springboot 使用webflux响应式开发教程（一）

什么是webFlux

左侧是传统的基于Servlet的Spring Web MVC框架，右侧是5.0版本新引入的基于Reactive Streams的Spring WebFlux框架，从上到下依次是Router Functions，WebFlux，Reactive Streams三个新组件。

Router Functions: 对标@Controller，@RequestMapping等标准的Spring MVC注解，提供一套函数式风格的API，用于创建Router，Handler和Filter。
WebFlux: 核心组件，协调上下游各个组件提供响应式编程支持。
Reactive Streams: 一种支持背压（Backpressure）的异步数据流处理标准，主流实现有RxJava和Reactor，Spring WebFlux默认集成的是Reactor。
在Web容器的选择上，Spring WebFlux既支持像Tomcat，Jetty这样的的传统容器（前提是支持Servlet 3.1 Non-Blocking IO API），又支持像Netty，Undertow那样的异步容器。不管是何种容器，Spring WebFlux都会将其输入输出流适配成Flux<DataBuffer>格式，以便进行统一处理。

值得一提的是，除了新的Router Functions接口，Spring WebFlux同时支持使用老的Spring MVC注解声明Reactive Controller。和传统的MVC Controller不同，Reactive Controller操作的是非阻塞的ServerHttpRequest和ServerHttpResponse，而不再是Spring MVC里的HttpServletRequest和HttpServletResponse。

    @GetMapping("/reactive/restaurants")
    public Flux<Restaurant> findAll() {
        return restaurantRepository.findAll();
    }

可以看到主要变化就是在 返回的类型上Flux<Restaurant>

Flux和Mono 是 Reactor 中的流数据类型，其中Flux会发送多次，Mono会发送0次或一次

使用webflux需要具备的基础是Reactive programming 的理解。
Reactor 的基础 和 熟练的java8 lambda使用

创建springboot应用
下面通过创建股票报价的demo来演示。

通过 https://start.spring.io 或idea自带功能创建springboot项目，groupId为io.spring.workshop,artifactId为 stock-quotes。

勾选 ReactiveWeb

修改 application.properties 配置文件，指定接口 8081

server.port=

启动应用，成功后控制台输出日志

日志显示使用Netty而不是tomcat，后续会使用Tomcat

股票报价生成
定义实体

@Data
public class Quote {
 
    private static final MathContext MATH_CONTEXT = new MathContext();
 
    private String ticker;
 
    private BigDecimal price;
 
    private Instant instant;
 
    public Quote() {
    }
 
    public Quote(String ticker, BigDecimal price) {
        this.ticker = ticker;
        this.price = price;
    }
 
    public Quote(String ticker, Double price) {
        this(ticker, new BigDecimal(price, MATH_CONTEXT));
    }
 
    @Override
    public String toString() {
        return "Quote{" +
                "ticker='" + ticker + '\'' +
                ", price=" + price +
                ", instant=" + instant +
                '}';
    }
}

定义生成器

@Component
public class QuoteGenerator {
 
    private final MathContext mathContext = new MathContext();
 
    private final Random random = new Random();
 
    private final List<Quote> prices = new ArrayList<>();
 
    /**
     * 生成行情数据
     */
    public QuoteGenerator() {
        this.prices.add(new Quote("CTXS", 82.26));
        this.prices.add(new Quote("DELL", 63.74));
        this.prices.add(new Quote("GOOG", 847.24));
        this.prices.add(new Quote("MSFT", 65.11));
        this.prices.add(new Quote("ORCL", 45.71));
        this.prices.add(new Quote("RHT", 84.29));
        this.prices.add(new Quote("VMW", 92.21));
    }
 
    public Flux<Quote> fetchQuoteStream(Duration period) {
 
        // 需要周期生成值并返回，使用 Flux.interval
        return Flux.interval(period)
                // In case of back-pressure, drop events
                .onBackpressureDrop()
                // For each tick, generate a list of quotes
                .map(this::generateQuotes)
                // "flatten" that List<Quote> into a Flux<Quote>
                .flatMapIterable(quotes -> quotes)
                .log("io.spring.workshop.stockquotes");
    }
 
    /**
     * Create quotes for all tickers at a single instant.
     */
    private List<Quote> generateQuotes(long interval) {
        final Instant instant = Instant.now();
        return prices.stream()
                .map(baseQuote -> {
                    BigDecimal priceChange = baseQuote.getPrice()
                            .multiply(new BigDecimal(0.05 * this.random.nextDouble()), this.mathContext);
                    Quote result = new Quote(baseQuote.getTicker(), baseQuote.getPrice().add(priceChange));
                    result.setInstant(instant);
                    return result;
                })
                .collect(Collectors.toList());
    }
}

使用webflux创建web应用

webflux的使用有两种方式，基于注解和函数式编程。这里使用函数式编程，先贴代码：

创建QuoteHandler

@Component
public class QuoteHandler {
 
    private final Flux<Quote> quoteStream;
 
    public QuoteHandler(QuoteGenerator quoteGenerator) {
        this.quoteStream = quoteGenerator.fetchQuoteStream(ofMillis()).share();
    }
 
    public Mono<ServerResponse> hello(ServerRequest request) {
        return ok().contentType(TEXT_PLAIN)
                .body(BodyInserters.fromObject("Hello Spring!"));
    }
 
    public Mono<ServerResponse> echo(ServerRequest request) {
        return ok().contentType(TEXT_PLAIN)
                .body(request.bodyToMono(String.class), String.class);
    }
 
    public Mono<ServerResponse> streamQuotes(ServerRequest request) {
        return ok()
                .contentType(APPLICATION_STREAM_JSON)
                .body(this.quoteStream, Quote.class);
    }
 
    public Mono<ServerResponse> fetchQuotes(ServerRequest request) {
        int size = Integer.parseInt(request.queryParam("size").orElse(""));
        return ok()
                .contentType(APPLICATION_JSON)
                .body(this.quoteStream.take(size), Quote.class);
    }
}

创建Router

@Configuration
public class QuoteRouter {
 
   @Bean
   public RouterFunction<ServerResponse> route(QuoteHandler quoteHandler) {
      return RouterFunctions
            .route(GET("/hello").and(accept(TEXT_PLAIN)), quoteHandler::hello)
            .andRoute(POST("/echo").and(accept(TEXT_PLAIN).and(contentType(TEXT_PLAIN))), quoteHandler::echo)
            .andRoute(GET("/quotes").and(accept(APPLICATION_JSON)), quoteHandler::fetchQuotes)
            .andRoute(GET("/quotes").and(accept(APPLICATION_STREAM_JSON)), quoteHandler::streamQuotes);
   }
}

需要注意的是在springboot中Handler和Router都需要打上@Configuration。

HTTP请求交由Router转发给对应的Handler，Handler处理请求，并返回Mono<ServerResponse>，这里的Router类似@RequestMapping，Handler类似Controller。这么理解非常容易。

运行项目，浏览器输入 http://localhost:8081/hello 或者 使用curl，即可收到 "Hello Spring!"的文本信息。

到目前为止，一个简单的webflux示例已经完成，但是还没有体现出它与传统模式有何不同。

下面我们来做一下测试：

$ curl http://localhost:8081/echo -i -d "WebFlux workshop" -H "Content-Type: text/plain"
HTTP/1.1  OK
transfer-encoding: chunked
Content-Type: text/plain
 
WebFlux workshop

还是没有区别T.T，看下一步。

$ curl http://localhost:8081/quotes -i -H "Accept: application/stream+json"
HTTP/1.1  OK
transfer-encoding: chunked
Content-Type: application/stream+json
 
{"ticker":"CTXS","price":82.77,"instant":"2018-05-15T06:45:51.261Z"}
{"ticker":"DELL","price":64.83,"instant":"2018-05-15T06:45:51.261Z"}
{"ticker":"GOOG","price":,"instant":"2018-05-15T06:45:51.261Z"}
{"ticker":"MSFT","price":67.3,"instant":"2018-05-15T06:45:51.261Z"}
{"ticker":"ORCL","price":48.1,"instant":"2018-05-15T06:45:51.261Z"}
{"ticker":"RHT","price":85.1,"instant":"2018-05-15T06:45:51.261Z"}
{"ticker":"VMW","price":92.24,"instant":"2018-05-15T06:45:51.261Z"}
-------------------------------无敌分割线-------------------------------------
{"ticker":"CTXS","price":85.7,"instant":"2018-05-15T06:45:52.260Z"}
{"ticker":"DELL","price":64.12,"instant":"2018-05-15T06:45:52.260Z"}
{"ticker":"GOOG","price":,"instant":"2018-05-15T06:45:52.260Z"}
{"ticker":"MSFT","price":67.9,"instant":"2018-05-15T06:45:52.260Z"}
{"ticker":"ORCL","price":46.43,"instant":"2018-05-15T06:45:52.260Z"}
{"ticker":"RHT","price":86.8,"instant":"2018-05-15T06:45:52.260Z"}
...

上面的分割线是为了易于分辨人为加上去的，我们看到返回结果每隔一秒刷新一次，不终止的话会一直返回数据，传统的Request/Response是一次请求，一次返回。

注意是设置了Header Accept: application/stream+json ，

如果将Header设置为 Accept: application/json ，只会得到一次Response。

写测试
springboot的test模块包含WebTestClient,可以用来对webflux服务端进行测试。

@RunWith(SpringRunner.class)
//  We create a `@SpringBootTest`, starting an actual server on a `RANDOM_PORT`
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class StockQuotesApplicationTests {
 
   // Spring Boot will create a `WebTestClient` for you,
   // already configure and ready to issue requests against "localhost:RANDOM_PORT"
   @Autowired
   private WebTestClient webTestClient;
 
   @Test
   public void fetchQuotes() {
      webTestClient
            // We then create a GET request to test an endpoint
            .get().uri("/quotes?size=20")
            .accept(MediaType.APPLICATION_JSON)
            .exchange()
            // and use the dedicated DSL to test assertions against the response
            .expectStatus().isOk()
            .expectHeader().contentType(MediaType.APPLICATION_JSON)
            .expectBodyList(Quote.class)
            .hasSize()
            // Here we check that all Quotes have a positive price value
            .consumeWith(allQuotes ->
                  assertThat(allQuotes.getResponseBody())
                        .allSatisfy(quote -> assertThat(quote.getPrice()).isPositive()));
   }
 
   @Test
   public void fetchQuotesAsStream() {
      List<Quote> result = webTestClient
            // We then create a GET request to test an endpoint
            .get().uri("/quotes")
            // this time, accepting "application/stream+json"
            .accept(MediaType.APPLICATION_STREAM_JSON)
            .exchange()
            // and use the dedicated DSL to test assertions against the response
            .expectStatus().isOk()
            .expectHeader().contentType(MediaType.APPLICATION_STREAM_JSON)
            .returnResult(Quote.class)
            .getResponseBody()
            .take()
            .collectList()
            .block();
 
      assertThat(result).allSatisfy(quote -> assertThat(quote.getPrice()).isPositive());
   }
}

参考文章：

https://docs.spring.io/spring-framework/docs/5.0.3.RELEASE/spring-framework-reference/web.html#web-reactive-server-functional
http://projectreactor.io/docs
https://www.ibm.com/developerworks/cn/java/spring5-webflux-reactive/index.html
https://blog.csdn.net/qq_34438958/article/details/78539234