springboot(六)——springboot与webflux结合初探

spring-cloud-gateway 的ReactorHttpHandlerAdapter

这几天看了看spring-cloud-gateway的请求处理流程，因为之前一直用的springboot1.x和spring4，一开始对spring-cloud-gateway的处理流程有点懵逼，找不到入口，后来跟了代码，在网上找了点资料，发现spring-cloud-gateway的入口在ReactorHttpHandlerAdapter的apply方法

public class ReactorHttpHandlerAdapter implements BiFunction<HttpServerRequest, HttpServerResponse, Mono<Void>> {

    private static final Log logger = HttpLogging.forLogName(ReactorHttpHandlerAdapter.class);


    private final HttpHandler httpHandler;
    public ReactorHttpHandlerAdapter(HttpHandler httpHandler) {
        Assert.notNull(httpHandler, "HttpHandler must not be null");
        this.httpHandler = httpHandler;
    }
    @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();
        }
    }

}

该方法的作用就是把接收到的HttpServerRequest或者最终需要返回的HttpServerResponse，包装转换为ReactorServerHttpRequest和ReactorServerHttpResponse。

spring-webflux

当然，这篇文章的主要内容不是谈论spring-cloud-gateway了，因为之前一直用的spring4，所以对spring5当中的反应式编程范式和webflux不太了解，所以先写个demo了解一下
第一步：引入相关pom,测试的相关pom根据自己的需要引入

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>


    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>io.projectreactor</groupId>
            <artifactId>reactor-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

第二步：创建一个HandlerFunction

public class TestFunction implements HandlerFunction<ServerResponse> {

    @Override
    public Mono<ServerResponse> handle(ServerRequest serverRequest) {
        return ServerResponse.ok().body(
                Mono.just(parse(serverRequest, "args1") + parse(serverRequest, "args2"))
                , Integer.class);
    }

    private int parse(final ServerRequest request, final String param) {
        return Integer.parseInt(request.queryParam(param).orElse("0"));
    }
}

第三步：注入一个RouterFunction

@Configuration
public class TestRouteFunction {

    @Bean
    public RouterFunction<ServerResponse> routerFunction() {
        return RouterFunctions.route(RequestPredicates.GET("/add"), new TestFunction());
    }
}

第四步：在webflux中，也可以使用之前的java注解的编程方式，我们也创建一个controller

@RestController
@RequestMapping("/api/test")
public class HelloController {

    @RequestMapping("/hello")
    public Mono<String> hello() {
        return Mono.just("hello world");
    }
}

第五步：创建启动类

@SpringBootApplication
public class Spring5DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(Spring5DemoApplication.class, args);
    }
}

第六步：启动项目，访问如下两个接口都可以

http://localhost:8080/api/test/hello
http://localhost:8080/add?args1=2&args2=3

和spring-boot结合

通过上面的例子，我们看到基本的两个类：HandlerFunction和RouterFunction，同时webflux有如下特性：

1. 异步非阻塞
2. 响应式(reactive)函数编程，纯lambda表达式
3. 不仅仅是在Servlet容器中tomcat/jetty中运行，同时支持NIO的Netty和Undertow中，实际项目中，我们往往与spring-boot项目结合，我们跟进代码可以看看spring-boot是在什么时候创建的server

一、SpringApplication

    public ConfigurableApplicationContext run(String... args) {
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
        configureHeadlessProperty();
        SpringApplicationRunListeners listeners = getRunListeners(args);
        listeners.starting();
        try {
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(
                    args);
            ConfigurableEnvironment environment = prepareEnvironment(listeners,
                    applicationArguments);
            configureIgnoreBeanInfo(environment);
            Banner printedBanner = printBanner(environment);
            context = createApplicationContext();
            exceptionReporters = getSpringFactoriesInstances(
                    SpringBootExceptionReporter.class,
                    new Class[] { ConfigurableApplicationContext.class }, context);
            prepareContext(context, environment, listeners, applicationArguments,
                    printedBanner);
            refreshContext(context);
            afterRefresh(context, applicationArguments);
            stopWatch.stop();
            if (this.logStartupInfo) {
                new StartupInfoLogger(this.mainApplicationClass)
                        .logStarted(getApplicationLog(), stopWatch);
            }
            listeners.started(context);
            callRunners(context, applicationArguments);
        }
        catch (Throwable ex) {
            handleRunFailure(context, ex, exceptionReporters, listeners);
            throw new IllegalStateException(ex);
        }

        try {
            listeners.running(context);
        }
        catch (Throwable ex) {
            handleRunFailure(context, ex, exceptionReporters, null);
            throw new IllegalStateException(ex);
        }
        return context;
    }

我们只分析入口，其它代码暂时不管，找到refreshContext(context);这一行进去

二、ReactiveWebServerApplicationContext的refresh()

    @Override
    public final void refresh() throws BeansException, IllegalStateException {
        try {
            super.refresh();
        }
        catch (RuntimeException ex) {
            stopAndReleaseReactiveWebServer();
            throw ex;
        }
    }

三、ReactiveWebServerApplicationContext的onRefresh()

    @Override
    protected void onRefresh() {
        super.onRefresh();
        try {
            createWebServer();
        }
        catch (Throwable ex) {
            throw new ApplicationContextException("Unable to start reactive web server",
                    ex);
        }
    }

四、看到这里我们就找到入口方法了：createWebServer(),跟进去，找到NettyReactiveWebServerFactory中创建webserver

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

看到ReactorHttpHandlerAdapter这个类想必特别亲切，在开篇说过是spring-cloud-gateway的入口，createHttpServer方法的细节暂时没有去学习了，后续有时间去深入了解下

结语

spring5的相关新特性也是在学习中，这一篇文章算是和springboot结合的入门吧，后续有时间再深入学习

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