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詳解在SpringBoot如何優(yōu)雅的使用多線程

更新時間：2023年02月07日 16:11:00 作者：?????

這篇文章主要帶大家快速了解一下@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注解失效的幾個坑，感興趣的小伙伴可以了解一下

在 SpringBoot 應(yīng)用中，經(jīng)常會遇到在一個接口中，同時做事情1，事情2，事情3，如果同步執(zhí)行的話，則本次接口時間取決于事情1 2 3執(zhí)行時間之和；如果三件事同時執(zhí)行，則本次接口時間取決于事情1 2 3執(zhí)行時間最長的那個，合理使用多線程，可以大大縮短接口時間。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.

快速使用

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

@Configuration
@EnableAsync
public class AsyncConfiguration {
 
    @Bean("doSomethingExecutor")
    public Executor doSomethingExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        // 核心線程數(shù)：線程池創(chuàng)建時候初始化的線程數(shù)
        executor.setCorePoolSize(10);
        // 最大線程數(shù)：線程池最大的線程數(shù)，只有在緩沖隊列滿了之后才會申請超過核心線程數(shù)的線程
        executor.setMaxPoolSize(20);
        // 緩沖隊列：用來緩沖執(zhí)行任務(wù)的隊列
        executor.setQueueCapacity(500);
        // 允許線程的空閑時間60秒：當(dāng)超過了核心線程之外的線程在空閑時間到達(dá)之后會被銷毀
        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

@RestController
public 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);
        }
        return "success";
    }
}
 
 
@Slf4j
@Service
public 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

2023-02-06 23:42:42.486 INFO 21168 --- [io-8200-exec-17] x.g.b.system.controller.AsyncController : do something end, time 8 milliseconds
2023-02-06 23:42:42.488 INFO 21168 --- [ do-something-1] x.gits.boot.system.service.AsyncService : do something, message=index = 0
2023-02-06 23:42:42.488 INFO 21168 --- [ do-something-5] x.gits.boot.system.service.AsyncService : do something, message=index = 4
2023-02-06 23:42:42.488 INFO 21168 --- [ do-something-4] x.gits.boot.system.service.AsyncService : do something, message=index = 3
2023-02-06 23:42:42.488 INFO 21168 --- [ do-something-6] x.gits.boot.system.service.AsyncService : do something, message=index = 5
2023-02-06 23:42:42.488 INFO 21168 --- [ do-something-9] x.gits.boot.system.service.AsyncService : do something, message=index = 8
2023-02-06 23:42:42.488 INFO 21168 --- [ do-something-8] x.gits.boot.system.service.AsyncService : do something, message=index = 7
2023-02-06 23:42:42.488 INFO 21168 --- [do-something-10] x.gits.boot.system.service.AsyncService : do something, message=index = 9
2023-02-06 23:42:42.488 INFO 21168 --- [ do-something-7] x.gits.boot.system.service.AsyncService : do something, message=index = 6
2023-02-06 23:42:42.488 INFO 21168 --- [ do-something-2] x.gits.boot.system.service.AsyncService : do something, message=index = 1
2023-02-06 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，如何獲取異步方法執(zhí)行的返回結(jié)果呢？這時需要異步調(diào)用的方法帶有返回值CompletableFuture。

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

@RestController
public class AsyncController {
 
    @Autowired
    private AsyncService asyncService;
 
    @SneakyThrows
    @ApiOperation("異步 有返回值")
    @GetMapping("/open/somethings")
    public String somethings() {
        CompletableFuture<String> createOrder = asyncService.doSomething1("create order");
        CompletableFuture<String> reduceAccount = asyncService.doSomething2("reduce account");
        CompletableFuture<String> saveLog = asyncService.doSomething3("save log");
 
        // 等待所有任務(wù)都執(zhí)行完
        CompletableFuture.allOf(createOrder, reduceAccount, saveLog).join();
        // 獲取每個任務(wù)的返回結(jié)果
        String result = createOrder.get() + reduceAccount.get() + saveLog.get();
        return result;
    }
}
 
 
@Slf4j
@Service
public class AsyncService {
 
    @Async("doSomethingExecutor")
    public CompletableFuture<String> doSomething1(String message) throws InterruptedException {
        log.info("do something1: {}", message);
        Thread.sleep(1000);
        return CompletableFuture.completedFuture("do something1: " + message);
    }
 
    @Async("doSomethingExecutor")
    public CompletableFuture<String> doSomething2(String message) throws InterruptedException {
        log.info("do something2: {}", message);
        Thread.sleep(1000);
        return CompletableFuture.completedFuture("; do something2: " + message);
    }
 
    @Async("doSomethingExecutor")
    public CompletableFuture<String> 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:8080/open/something" -H "accept: */*"
do something1: create order;
do something2: reduce account;
do something3: save log

控制臺上關(guān)鍵日志如下：

2023-02-06 00:27:42.238 INFO 5672 --- [ do-something-3] x.gits.boot.system.service.AsyncService : do something3: save log
2023-02-06 00:27:42.238 INFO 5672 --- [ do-something-2] x.gits.boot.system.service.AsyncService : do something2: reduce account
2023-02-06 00:27:42.238 INFO 5672 --- [ do-something-1] x.gits.boot.system.service.AsyncService : do something1: create order