一文带你彻底理解SpringWebFlux的工作原理

1 、请求入口HttpHandler

自动配置

public class HttpHandlerAutoConfiguration {
    @Configuration(proxyBeanMethods = false)
    public static class AnnotationConfig {
        private final ApplicationContext applicationContext;
        public AnnotationConfig(ApplicationContext applicationContext) {
            this.applicationContext = applicationContext;
        }
        @Bean
        public HttpHandler httpHandler(ObjectProvider propsProvider) {
            HttpHandler httpHandler = WebHttpHandlerBuilder.applicationContext(this.applicationContext).build();
            WebFluxProperties properties = propsProvider.getIfAvailable();
            if (properties != null && StringUtils.hasText(properties.getBasePath())) {
                Map handlersMap = Collections.singletonMap(properties.getBasePath(), httpHandler);
                return new ContextPathCompositeHandler(handlersMap);
            }
            return httpHandler;
        }
    }
}

这个自动配置与DispatcherServletAutoConfiguration相对应;HttpHandler是WebFlux环境下的核心处理器类。

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其中这里的WebHttpHandlerBuilder.applicationContext(this.applicationContext).build()代码就是用来构建HttpWebHandlerAdapter对象。

核心处理类 HttpWebHandlerAdapter。

public class HttpWebHandlerAdapter extends WebHandlerDecorator implements HttpHandler {
    // 请求入口
    public Mono handle(ServerHttpRequest request, ServerHttpResponse response) {
        if (this.forwardedHeaderTransformer != null) {
            try {
                request = this.forwardedHeaderTransformer.apply(request);
            } catch (Throwable ex) {
                response.setStatusCode(HttpStatus.BAD_REQUEST);
                return response.setComplete();
            }
        }
        ServerWebExchange exchange = createExchange(request, response);
        // 获取委托类，最终是由委托的WebHandler进行处理
        // 1.1
        return getDelegate().handle(exchange)
                .doOnSuccess(aVoid -> logResponse(exchange))
                .onErrorResume(ex -> handleUnresolvedError(exchange, ex))
                .then(Mono.defer(response::setComplete));
    }
}

一个请求是如何通过上面的HttpWebHandlerAdapter执行调用处理的?

容器在启动执行refresh核心方法：

public abstract class AbstractApplicationContext {
    public void refresh() throws BeansException, IllegalStateException {
        // ...
        // 执行子类方法
        onRefresh();
        // ...
    }
}
public class ReactiveWebServerApplicationContext {
    protected void onRefresh() {
        // ...
        createWebServer();
        // ...
    }
    private void createWebServer() {
        WebServerManager serverManager = this.serverManager;
        if (serverManager == null) {
            // ...
            // this::getHttpHandler方法获取上面的HttpHandler对象
            this.serverManager = new WebServerManager(this, webServerFactory, this::getHttpHandler, lazyInit);
            // ...
        }
        initPropertySources();
    }
    protected HttpHandler getHttpHandler() {
        String[] beanNames = getBeanFactory().getBeanNamesForType(HttpHandler.class);
        // ...
        return getBeanFactory().getBean(beanNames[0], HttpHandler.class);
    }
}

（1） 请求处理委托类WebHandler

getDelegate方法返回的调用的是父类WebHandlerDecorator方法：

public class WebHandlerDecorator implements WebHandler {
    private final WebHandler delegate;
    public WebHandlerDecorator(WebHandler delegate) {\
        this.delegate = delegate;
    }
    public WebHandler getDelegate() {
        return this.delegate;
    }
}

这里的delegate是谁?

（2） HttpWebHandlerAdapter创建

自动配置

public class HttpHandlerAutoConfiguration {
    @Configuration(proxyBeanMethods = false)
    public static class AnnotationConfig {
        private final ApplicationContext applicationContext;
        public AnnotationConfig(ApplicationContext applicationContext) {
            this.applicationContext = applicationContext;
        }
        @Bean
        public HttpHandler httpHandler(ObjectProvider propsProvider) {
            // 这里通过WebHttpHandlerBuilder对象创建HttpWebHandlerAdapter对象
            HttpHandler httpHandler = WebHttpHandlerBuilder.applicationContext(this.applicationContext).build();
            // ...
            return httpHandler;
        }

    }
}
public final class WebHttpHandlerBuilder {
    private final List filters = new ArrayList<>();
    // 获取WebHttpHandlerBuilder对象
    public static WebHttpHandlerBuilder applicationContext(ApplicationContext context) {
        // 构造WebHttpHandlerBuilder对象，在参数上会获取
        // 容器中的webHandler名称的WebHandler对象，
        // 而这里获取的就是DispatcherHandler对象
        // 这个对象是如何创建的？
        // 1.2.1
        WebHttpHandlerBuilder builder = new WebHttpHandlerBuilder(
                context.getBean(WEB_HANDLER_BEAN_NAME, WebHandler.class), context);

        // 获取容器中所有的WebFilter类型的Bean对象
        List webFilters = context
                .getBeanProvider(WebFilter.class)
                .orderedStream()
                .collect(Collectors.toList());
        // 添加到了filters集合中
        builder.filters(filters -> filters.addAll(webFilters));
        // 获取容器中所有的WebExceptionHandler类型的异常处理句柄
        List exceptionHandlers = context
                .getBeanProvider(WebExceptionHandler.class)
                .orderedStream()
                .collect(Collectors.toList());
        builder.exceptionHandlers(handlers -> handlers.addAll(exceptionHandlers));

        context.getBeanProvider(HttpHandlerDecoratorFactory.class)
                .orderedStream()
                .forEach(builder::httpHandlerDecorator);

        try {
            builder.sessionManager(
                    context.getBean(WEB_SESSION_MANAGER_BEAN_NAME, WebSessionManager.class));
        }catch (NoSuchBeanDefinitionException ex) {
        }

        try {
            builder.codecConfigurer(
                    context.getBean(SERVER_CODEC_CONFIGURER_BEAN_NAME, ServerCodecConfigurer.class));
        }catch (NoSuchBeanDefinitionException ex) {
        }
        try {
            builder.localeContextResolver(
                    context.getBean(LOCALE_CONTEXT_RESOLVER_BEAN_NAME, LocaleContextResolver.class));
        } catch (NoSuchBeanDefinitionException ex) {
        }

        try {
            builder.forwardedHeaderTransformer(
                    context.getBean(FORWARDED_HEADER_TRANSFORMER_BEAN_NAME, ForwardedHeaderTransformer.class));
        } catch (NoSuchBeanDefinitionException ex) {
        }

        return builder;
    }
    public HttpHandler build() {
        // 注意这里将webHandler = DispatcherHandler保存到了
        // FilteringWebHandler对象中
        WebHandler decorated = new FilteringWebHandler(this.webHandler, this.filters);
        // 查看下面的类信息
        decorated = new ExceptionHandlingWebHandler(decorated,  this.exceptionHandlers);

        HttpWebHandlerAdapter adapted = new HttpWebHandlerAdapter(decorated);
        // ...
        return (this.httpHandlerDecorator != null ? this.httpHandlerDecorator.apply(adapted) : adapted);
    }
}
// --------------------------------------------------------------------------------
// 上面获取了WebHttpHandlerBuilder对象后调用build开始创建
// HttpWebHandlerAdapter对象
public class HttpWebHandlerAdapter extends WebHandlerDecorator implements HttpHandler {
    public HttpWebHandlerAdapter(WebHandler delegate) {
        super(delegate);
    }
}
public class WebHandlerDecorator implements WebHandler {
    // 通过上面的源码，知道了这个
    // delegate = ExceptionHandlingWebHandler
    private final WebHandler delegate;
    public WebHandlerDecorator(WebHandler delegate) {
        this.delegate = delegate;
    }
    public WebHandler getDelegate() {
        return this.delegate;
    }
}
// -------------------------------------------------------------------------------
public class FilteringWebHandler extends WebHandlerDecorator {
    private final DefaultWebFilterChain chain;
    // 这里传递过来的handler = DispatcherHandler
    public FilteringWebHandler(WebHandler handler, List filters) {
        super(handler);
        // 创建了过滤器链
        this.chain = new DefaultWebFilterChain(handler, filters);
    }
}
public class ExceptionHandlingWebHandler extends WebHandlerDecorator {
    private final List exceptionHandlers;
    public ExceptionHandlingWebHandler(WebHandler delegate, List handlers) {
        // 这里的delegate = FilteringWebHandler
        super(delegate);
        List handlersToUse = new ArrayList<>();
        handlersToUse.add(new CheckpointInsertingHandler());
        handlersToUse.addAll(handlers);
        this.exceptionHandlers = Collections.unmodifiableList(handlersToUse);
    }
}

通过上面的源码应该非常清楚HttpWebHandlerAdapter对象创建的过程及该对象都会写什么东西。

到此你应该清楚了，上面一开始说的getDelegate()方法返回的就是ExceptionHandlingWebHandler对象。

DispatcherHandler创建

public class WebFluxAutoConfiguration {
    @Configuration(proxyBeanMethods = false)
    @EnableConfigurationProperties(WebProperties.class)
    public static class EnableWebFluxConfiguration extends DelegatingWebFluxConfiguration {
    }
}

在这里的DelegatingWebFluxConfiguration的父类。

WebFluxConfigurationSupport中创建了webHandler名称的DispatcherHandler对象。

public class WebFluxConfigurationSupport implements ApplicationContextAware {
    @Bean
    public DispatcherHandler webHandler() {
        return new DispatcherHandler();
    }
}

到此HttpWebHandlerAdapter#handle中执行的getDelegate方法返回的是ExceptionHandlingWebHandler对象。

2、 委托类WebHandler执行

接下来就是执行ExceptionHandlingWebHandler的handle方法了。

public class ExceptionHandlingWebHandler extends WebHandlerDecorator {
    private final List exceptionHandlers;
    public Mono handle(ServerWebExchange exchange) {
        Mono completion;
        try {
            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;
    }
}
public class WebHandlerDecorator implements WebHandler {
    // 通过在上面的build知道该deletgate = FilteringWebHandler
    private final WebHandler delegate;
    public Mono handle(ServerWebExchange exchange) {
        return this.delegate.handle(exchange);
    }
}
public class FilteringWebHandler extends WebHandlerDecorator {
    private final DefaultWebFilterChain chain;
    public FilteringWebHandler(WebHandler handler, List filters) {
        // 这个handler = DispatcherHandler对象
        super(handler);
        this.chain = new DefaultWebFilterChain(handler, filters);
    }
    @Override
    public Mono handle(ServerWebExchange exchange) {
        // 执行所有的过滤器
        return this.chain.filter(exchange);
    }
}
public class DefaultWebFilterChain implements WebFilterChain {

    private final List allFilters;
    @Nullable
    private final WebFilter currentFilter;
    // handler = DispatcherHandler
    private final WebHandler handler;
    public DefaultWebFilterChain(WebHandler handler, List filters) {
        Assert.notNull(handler, "WebHandler is required");
        this.allFilters = Collections.unmodifiableList(filters);
        this.handler = handler;
        // 这里就是为了让所有的WebFilter串联起来，按照顺序执行
        DefaultWebFilterChain chain = initChain(filters, handler);
        this.currentFilter = chain.currentFilter;
        this.chain = chain.chain;
    }
    private static DefaultWebFilterChain initChain(List filters, WebHandler handler) {
        // 这里就相当于是最后执行的一个Chain了，因为第三个参数（currentFilter） = null
        // 在羡慕的filter方法中执行的时候判断了currentFilter如果为空就执行DispatcherHandler#handle方法
        // 这里大致的流程如下：
        DefaultWebFilterChain chain = new DefaultWebFilterChain(filters, handler, null, null);
        ListIterator iterator = filters.listIterator(filters.size());
        while (iterator.hasPrevious()) {
            chain = new DefaultWebFilterChain(filters, handler, iterator.previous(), chain);
        }
        return chain;
    }
    public Mono filter(ServerWebExchange exchange) {
        return Mono.defer(() ->
                this.currentFilter != null && this.chain != null ?
                        invokeFilter(this.currentFilter, this.chain, exchange) :
                        // 当过滤器都执行完了以后会执行DispatcherHandler调用
                        this.handler.handle(exchange));
    }
    private Mono invokeFilter(WebFilter current, DefaultWebFilterChain chain, ServerWebExchange exchange) {
        String currentName = current.getClass().getName();
        return current.filter(exchange, chain).checkpoint(currentName + " [DefaultWebFilterChain]");
    }
}

Webfilter: 1, 2, 3 三个WebFilter。

初始的chain： DefaultWebFilterChain chain = new DefaultWebFilterChain(filters, handler, null, null);

3： chain = DefaultWebFilterChain(filters，handler, 3，chain) 。

2: chain = DefaultWebFilterChain(filters，handler, 2，chain<3>) 。

1: chain = DefaultWebFilterChain(filters，handler, 1，chain<2>) 。

这样3个过滤器就串联在一起了。

WebFilter#filter实现： public Mono filter(ServerWebExchange exchange, WebFilterChain chain) { System.out.println("DemoFilter...") ; return chain.filter(exchange) ; } // 过滤器链执行过程： 1： chain.filter(exchange) ; => currentFilter.filter(exchange, chain) ;(执行的是当前WebFilter) 执行chain#filter，根据上面此时的chain = chain<2> 2: 依次类推。

3、 DispatcherHandler执行

public class DispatcherHandler implements WebHandler {
    public Mono 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));
    }
}

其实接下来的过程就和Spring WebMVC的执行大致相同。

  1. 查找HandlerMapping。
  2. 查找HandlerAdapter。
  3. 查找HandlerResultHandler。

通过HandlerAdapter调用处理程序的返回值被包装为HandlerResult，并传递给声称支持它的第一个HandlerResultHandler。下表显示了可用的HandlerResultHandler实现，所有这些实现都在WebFlux配置中声明：

4、 流程处理

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