request 创建response方法
7.3 Tomcat实现TomcatHttpHandlerAdapter
TomcatHttpHandlerAdapter是ServletHttpHandlerAdapter 的扩展，重写了创建request 创建response方法
7.4 AbstractReactiveWebInitializer抽象类
继承自AbstractReactiveWebInitializer的类可以在servlet容器中安装一个Spring Reactive Web Application。
@Override
public void onStartup(ServletContext servletContext) throws ServletException {
String servletName = getServletName();
Assert.hasLength(servletName, "getServletName() must not return null or empty"); ApplicationContext applicationContext = createApplicationContext();
Assert.notNull(applicationContext, "createApplicationContext() must not return null"); refreshApplicationContext(applicationContext);
registerCloseListener(servletContext, applicationContext); HttpHandler httpHandler = WebHttpHandlerBuilder.applicationContext(applicationContext).build();
ServletHttpHandlerAdapter servlet = new ServletHttpHandlerAdapter(httpHandler); ServletRegistration.Dynamic registration = servletContext.addServlet(servletName, servlet);
if (registration == null) {
throw new IllegalStateException("Failed to register servlet with name '" + servletName + "'. " +
"Check if there is another servlet registered under the same name.");
} registration.setLoadOnStartup(1);
registration.addMapping(getServletMapping());
registration.setAsyncSupported(true);
}
它通过将ServletHttpHandlerAdapter实例作为一个servlet安装到servler容器中。
8.总结
DispatcherHandler的流程是
1.通过 HandlerMapping（和DispathcherServlet中的HandlerMapping不同）获取到HandlerAdapter放到ServerWebExchange的属性中
2.获取到HandlerAdapter后触发handle方法，得到HandlerResult
3.通过HandlerResult，触发handleResult，针对不同的返回类找到不同的HandlerResultHandler如
视图渲染ViewResolutionResultHandler，
ServerResponseResultHandler,
ResponseBodyResultHandler,
ResponseEntityResultHandler
不同容器有不同的实现，如Reactor，Jetty，Tomcat等。
参考文献：
【1】https://blog.csdn.net/qq_15144655/article/details/80708915
【2】https://www.ibm.com/developerworks/cn/java/j-cn-with-reactor-response-encode/index.html