自學Spring WebFlux（一）

一、什麼是響應式編程（Reactive Progarmming）

​響應式編程（Reactive Progarmming）是一種面向數據流和變化傳播的編程範式。

 

響應式編程主要處理二個問題：

1、異步非阻塞

2、流速控制

 

Reactive Progarmming模型：

 

二、響應式編程的優勢

Java 提供了兩種異步編程方式：

 

1、回調（Callbacks） ：異步方法沒有返回值，而是採用一個 callback 作爲參數（lambda 或匿名類），當結果出來後回調這個 callback。常見的例子比如 Swings 的 EventListener。

2、Futures（這個方法是阻塞的） ：異步方法 立即 返回一個 Future<T>，該異步方法要返回結果的是 T 類型，通過Future`封裝。這個結果並不是 *立刻* 可以拿到，而是等實際處理結束纔可用。比如， `ExecutorService 執行 Callable<T> 任務時會返回 Future 對象。

 

官方示例：

回調地獄 Callback Hell：獲取前5的建議，如果沒有建議，則採用默認的建議，傳統的回調寫法

userService.getFavorites(userId, new Callback<List<String>>() {public void onSuccess(List<String> list) {if (list.isEmpty()) {      suggestionService.getSuggestions(new Callback<List<Favorite>>() {public void onSuccess(List<Favorite> list) {          UiUtils.submitOnUiThread(() -> {            list.stream()                .limit(5)                .forEach(uiList::show);            });        }public void onError(Throwable error) {          UiUtils.errorPopup(error);        }      });    } else {      list.stream()          .limit(5)          .forEach(favId -> favoriteService.getDetails(favId,new Callback<Favorite>() {public void onSuccess(Favorite details) {                UiUtils.submitOnUiThread(() -> uiList.show(details));              }public void onError(Throwable error) {                UiUtils.errorPopup(error);              }            }          ));    }  }public void onError(Throwable error) {    UiUtils.errorPopup(error);  }});

Reactor的寫法

userService.getFavorites(userId).flatMap(favoriteService::getDetails).switchIfEmpty(suggestionService.getSuggestions()).take(5).publishOn(UiUtils.uiThreadScheduler()).subscribe(uiList::show, UiUtils::errorPopup);

Reactor 中增加超時控制的例子

userService.getFavorites(userId)// 數據在800ms內獲得           .timeout(Duration.ofMillis(800))// 如果超時/異常，從緩存中獲取           .onErrorResume(cacheService.cachedFavoritesFor(userId))           .flatMap(favoriteService::getDetails)           .switchIfEmpty(suggestionService.getSuggestions())           .take(5)           .publishOn(UiUtils.uiThreadScheduler())           .subscribe(uiList::show, UiUtils::errorPopup);

CompletableFuture的寫法（異步阻塞）

CompletableFuture<List<String>> ids = ifhIds();CompletableFuture<List<String>> result = ids.thenComposeAsync(l -> {        Stream<CompletableFuture<String>> zip =                        l.stream().map(i -> {                                                 CompletableFuture<String> nameTask = ifhName(i);                                                 CompletableFuture<Integer> statTask = ifhStat(i);                                                 return nameTask.thenCombineAsync(statTask, 
(name, stat) -> "Name " + name + " has stats " + stat);                                         });        List<CompletableFuture<String>> combinationList = zip.collect(Collectors.toList());        CompletableFuture<String>[] combinationArray = combinationList.toArray(
new CompletableFuture[combinationList.size()]);        CompletableFuture<Void> allDone = CompletableFuture.allOf(combinationArray);        return allDone.thenApply(v -> combinationList.stream() .map(CompletableFuture::join)                                                               .collect(Collectors.toList()));});List<String> results = result.join();assertThat(results).contains(                                "Name NameJoe has stats 103",                                "Name NameBart has stats 104",                                "Name NameHenry has stats 105",                                "Name NameNicole has stats 106",                                "Name NameABSLAJNFOAJNFOANFANSF has stats 121");

Reactor 實現與 Future 同樣功能的代碼

Flux<String> ids = ifhrIds();Flux<String> combinations =                ids.flatMap(id -> {                        Mono<String> nameTask = ifhrName(id);                        Mono<Integer> statTask = ifhrStat(id);return nameTask.zipWith(statTask,                                        (name, stat) -> "Name " + name + " has stats " + stat);                });Mono<List<String>> result = combinations.collectList();List<String> results = result.block();assertThat(results).containsExactly("Name NameJoe has stats 103","Name NameBart has stats 104","Name NameHenry has stats 105","Name NameNicole has stats 106","Name NameABSLAJNFOAJNFOANFANSF has stats 121");

你可以通過代碼對比，發現Reactor的代碼可讀性、可編排性更強、並且提供了背壓的支持。單次請求的處理耗時並不能得到有效提升，但是你可以用固定數量的線程和較少的內存實現擴展

 

三、Reactor基礎特性

Reactor 引入了實現 Publisher 的響應式類 Flux 和 Mono，以及豐富的操作方式。一個 Flux 對象代表一個包含 0..N 個元素的響應式序列，而一個 Mono 對象代表一個包含 零/一個（0..1）元素的結果。

 

Flux 對象代表一個包含 0..N 個元素的響應式序列

 

 

Mono 對象代表一個包含 零/一個（0..1）元素的結果

看完這篇文章，你應該要對Reactor有個基礎認知，爲後期的Spring WebFlux的實戰打下基礎，talk is cheap, show me the code，like 

@RunWith(SpringRunner.class)@SpringBootTest(classes = SpiderConfigApplication.class)@Slf4jpublic class ProductInfoControllerTest {​/**     * webflux test demo     */    @Testpublic void testDemo() {        log.info("getProductInfoByProductCode result is {}", WebClient                .create()                .get()                .uri("http://localhost:20501/product/getProductInfoByProductCode?productCode={productCode}", 
"PC000014")                .retrieve()                .bodyToMono(DataResult.class)                .block()                .feignData());    }​​/**     * 測試字段冗餘問題     */    @Testpublic void testEnv() {        log.info("getChannelVerifyInfo result is {}", WebClient                .create()                .get()                .uri("http://localhost:20501/product/getChannelVerifyInfo/{channelId}", 1)                .retrieve()                .bodyToMono(DataResult.class)                .block()                .feignData());​        log.info("getChannelInfoByCodeAndPlateform result is {}", WebClient                .create()                .get()                .uri(uriBuilder ->                        uriBuilder                                .scheme("http")                                .host("localhost")                                .port(20501)                                .path("/product/getChannelInfoByCodeAndPlateform")                                .queryParam("productCode", "3")                                .queryParam("plateform", 2)                                .build())                .retrieve()                .bodyToMono(DataResult.class)                .block()                .feignData());​    }​/**     * 需要模擬文件上傳     */    @Testpublic void testUploadLimit200() throws MalformedURLException {        MultiValueMap<String, Object> parts = new LinkedMultiValueMap<>();        parts.add("file", new UrlResource(" file:///D:\\參數文件導入模板.xlsx"));        log.info("importCustomParameters result is {}", WebClient                .create()                .post()                .uri("http://localhost:20501/product/importCustomParameters")                .contentType(MediaType.MULTIPART_FORM_DATA)                .body(BodyInserters.fromMultipartData(parts))                .retrieve()                .bodyToMono(DataResult.class)                .block()                .feignData());    }

 

參考： 

https://projectreactor.io/

https://blog.csdn.net/get_set/article/details/79480233