Spring boot加载REACTIVE源码分析

一，加载REACTIVE相关自动配置

spring boot通过判断含org.springframework.web.reactive.DispatcherHandler字节文件就确定程序类型是REACTIVE，然后加载上下文类org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext，看下面代码

private WebApplicationType deduceWebApplicationType() {
        if (ClassUtils.isPresent("org.springframework.web.reactive.DispatcherHandler", (ClassLoader)null) && !ClassUtils.isPresent("org.springframework.web.servlet.DispatcherServlet", (ClassLoader)null) && !ClassUtils.isPresent("org.glassfish.jersey.server.ResourceConfig", (ClassLoader)null)) {
            return WebApplicationType.REACTIVE;
        } else {
            String[] var1 = WEB_ENVIRONMENT_CLASSES;
            int var2 = var1.length;

            for(int var3 = 0; var3 < var2; ++var3) {
                String className = var1[var3];
                if (!ClassUtils.isPresent(className, (ClassLoader)null)) {
                    return WebApplicationType.NONE;
                }
            }

            return WebApplicationType.SERVLET;
        }
    }

当程序类型是REACTIVE，spring boot首先就会加载自身的自动配置类org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration。如果找到HttpServer.clas而且又没有自己实现的ReactiveWebServerFactory.class就应用spring boot自带的nettyReactiveWebServerFactory对象。如果会用jetty或tomcat就引用有Server.class或Tomcat.class第三方包。

@AutoConfigureOrder(-2147483648)
@Configuration
@ConditionalOnClass({ReactiveHttpInputMessage.class})
@ConditionalOnWebApplication(
    type = Type.REACTIVE
)
@EnableConfigurationProperties({ServerProperties.class})
@Import({ReactiveWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class, EmbeddedTomcat.class, EmbeddedJetty.class, EmbeddedUndertow.class, EmbeddedNetty.class})
public class ReactiveWebServerFactoryAutoConfiguration {
    public ReactiveWebServerFactoryAutoConfiguration() {
    }

......................................

abstract class ReactiveWebServerFactoryConfiguration {
    ReactiveWebServerFactoryConfiguration() {
    }

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

        @Bean
        public NettyReactiveWebServerFactory nettyReactiveWebServerFactory() {
            return new NettyReactiveWebServerFactory();
        }
    }

应用程序没有提供WebFluxConfigurationSupport的实例，spring boot就会加载自身的自动配置类org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration。加载对象有webHandler（org.springframework.web.reactive.DispatcherHandler）等

@Configuration
@ConditionalOnWebApplication(
    type = Type.REACTIVE
)
@ConditionalOnClass({WebFluxConfigurer.class})
@ConditionalOnMissingBean({WebFluxConfigurationSupport.class})
@AutoConfigureAfter({ReactiveWebServerFactoryAutoConfiguration.class, CodecsAutoConfiguration.class, ValidationAutoConfiguration.class})
@AutoConfigureOrder(-2147483638)
public class WebFluxAutoConfiguration {

应用程序没有提供HttpHandler的实例，spring boot就会加载自身的自动配置类org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration，加载对象httpHandler（org.springframework.web.server.adapter.HttpWebHandlerAdapter）。

@Configuration
@ConditionalOnClass({DispatcherHandler.class, HttpHandler.class})
@ConditionalOnWebApplication(
    type = Type.REACTIVE
)
@ConditionalOnMissingBean({HttpHandler.class})
@AutoConfigureAfter({WebFluxAutoConfiguration.class})
@AutoConfigureOrder(-2147483638)
public class HttpHandlerAutoConfiguration {
    public HttpHandlerAutoConfiguration() {
    }

    @Configuration
    public static class AnnotationConfig {
        private ApplicationContext applicationContext;

        public AnnotationConfig(ApplicationContext applicationContext) {
            this.applicationContext = applicationContext;
        }

        @Bean
        public HttpHandler httpHandler() {
            return WebHttpHandlerBuilder.applicationContext(this.applicationContext).build();
        }
    }
}

二，创建REACTIVE内嵌服务器

WebServer在org.springframework.boot.web.reactive.context.ReactiveWebServerApplicationContext创建。依赖的HttpHandler实例上面已说明如果创建的。

org.springframework.boot.web.reactive.context.ReactiveWebServerApplicationContext
 
   protected void onRefresh() {
        super.onRefresh();

        try {
            this.createWebServer();
        } catch (Throwable var2) {
            throw new ApplicationContextException("Unable to start reactive web server", var2);
        }
    }

    private void createWebServer() {
    　　WebServer localServer = this.webServer;
    　　if (localServer == null) {
       　　this.webServer = this.getWebServerFactory().getWebServer(this.getHttpHandler());
    　　}

    　　this.initPropertySources();
    }

org.springframework.boot.web.embedded.netty.NettyReactiveWebServerFactory

    public WebServer getWebServer(HttpHandler httpHandler) {
        HttpServer httpServer = this.createHttpServer();
        ReactorHttpHandlerAdapter handlerAdapter = new ReactorHttpHandlerAdapter(httpHandler);
        return new NettyWebServer(httpServer, handlerAdapter, this.lifecycleTimeout);
    }

三，Annotated Controllers与Functional Endpoints

spring webflux处理http请求有两种编程模式，分别是annotated controllers和functional endpoints，annotated controllers与spring mvc类似。它们都调用HttpHandler实现org.springframework.web.server.adapter.HttpWebHandlerAdapter的handle方法。

handle:183, HttpWebHandlerAdapter (org.springframework.web.server.adapter)
apply:75, ReactorHttpHandlerAdapter (org.springframework.http.server.reactive)
apply:40, ReactorHttpHandlerAdapter (org.springframework.http.server.reactive)
applyHandler:380, ChannelOperations (reactor.ipc.netty.channel)
onHandlerStart:407, HttpServerOperations (reactor.ipc.netty.http.server)
run:-1, 1927250759 (reactor.ipc.netty.channel.ContextHandler$$Lambda$524)
safeExecute$$$capture:163, AbstractEventExecutor (io.netty.util.concurrent)
safeExecute:-1, AbstractEventExecutor (io.netty.util.concurrent)
 - Async stack trace
addTask:-1, SingleThreadEventExecutor (io.netty.util.concurrent)
execute:765, SingleThreadEventExecutor (io.netty.util.concurrent)
createOperations:249, ContextHandler (reactor.ipc.netty.channel)
channelRead:136, HttpServerHandler (reactor.ipc.netty.http.server)
invokeChannelRead:362, AbstractChannelHandlerContext (io.netty.channel)
invokeChannelRead:348, AbstractChannelHandlerContext (io.netty.channel)
fireChannelRead:340, AbstractChannelHandlerContext (io.netty.channel)
fireChannelRead:438, CombinedChannelDuplexHandler$DelegatingChannelHandlerContext (io.netty.channel)
fireChannelRead:310, ByteToMessageDecoder (io.netty.handler.codec)
channelRead:284, ByteToMessageDecoder (io.netty.handler.codec)
channelRead:253, CombinedChannelDuplexHandler (io.netty.channel)
invokeChannelRead:362, AbstractChannelHandlerContext (io.netty.channel)
invokeChannelRead:348, AbstractChannelHandlerContext (io.netty.channel)
fireChannelRead:340, AbstractChannelHandlerContext (io.netty.channel)
channelRead:1434, DefaultChannelPipeline$HeadContext (io.netty.channel)
invokeChannelRead:362, AbstractChannelHandlerContext (io.netty.channel)
invokeChannelRead:348, AbstractChannelHandlerContext (io.netty.channel)
fireChannelRead:965, DefaultChannelPipeline (io.netty.channel)
read:163, AbstractNioByteChannel$NioByteUnsafe (io.netty.channel.nio)
processSelectedKey:628, NioEventLoop (io.netty.channel.nio)
processSelectedKeysOptimized:563, NioEventLoop (io.netty.channel.nio)
processSelectedKeys:480, NioEventLoop (io.netty.channel.nio)
run:442, NioEventLoop (io.netty.channel.nio)
run:884, SingleThreadEventExecutor$5 (io.netty.util.concurrent)
run:745, Thread (java.lang)

他们也调用handle:149, DispatcherHandler (org.springframework.web.reactive)，但最后他们分别调用BookController或BookHandler，看下面不同调用栈：

annotated controllers
getBookById:19, BookController (com.javaworld.webflux.bookservice.web)
invoke0:-1, NativeMethodAccessorImpl (sun.reflect)
invoke:62, NativeMethodAccessorImpl (sun.reflect)
invoke:43, DelegatingMethodAccessorImpl (sun.reflect)
invoke:498, Method (java.lang.reflect)
doInvoke:243, InvocableHandlerMethod (org.springframework.web.reactive.result.method)
lambda$invoke$0:138, InvocableHandlerMethod (org.springframework.web.reactive.result.method)
apply:-1, 595198211 (org.springframework.web.reactive.result.method.InvocableHandlerMethod$$Lambda$652)
onNext:118, MonoFlatMap$FlatMapMain (reactor.core.publisher)
complete:1083, Operators$MonoSubscriber (reactor.core.publisher)
signal:247, MonoZip$ZipCoordinator (reactor.core.publisher)

....................................................

functional endpoints
findById:24, BookHandler (com.javaworld.webflux.bookservice.web)
handle:-1, 953080701 (com.javaworld.webflux.bookservice.web.BookRouter$$Lambda$437)
handle:61, HandlerFunctionAdapter (org.springframework.web.reactive.function.server.support)
invokeHandler:168, DispatcherHandler (org.springframework.web.reactive)
lambda$handle$1:160, DispatcherHandler (org.springframework.web.reactive)
apply:-1, 1795086753 (org.springframework.web.reactive.DispatcherHandler$$Lambda$550)
onNext:118, MonoFlatMap$FlatMapMain (reactor.core.publisher)
onNext:67, FluxSwitchIfEmpty$SwitchIfEmptySubscriber (reactor.core.publisher)
onNext:76, MonoNext$NextSubscriber (reactor.core.publisher)

参考资料

spring webflux reference

Mastering Spring framework 5, Part 2: Spring WebFlux