[線程池]Springboot如何使用線程池

2023-03-16 23:06:38 來源：騰訊云

本文帶你快速了解@Async注解的用法，包括異步方法無返回值、有返回值，最后總結(jié)了@Async注解失效的幾個(gè)坑。

在 SpringBoot 應(yīng)用中，經(jīng)常會(huì)遇到在一個(gè)接口中，同時(shí)做事情1，事情2，事情3，如果同步執(zhí)行的話，則本次接口時(shí)間取決于事情1 2 3執(zhí)行時(shí)間之和；如果三件事同時(shí)執(zhí)行，則本次接口時(shí)間取決于事情1 2 3執(zhí)行時(shí)間最長的那個(gè)，合理使用多線程，可以大大縮短接口時(shí)間。那么在 SpringBoot 應(yīng)用中如何優(yōu)雅的使用多線程呢？

Don"t bb, show me code.

(相關(guān)資料圖)

快速使用

SpringBoot應(yīng)用中需要添加@EnableAsync注解，來開啟異步調(diào)用，一般還會(huì)配置一個(gè)線程池，異步的方法交給特定的線程池完成，如下：

@Configuration@EnableAsyncpublic class AsyncConfiguration {    @Bean("doSomethingExecutor")    public Executor doSomethingExecutor() {        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();        // 核心線程數(shù)：線程池創(chuàng)建時(shí)候初始化的線程數(shù)        executor.setCorePoolSize(10);        // 最大線程數(shù)：線程池最大的線程數(shù)，只有在緩沖隊(duì)列滿了之后才會(huì)申請(qǐng)超過核心線程數(shù)的線程        executor.setMaxPoolSize(20);        // 緩沖隊(duì)列：用來緩沖執(zhí)行任務(wù)的隊(duì)列        executor.setQueueCapacity(500);        // 允許線程的空閑時(shí)間60秒：當(dāng)超過了核心線程之外的線程在空閑時(shí)間到達(dá)之后會(huì)被銷毀        executor.setKeepAliveSeconds(60);        // 線程池名的前綴：設(shè)置好了之后可以方便我們定位處理任務(wù)所在的線程池        executor.setThreadNamePrefix("do-something-");        // 緩沖隊(duì)列滿了之后的拒絕策略：由調(diào)用線程處理（一般是主線程）        executor.setRejectedExecutionHandler(new ThreadPoolExecutor.DiscardPolicy());        executor.initialize();        return executor;    }}

使用的方式非常簡單，在需要異步的方法上加@Async注解

@RestControllerpublic class AsyncController {    @Autowired    private AsyncService asyncService;    @GetMapping("/open/something")    public String something() {        int count = 10;        for (int i = 0; i < count; i++) {            asyncService.doSomething("index = " + i);        }        lon        return "success";    }}@Slf4j@Servicepublic class AsyncService {    // 指定使用beanname為doSomethingExecutor的線程池    @Async("doSomethingExecutor")    public String doSomething(String message) {        log.info("do something, message={}", message);        try {            Thread.sleep(1000);        } catch (InterruptedException e) {            log.error("do something error: ", e);        }        return message;    }}

訪問：127.0.0.1:8080/open/something，日志如下

2020-04-19 23:42:42.486  INFO 21168 --- [io-8200-exec-17] x.g.b.system.controller.AsyncController  : do something end, time 8 milliseconds2020-04-19 23:42:42.488  INFO 21168 --- [ do-something-1] x.gits.boot.system.service.AsyncService  : do something, message=index = 02020-04-19 23:42:42.488  INFO 21168 --- [ do-something-5] x.gits.boot.system.service.AsyncService  : do something, message=index = 42020-04-19 23:42:42.488  INFO 21168 --- [ do-something-4] x.gits.boot.system.service.AsyncService  : do something, message=index = 32020-04-19 23:42:42.488  INFO 21168 --- [ do-something-6] x.gits.boot.system.service.AsyncService  : do something, message=index = 52020-04-19 23:42:42.488  INFO 21168 --- [ do-something-9] x.gits.boot.system.service.AsyncService  : do something, message=index = 82020-04-19 23:42:42.488  INFO 21168 --- [ do-something-8] x.gits.boot.system.service.AsyncService  : do something, message=index = 72020-04-19 23:42:42.488  INFO 21168 --- [do-something-10] x.gits.boot.system.service.AsyncService  : do something, message=index = 92020-04-19 23:42:42.488  INFO 21168 --- [ do-something-7] x.gits.boot.system.service.AsyncService  : do something, message=index = 62020-04-19 23:42:42.488  INFO 21168 --- [ do-something-2] x.gits.boot.system.service.AsyncService  : do something, message=index = 12020-04-19 23:42:42.488  INFO 21168 --- [ do-something-3] x.gits.boot.system.service.AsyncService  : do something, message=index = 2

由此可見已經(jīng)達(dá)到異步執(zhí)行的效果了，并且使用到了咱們配置的線程池。

獲取異步方法返回值

當(dāng)異步方法有返回值時(shí)，如何獲取異步方法執(zhí)行的返回結(jié)果呢？這時(shí)需要異步調(diào)用的方法帶有返回值CompletableFuture。

CompletableFuture是對(duì)Feature的增強(qiáng)，F(xiàn)eature只能處理簡單的異步任務(wù)，而CompletableFuture可以將多個(gè)異步任務(wù)進(jìn)行復(fù)雜的組合。如下：

@RestControllerpublic class AsyncController {    @Autowired    private AsyncService asyncService;    @SneakyThrows    @ApiOperation("異步 有返回值")    @GetMapping("/open/somethings")    public String somethings() {        CompletableFuture createOrder = asyncService.doSomething1("create order");        CompletableFuture reduceAccount = asyncService.doSomething2("reduce account");        CompletableFuture saveLog = asyncService.doSomething3("save log");        // 等待所有任務(wù)都執(zhí)行完        CompletableFuture.allOf(createOrder, reduceAccount, saveLog).join();        // 獲取每個(gè)任務(wù)的返回結(jié)果        String result = createOrder.get() + reduceAccount.get() + saveLog.get();        return result;    }}@Slf4j@Servicepublic class AsyncService {    @Async("doSomethingExecutor")    public CompletableFuture doSomething1(String message) throws InterruptedException {        log.info("do something1: {}", message);        Thread.sleep(1000);        return CompletableFuture.completedFuture("do something1: " + message);    }    @Async("doSomethingExecutor")    public CompletableFuture doSomething2(String message) throws InterruptedException {        log.info("do something2: {}", message);        Thread.sleep(1000);        return CompletableFuture.completedFuture("; do something2: " + message);    }    @Async("doSomethingExecutor")    public CompletableFuture doSomething3(String message) throws InterruptedException {        log.info("do something3: {}", message);        Thread.sleep(1000);        return CompletableFuture.completedFuture("; do something3: " + message);    }}

訪問接口

C:\Users\Administrator>curl -X GET "http://localhost:8200/open/somethings" -H "accept: */*"do something1: create order; do something2: reduce account; do something3: save log

控制臺(tái)上關(guān)鍵日志如下：

2020-04-20 00:27:42.238  INFO 5672 --- [ do-something-3] x.gits.boot.system.service.AsyncService  : do something3: save log2020-04-20 00:27:42.238  INFO 5672 --- [ do-something-2] x.gits.boot.system.service.AsyncService  : do something2: reduce account2020-04-20 00:27:42.238  INFO 5672 --- [ do-something-1] x.gits.boot.system.service.AsyncService  : do something1: create order

注意事項(xiàng)

@Async注解會(huì)在以下幾個(gè)場(chǎng)景失效，也就是說明明使用了@Async注解，但就沒有走多線程。

異步方法使用static關(guān)鍵詞修飾；異步類不是一個(gè)Spring容器的bean（一般使用注解@Component和@Service，并且能被Spring掃描到）；SpringBoot應(yīng)用中沒有添加@EnableAsync注解；在同一個(gè)類中，一個(gè)方法調(diào)用另外一個(gè)有@Async注解的方法，注解不會(huì)生效。原因是@Async注解的方法，是在代理類中執(zhí)行的。

通過上邊幾個(gè)示例，@Async實(shí)際還是通過Future或CompletableFuture來異步執(zhí)行的，Spring又封裝了一下，讓我們使用的更方便。

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