【源码分析-Spring Boot】-14.Spring Boot WebFlux Server 装配及启动

Spring Boot WebFlux：【从零开始学Spring Boot】-15.Spring Boot WebFlux路由

1.Webflux Server 如何启动？

使用 webflux 时，默认的 applicationContext 为 AnnotationConfigReactiveWebServerApplicationContext

protected ConfigurableApplicationContext createApplicationContext() {
    Class<?> contextClass = this.applicationContextClass;
    if (contextClass == null) {
        try {
            switch (this.webApplicationType) {
                case SERVLET:
                    contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
                    break;
                case REACTIVE:
                    contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
                    break;
                default:
                    contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
            }
        }
        catch (ClassNotFoundException ex) {
            throw new IllegalStateException(
                "Unable create a default ApplicationContext, please specify an ApplicationContextClass", ex);
        }
    }
    return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}

所以在 AnnotationConfigReactiveWebServerApplicationContext 中进行初始化和启动

2.Webflux 默认 Server 为何是 Netty？

先看下 spring-boot-starter-webflux 的依赖结构

在 spring-boot-autoconfigure/spring.factories 中有一个自动装配的类 ReactiveWebServerFactoryAutoConfiguration

它的内容如下

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(ReactiveHttpInputMessage.class)
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.REACTIVE)
@EnableConfigurationProperties(ServerProperties.class)
@Import({ ReactiveWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
         ReactiveWebServerFactoryConfiguration.EmbeddedTomcat.class,
         ReactiveWebServerFactoryConfiguration.EmbeddedJetty.class,
         ReactiveWebServerFactoryConfiguration.EmbeddedUndertow.class,
         ReactiveWebServerFactoryConfiguration.EmbeddedNetty.class })
public class ReactiveWebServerFactoryAutoConfiguration {

    @Bean
    public ReactiveWebServerFactoryCustomizer reactiveWebServerFactoryCustomizer(ServerProperties serverProperties) {
        return new ReactiveWebServerFactoryCustomizer(serverProperties);
    }

    @Bean
    @ConditionalOnClass(name = "org.apache.catalina.startup.Tomcat")
    public TomcatReactiveWebServerFactoryCustomizer tomcatReactiveWebServerFactoryCustomizer(
        ServerProperties serverProperties) {
        return new TomcatReactiveWebServerFactoryCustomizer(serverProperties);
    }

    @Bean
    @ConditionalOnMissingBean
    @ConditionalOnProperty(value = "server.forward-headers-strategy", havingValue = "framework")
    public ForwardedHeaderTransformer forwardedHeaderTransformer() {
        return new ForwardedHeaderTransformer();
    }

    /**
    * Registers a {@link WebServerFactoryCustomizerBeanPostProcessor}. Registered via
    * {@link ImportBeanDefinitionRegistrar} for early registration.
    */
    public static class BeanPostProcessorsRegistrar implements ImportBeanDefinitionRegistrar, BeanFactoryAware {

        private ConfigurableListableBeanFactory beanFactory;

        @Override
        public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
            if (beanFactory instanceof ConfigurableListableBeanFactory) {
                this.beanFactory = (ConfigurableListableBeanFactory) beanFactory;
            }
        }

        @Override
        public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
            if (this.beanFactory == null) {
                return;
            }
            registerSyntheticBeanIfMissing(registry, "webServerFactoryCustomizerBeanPostProcessor",
                                           WebServerFactoryCustomizerBeanPostProcessor.class);
        }

        private void registerSyntheticBeanIfMissing(BeanDefinitionRegistry registry, String name, Class<?> beanClass) {
            if (ObjectUtils.isEmpty(this.beanFactory.getBeanNamesForType(beanClass, true, false))) {
                RootBeanDefinition beanDefinition = new RootBeanDefinition(beanClass);
                beanDefinition.setSynthetic(true);
                registry.registerBeanDefinition(name, beanDefinition);
            }
        }
    }
}

它里面通过 @Import 分别引入了 EmbeddedTomcat、EmbeddedJetty、EmbeddedUndertow、EmbeddedNetty，它们都是 ReactiveWebServerFactoryConfiguration 的内部类

abstract class ReactiveWebServerFactoryConfiguration {

    @Configuration(proxyBeanMethods = false)
    @ConditionalOnMissingBean(ReactiveWebServerFactory.class)
    @ConditionalOnClass({ HttpServer.class })
    static class EmbeddedNetty {

        @Bean
        @ConditionalOnMissingBean
        ReactorResourceFactory reactorServerResourceFactory() {
            return new ReactorResourceFactory();
        }

        @Bean
        NettyReactiveWebServerFactory nettyReactiveWebServerFactory(ReactorResourceFactory resourceFactory,
                                                                    ObjectProvider<NettyRouteProvider> routes, ObjectProvider<NettyServerCustomizer> serverCustomizers) {
            NettyReactiveWebServerFactory serverFactory = new NettyReactiveWebServerFactory();
            serverFactory.setResourceFactory(resourceFactory);
            routes.orderedStream().forEach(serverFactory::addRouteProviders);
            serverFactory.getServerCustomizers().addAll(serverCustomizers.orderedStream().collect(Collectors.toList()));
            return serverFactory;
        }

    }

    @Configuration(proxyBeanMethods = false)
    @ConditionalOnMissingBean(ReactiveWebServerFactory.class)
    @ConditionalOnClass({ org.apache.catalina.startup.Tomcat.class })
    static class EmbeddedTomcat {

        @Bean
        TomcatReactiveWebServerFactory tomcatReactiveWebServerFactory(
            ObjectProvider<TomcatConnectorCustomizer> connectorCustomizers,
            ObjectProvider<TomcatContextCustomizer> contextCustomizers,
            ObjectProvider<TomcatProtocolHandlerCustomizer<?>> protocolHandlerCustomizers) {
            TomcatReactiveWebServerFactory factory = new TomcatReactiveWebServerFactory();
            factory.getTomcatConnectorCustomizers()
                .addAll(connectorCustomizers.orderedStream().collect(Collectors.toList()));
            factory.getTomcatContextCustomizers()
                .addAll(contextCustomizers.orderedStream().collect(Collectors.toList()));
            factory.getTomcatProtocolHandlerCustomizers()
                .addAll(protocolHandlerCustomizers.orderedStream().collect(Collectors.toList()));
            return factory;
        }

    }

    @Configuration(proxyBeanMethods = false)
    @ConditionalOnMissingBean(ReactiveWebServerFactory.class)
    @ConditionalOnClass({ org.eclipse.jetty.server.Server.class })
    static class EmbeddedJetty {

        @Bean
        @ConditionalOnMissingBean
        JettyResourceFactory jettyServerResourceFactory() {
            return new JettyResourceFactory();
        }

        @Bean
        JettyReactiveWebServerFactory jettyReactiveWebServerFactory(JettyResourceFactory resourceFactory,
                                                                    ObjectProvider<JettyServerCustomizer> serverCustomizers) {
            JettyReactiveWebServerFactory serverFactory = new JettyReactiveWebServerFactory();
            serverFactory.getServerCustomizers().addAll(serverCustomizers.orderedStream().collect(Collectors.toList()));
            serverFactory.setResourceFactory(resourceFactory);
            return serverFactory;
        }

    }

    @Configuration(proxyBeanMethods = false)
    @ConditionalOnMissingBean(ReactiveWebServerFactory.class)
    @ConditionalOnClass({ Undertow.class })
    static class EmbeddedUndertow {

        @Bean
        UndertowReactiveWebServerFactory undertowReactiveWebServerFactory(
            ObjectProvider<UndertowBuilderCustomizer> builderCustomizers) {
            UndertowReactiveWebServerFactory factory = new UndertowReactiveWebServerFactory();
            factory.getBuilderCustomizers().addAll(builderCustomizers.orderedStream().collect(Collectors.toList()));
            return factory;
        }
    }
}

它们生效的条件分别是：

• EmbeddedTomcat： @ConditionalOnClass – Tomcat.class(apache)
• EmbeddedJetty： @ConditionalOnClass – Server.class(jetty)
• EmbeddedUndertow： @ConditionalOnClass – Undertow.class
• EmbeddedNetty： @ConditionalOnClass – HttpServer.class

结合上面的依赖分析，spring-boot-starter-webflux 中依赖了 reactor-netty.jar，而 HttpServer.class 恰好在 reactor-netty.jar 包中，所以 netty 生效。最终使用 EmbeddedNetty 启动服务。