本节我们一起学习一下SpringBoot中的异步调用，主要用于优化耗时较长的操作，提高系统性能和吞吐量。

一、新建项目，启动异步调用

首先给启动类增加注解@EnableAsync，支持异步调用

@EnableAsync
@SpringBootApplication
public class CathySpringbootDemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(CathySpringbootDemoApplication.class, args);
    }

}

然后定义要执行的Task，分类增加一个同步方法和异步方法，其中异步方法需要增加注解@Async

@Component
public class AsyncTask {
    /**
     * 异步任务，需要注解@Async
     *
     * @param taskId 任务编号id
     * @param second 执行时长，模拟慢任务
     * @return
     */
    @Async
    public Future<Boolean> asyncExec(int taskId, Long second) {
        exec(taskId, second);
        return new AsyncResult<>(Boolean.TRUE);
    }

    public void exec(int taskId, Long second) {
        System.out.println("开始执行任务" + taskId);
        try {
            Thread.sleep(second * 1000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        System.out.println("结束执行任务" + taskId);
    }
}

其实接下来就可以在controller中创建接口来进行简单的测试了

@RestController
@RequestMapping("/async")
public class AsyncController {
    @Autowired
    AsyncTask asyncTask;

    @GetMapping("sync_task")
    public String syncTask() {
        long start = System.currentTimeMillis();
        asyncTask.exec(1, 3L);
        asyncTask.exec(2, 3L);
        asyncTask.exec(3, 3L);
        long time = System.currentTimeMillis() - start;
        return "同步执行，耗时" + time;
    }

    @GetMapping("async_task")
    public String asyncTask() {
        long start = System.currentTimeMillis();
        Future<Boolean> f1 = asyncTask.asyncExec(1, 3L);
        Future<Boolean> f2 = asyncTask.asyncExec(2, 3L);
        Future<Boolean> f3 = asyncTask.asyncExec(3, 3L);
        try {
            f1.get();
            f2.get();
            f3.get();
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        } catch (ExecutionException e) {
            throw new RuntimeException(e);
        }

        long time = System.currentTimeMillis() - start;
        return "异步执行，耗时" + time;
    }
}

启动程序，查看接口响应结果：
http://localhost:16001/async/sync_task

http://localhost:16001/async/async_task

注意：异步方法和调用一定要写在不同的类中

二、线程池配置

上面的例子，在耗时服务多的情况下，使用异步方法确实提高了响应速度。但是它默认启用的是Spring默认的线程池SimpleAsyncTaskExecutor，不太灵活。我们把异步请求多增加几次调用看看效果：

@GetMapping("async_task")
    public String asyncTask() {
        long start = System.currentTimeMillis();
        List<Future<Boolean>> list = new ArrayList<>();
        for (int i = 0; i < 20; i++) {
            Future<Boolean> fi = asyncTask.asyncExec(i, 10L);
            list.add(fi);
        }
        for (int i = 0; i < 20; i++) {

            list.forEach(x -> {
                try {
                    x.get();
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                } catch (ExecutionException e) {
                    throw new RuntimeException(e);
                }
            });
        }

        long time = System.currentTimeMillis() - start;
        return "异步执行，耗时" + time;
    }

接下来，我们自定义线程池

@Bean
 public TaskExecutor threadPoolTaskExecutor(){
     ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
     executor.setCorePoolSize(8);
     executor.setMaxPoolSize(16);
     executor.setQueueCapacity(20);
     executor.setKeepAliveSeconds(30);
     executor.setWaitForTasksToCompleteOnShutdown(true);
     executor.setThreadNamePrefix("task-thread-");
     executor.setRejectedExecutionHandler(new ThreadPoolExecutor.DiscardOldestPolicy());

     executor.initialize();
     return executor;
 }

然后在异步方法的注解中，明确指定所使用的线程池

@Async("threadPoolTaskExecutor")
    public Future<Boolean> asyncExec(int taskId, Long second) {
        exec(taskId, second);
        return new AsyncResult<>(Boolean.TRUE);
    }

执行效果如下：

可以看出，线程池设置的参数已经生效。

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