Java實(shí)現(xiàn)異步編程的八種實(shí)現(xiàn)方式

一、前言

異步執(zhí)行對(duì)于開發(fā)者來說并不陌生，在實(shí)際的開發(fā)過程中，很多場(chǎng)景多會(huì)使用到異步，相比同步執(zhí)行，異步可以大大縮短請(qǐng)求鏈路耗時(shí)時(shí)間，比如：「發(fā)送短信、郵件、異步更新等」，這些都是典型的可以通過異步實(shí)現(xiàn)的場(chǎng)景。本文介紹了Java實(shí)現(xiàn)異步編程的八種方式

二、異步的八種實(shí)現(xiàn)方式

線程Thread

Future

異步框架CompletableFuture

Spring注解@Async

Spring ApplicationEvent事件

消息隊(duì)列

第三方異步框架，比如Hutool的ThreadUtil

Guava異步

三、什么是異步？

首先我們先看一個(gè)常見的用戶下單的場(chǎng)景：?

在同步操作中，我們執(zhí)行到「發(fā)送短信」的時(shí)候，我們必須等待這個(gè)方法徹底執(zhí)行完才能執(zhí)行「贈(zèng)送積分」這個(gè)操作，如果「贈(zèng)送積分」這個(gè)動(dòng)作執(zhí)行時(shí)間較長(zhǎng)，發(fā)送短信需要等待，這就是典型的同步場(chǎng)景。

實(shí)際上，發(fā)送短信和贈(zèng)送積分沒有任何的依賴關(guān)系，通過異步，我們可以實(shí)現(xiàn)贈(zèng)送積分和發(fā)送短信這兩個(gè)操作能夠同時(shí)進(jìn)行，比如：

這就是所謂的異步，是不是非常簡(jiǎn)單，下面就說說異步的幾種實(shí)現(xiàn)方式吧。

四、異步編程

4.1 線程異步

public?class?AsyncThread?extends?Thread?{

????@Override
????public?void?run()?{
????????System.out.println("Current?thread?name:"?+?Thread.currentThread().getName()?+?"?Send?email?success!");
????}

????public?static?void?main(String[]?args)?{
????????AsyncThread?asyncThread?=?new?AsyncThread();
????????asyncThread.run();
????}
}

當(dāng)然如果每次都創(chuàng)建一個(gè)Thread線程，頻繁的創(chuàng)建、銷毀，浪費(fèi)系統(tǒng)資源，我們可以采用線程池：

private?ExecutorService?executorService?=?Executors.newCachedThreadPool();

public?void?fun()?{
????executorService.submit(new?Runnable()?{
????????@Override
????????public?void?run()?{
????????????log.info("執(zhí)行業(yè)務(wù)邏輯...");
????????}
????});
}

可以將業(yè)務(wù)邏輯封裝到Runnable或Callable中，交由線程池來執(zhí)行。

4.2 Future異步

@Slf4j
public?class?FutureManager?{

????public?String?execute()?throws?Exception?{

????????ExecutorService?executor?=?Executors.newFixedThreadPool(1);
????????Future?future?=?executor.submit(new?Callable()?{
????????????@Override
????????????public?String?call()?throws?Exception?{

????????????????System.out.println("?---?task?start?---?");
????????????????Thread.sleep(3000);
????????????????System.out.println("?---?task?finish?---");
????????????????return?"this?is?future?execute?final?result!!!";
????????????}
????????});

????????//這里需要返回值時(shí)會(huì)阻塞主線程
????????String?result?=?future.get();
????????log.info("Future?get?result:?{}",?result);
????????return?result;
????}

????@SneakyThrows
????public?static?void?main(String[]?args)?{
????????FutureManager?manager?=?new?FutureManager();
????????manager.execute();
????}
}

輸出結(jié)果：

?---?task?start?---?
?---?task?finish?---
?Future?get?result:?this?is?future?execute?final?result!!!

4.2.1 Future的不足之處

Future的不足之處的包括以下幾點(diǎn)：

無法被動(dòng)接收異步任務(wù)的計(jì)算結(jié)果：雖然我們可以主動(dòng)將異步任務(wù)提交給線程池中的線程來執(zhí)行，但是待異步任務(wù)執(zhí)行結(jié)束之后，主線程無法得到任務(wù)完成與否的通知，它需要通過get方法主動(dòng)獲取任務(wù)執(zhí)行的結(jié)果。

2. Future件彼此孤立：有時(shí)某一個(gè)耗時(shí)很長(zhǎng)的異步任務(wù)執(zhí)行結(jié)束之后，你想利用它返回的結(jié)果再做進(jìn)一步的運(yùn)算，該運(yùn)算也會(huì)是一個(gè)異步任務(wù)，兩者之間的關(guān)系需要程序開發(fā)人員手動(dòng)進(jìn)行綁定賦予，F(xiàn)uture并不能將其形成一個(gè)任務(wù)流（pipeline），每一個(gè)Future都是彼此之間都是孤立的，所以才有了后面的CompletableFuture，CompletableFuture就可以將多個(gè)Future串聯(lián)起來形成任務(wù)流。

3. Futrue沒有很好的錯(cuò)誤處理機(jī)制：截止目前，如果某個(gè)異步任務(wù)在執(zhí)行發(fā)的過程中發(fā)生了異常，調(diào)用者無法被動(dòng)感知，必須通過捕獲get方法的異常才知曉異步任務(wù)執(zhí)行是否出現(xiàn)了錯(cuò)誤，從而在做進(jìn)一步的判斷處理。

4.3 CompletableFuture實(shí)現(xiàn)異步

public?class?CompletableFutureCompose?{

????/**
?????*?thenAccept子任務(wù)和父任務(wù)公用同一個(gè)線程
?????*/
????@SneakyThrows
????public?static?void?thenRunAsync()?{
????????CompletableFuture?cf1?=?CompletableFuture.supplyAsync(()?->?{
????????????System.out.println(Thread.currentThread()?+?"?cf1?do?something....");
????????????return?1;
????????});
????????CompletableFuture?cf2?=?cf1.thenRunAsync(()?->?{
????????????System.out.println(Thread.currentThread()?+?"?cf2?do?something...");
????????});
????????//等待任務(wù)1執(zhí)行完成
????????System.out.println("cf1結(jié)果->"?+?cf1.get());
????????//等待任務(wù)2執(zhí)行完成
????????System.out.println("cf2結(jié)果->"?+?cf2.get());
????}

????public?static?void?main(String[]?args)?{
????????thenRunAsync();
????}
}

我們不需要顯式使用ExecutorService，CompletableFuture 內(nèi)部使用了ForkJoinPool來處理異步任務(wù)，如果在某些業(yè)務(wù)場(chǎng)景我們想自定義自己的異步線程池也是可以的。

4.4 Spring的@Async異步

4.4.1 自定義異步線程池

/**
?*?線程池參數(shù)配置，多個(gè)線程池實(shí)現(xiàn)線程池隔離，@Async注解，默認(rèn)使用系統(tǒng)自定義線程池，可在項(xiàng)目中設(shè)置多個(gè)線程池，在異步調(diào)用的時(shí)候，指明需要調(diào)用的線程池名稱，比如：@Async("taskName")
@EnableAsync
@Configuration
public?class?TaskPoolConfig?{
????/**
?????*?自定義線程池
?????*
?????**/
????@Bean("taskExecutor")
????public?Executor?taskExecutor()?{
????????//返回可用處理器的Java虛擬機(jī)的數(shù)量?12
????????int?i?=?Runtime.getRuntime().availableProcessors();
????????System.out.println("系統(tǒng)最大線程數(shù)??：?"?+?i);
????????ThreadPoolTaskExecutor?executor?=?new?ThreadPoolTaskExecutor();
????????//核心線程池大小
????????executor.setCorePoolSize(16);
????????//最大線程數(shù)
????????executor.setMaxPoolSize(20);
????????//配置隊(duì)列容量，默認(rèn)值為Integer.MAX_VALUE
????????executor.setQueueCapacity(99999);
????????//活躍時(shí)間
????????executor.setKeepAliveSeconds(60);
????????//線程名字前綴
????????executor.setThreadNamePrefix("asyncServiceExecutor?-");
????????//設(shè)置此執(zhí)行程序應(yīng)該在關(guān)閉時(shí)阻止的最大秒數(shù)，以便在容器的其余部分繼續(xù)關(guān)閉之前等待剩余的任務(wù)完成他們的執(zhí)行
????????executor.setAwaitTerminationSeconds(60);
????????//等待所有的任務(wù)結(jié)束后再關(guān)閉線程池
????????executor.setWaitForTasksToCompleteOnShutdown(true);
????????return?executor;
????}
}

4.4.2 AsyncService

public?interface?AsyncService?{

????MessageResult?sendSms(String?callPrefix,?String?mobile,?String?actionType,?String?content);

????MessageResult?sendEmail(String?email,?String?subject,?String?content);
}

@Slf4j
@Service
public?class?AsyncServiceImpl?implements?AsyncService?{

????@Autowired
????private?IMessageHandler?mesageHandler;

????@Override
????@Async("taskExecutor")
????public?MessageResult?sendSms(String?callPrefix,?String?mobile,?String?actionType,?String?content)?{
????????try?{

????????????Thread.sleep(1000);
????????????mesageHandler.sendSms(callPrefix,?mobile,?actionType,?content);

????????}?catch?(Exception?e)?{
????????????log.error("發(fā)送短信異常?->?",?e)
????????}
????}
????
????@Override
????@Async("taskExecutor")
????public?sendEmail(String?email,?String?subject,?String?content)?{
????????try?{

????????????Thread.sleep(1000);
????????????mesageHandler.sendsendEmail(email,?subject,?content);

????????}?catch?(Exception?e)?{
????????????log.error("發(fā)送email異常?->?",?e)
????????}
????}
}

在實(shí)際項(xiàng)目中，使用@Async調(diào)用線程池，推薦等方式是是使用自定義線程池的模式，不推薦直接使用@Async直接實(shí)現(xiàn)異步。

4.5 Spring ApplicationEvent事件實(shí)現(xiàn)異步

4.5.1 定義事件

public?class?AsyncSendEmailEvent?extends?ApplicationEvent?{

????/**
?????*?郵箱
?????**/
????private?String?email;

???/**
?????*?主題
?????**/
????private?String?subject;

????/**
?????*?內(nèi)容
?????**/
????private?String?content;
??
????/**
?????*?接收者
?????**/
????private?String?targetUserId;

}

4.5.2 定義事件處理器

@Slf4j
@Component
public?class?AsyncSendEmailEventHandler?implements?ApplicationListener?{

????@Autowired
????private?IMessageHandler?mesageHandler;
????
????@Async("taskExecutor")
????@Override
????public?void?onApplicationEvent(AsyncSendEmailEvent?event)?{
????????if?(event?==?null)?{
????????????return;
????????}

????????String?email?=?event.getEmail();
????????String?subject?=?event.getSubject();
????????String?content?=?event.getContent();
????????String?targetUserId?=?event.getTargetUserId();
????????mesageHandler.sendsendEmailSms(email,?subject,?content,?targerUserId);
??????}
}

另外，可能有些時(shí)候采用ApplicationEvent實(shí)現(xiàn)異步的使用，當(dāng)程序出現(xiàn)異常錯(cuò)誤的時(shí)候，需要考慮補(bǔ)償機(jī)制，那么這時(shí)候可以結(jié)合Spring Retry重試來幫助我們避免這種異常造成數(shù)據(jù)不一致問題。

4.6 消息隊(duì)列

4.6.1 回調(diào)事件消息生產(chǎn)者

@Slf4j
@Component
public?class?CallbackProducer?{

????@Autowired
????AmqpTemplate?amqpTemplate;

????public?void?sendCallbackMessage(CallbackDTO?allbackDTO,?final?long?delayTimes)?{

????????log.info("生產(chǎn)者發(fā)送消息，callbackDTO，{}",?callbackDTO);

????????amqpTemplate.convertAndSend(CallbackQueueEnum.QUEUE_GENSEE_CALLBACK.getExchange(),?CallbackQueueEnum.QUEUE_GENSEE_CALLBACK.getRoutingKey(),?JsonMapper.getInstance().toJson(genseeCallbackDTO),?new?MessagePostProcessor()?{
????????????@Override
????????????public?Message?postProcessMessage(Message?message)?throws?AmqpException?{
????????????????//給消息設(shè)置延遲毫秒值，通過給消息設(shè)置x-delay頭來設(shè)置消息從交換機(jī)發(fā)送到隊(duì)列的延遲時(shí)間
????????????????message.getMessageProperties().setHeader("x-delay",?delayTimes);
????????????????message.getMessageProperties().setCorrelationId(callbackDTO.getSdkId());
????????????????return?message;
????????????}
????????});
????}
}

4.6.2 回調(diào)事件消息消費(fèi)者

@Slf4j
@Component
@RabbitListener(queues?=?"message.callback",?containerFactory?=?"rabbitListenerContainerFactory")
public?class?CallbackConsumer?{

????@Autowired
????private?IGlobalUserService?globalUserService;

????@RabbitHandler
????public?void?handle(String?json,?Channel?channel,?@Headers?Map?map)?throws?Exception?{

????????if?(map.get("error")?!=?null)?{
????????????//否認(rèn)消息
????????????channel.basicNack((Long)?map.get(AmqpHeaders.DELIVERY_TAG),?false,?true);
????????????return;
????????}

????????try?{
????????
????????????CallbackDTO?callbackDTO?=?JsonMapper.getInstance().fromJson(json,?CallbackDTO.class);
????????????//執(zhí)行業(yè)務(wù)邏輯
????????????globalUserService.execute(callbackDTO);
????????????//消息消息成功手動(dòng)確認(rèn)，對(duì)應(yīng)消息確認(rèn)模式acknowledge-mode:?manual
????????????channel.basicAck((Long)?map.get(AmqpHeaders.DELIVERY_TAG),?false);

????????}?catch?(Exception?e)?{
????????????log.error("回調(diào)失敗?->?{}",?e);
????????}
????}
}

4.7 ThreadUtil異步工具類

@Slf4j
public?class?ThreadUtils?{

????public?static?void?main(String[]?args)?{
????????for?(int?i?=?0;?i??{
????????????????ThreadLocalRandom?threadLocalRandom?=?ThreadLocalRandom.current();
????????????????int?number?=?threadLocalRandom.nextInt(20)?+?1;
????????????????System.out.println(number);
????????????});
????????????log.info("當(dāng)前第："?+?i?+?"個(gè)線程");
????????}

????????log.info("task?finish!");
????}
}

4.8 Guava異步

Guava的ListenableFuture顧名思義就是可以監(jiān)聽的Future，是對(duì)java原生Future的擴(kuò)展增強(qiáng)。我們知道Future表示一個(gè)異步計(jì)算任務(wù)，當(dāng)任務(wù)完成時(shí)可以得到計(jì)算結(jié)果。如果我們希望一旦計(jì)算完成就拿到結(jié)果展示給用戶或者做另外的計(jì)算，就必須使用另一個(gè)線程不斷的查詢計(jì)算狀態(tài)。這樣做，代碼復(fù)雜，而且效率低下。使用「Guava ListenableFuture」可以幫我們檢測(cè)Future是否完成了，不需要再通過get()方法苦苦等待異步的計(jì)算結(jié)果，如果完成就自動(dòng)調(diào)用回調(diào)函數(shù)，這樣可以減少并發(fā)程序的復(fù)雜度。

ListenableFuture是一個(gè)接口，它從jdk的Future接口繼承，添加了void addListener(Runnable listener, Executor executor)方法。

我們看下如何使用ListenableFuture。首先需要定義ListenableFuture的實(shí)例:

?ListeningExecutorService?executorService?=?MoreExecutors.listeningDecorator(Executors.newCachedThreadPool());
????????final?ListenableFuture?listenableFuture?=?executorService.submit(new?Callable()?{
????????????@Override
????????????public?Integer?call()?throws?Exception?{
????????????????log.info("callable?execute...")
????????????????TimeUnit.SECONDS.sleep(1);
????????????????return?1;
????????????}
????????});

首先通過MoreExecutors類的靜態(tài)方法listeningDecorator方法初始化一個(gè)ListeningExecutorService的方法，然后使用此實(shí)例的submit方法即可初始化ListenableFuture對(duì)象。

ListenableFuture要做的工作，在Callable接口的實(shí)現(xiàn)類中定義，這里只是休眠了1秒鐘然后返回一個(gè)數(shù)字1，有了ListenableFuture實(shí)例，可以執(zhí)行此Future并執(zhí)行Future完成之后的回調(diào)函數(shù)。

?Futures.addCallback(listenableFuture,?new?FutureCallback()?{
????@Override
????public?void?onSuccess(Integer?result)?{
????????//成功執(zhí)行...
????????System.out.println("Get?listenable?future's?result?with?callback?"?+?result);
????}

????@Override
????public?void?onFailure(Throwable?t)?{
????????//異常情況處理...
????????t.printStackTrace();
????}
});

那么，以上就是本期介紹的實(shí)現(xiàn)異步的8種方式了。

編輯：黃飛

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