Spring@Async注解实现方法的异步调用

介绍

同步调用

先来演示一下什么是同步调用

@Component
public class Task {

    public void doTaskOne() throws InterruptedException {
        System.out.println("doTaskOne start " + System.currentTimeMillis());
        TimeUnit.SECONDS.sleep(1);
        System.out.println("doTaskOne end " + System.currentTimeMillis());
    }

    public void doTaskTwo() throws InterruptedException {
        System.out.println("doTaskTwo start " + System.currentTimeMillis());
        TimeUnit.SECONDS.sleep(1);
        System.out.println("doTaskTwo end " + System.currentTimeMillis()) ;
    }
}

测试方法

@RunWith(SpringRunner.class)
@SpringBootTest
public class TaskTest {

    @Autowired
    Task task;

    @Test
    public void doTask() throws InterruptedException {
        task.doTaskOne();
        task.doTaskTwo();
    }
}

输出如下

doTaskOne start 1566121320372
doTaskOne end 1566121321373
doTaskTwo start 1566121321373
doTaskTwo end 1566121322374

可以看到方法一执行完毕，方法二才会执行

异步调用不返回值

1.Spring Boot启动类上加@EnableAsync注解

@SpringBootApplication
@EnableAsync

2.方法上加@Async注解

@Component
public class Task {

    @Async
    public void doTaskOne() throws InterruptedException {
        System.out.println("doTaskOne start " + System.currentTimeMillis());
        TimeUnit.SECONDS.sleep(1);
        System.out.println("doTaskOne end " + System.currentTimeMillis());
    }

    @Async
    public void doTaskTwo() throws InterruptedException {
        System.out.println("doTaskTwo start " + System.currentTimeMillis());
        TimeUnit.SECONDS.sleep(1);
        System.out.println("doTaskTwo end " + System.currentTimeMillis()) ;
    }
}

测试类如下

@RunWith(SpringRunner.class)
@SpringBootTest
public class TaskTest {

    @Autowired
    Task task;

    @Test
    public void doTask() throws InterruptedException {
        task.doTaskOne();
        task.doTaskTwo();
        TimeUnit.SECONDS.sleep(3);
    }
}

最后的TimeUnit.SECONDS.sleep(3)保证主线程存活，不然主线程执行完看不到子线程输出的end，输出如下

doTaskOne start 1566121729140
doTaskTwo start 1566121729140
doTaskOne end 1566121730140
doTaskTwo end 1566121730140

看输出，2个任务同时启动。2个没有关系的任务以前需要2s才能执行完，异步后1s就能执行完，效率提高。

异步调用返回值

@Component
public class Task {

    @Async
    public Future<String> doTaskOne() throws InterruptedException {
        System.out.println("doTaskOne start " + System.currentTimeMillis());
        TimeUnit.SECONDS.sleep(1);
        System.out.println("doTaskOne end " + System.currentTimeMillis());
        return new AsyncResult<>("taskOne return");
    }

    @Async
    public Future<String> doTaskTwo() throws InterruptedException {
        System.out.println("doTaskTwo start " + System.currentTimeMillis());
        TimeUnit.SECONDS.sleep(1);
        System.out.println("doTaskTwo end " + System.currentTimeMillis());
        return new AsyncResult<>("taskTwo return");
    }
}

测试类

@RunWith(SpringRunner.class)
@SpringBootTest
public class TaskTest {

    @Autowired
    Task task;

    @Test
    public void doTask() throws InterruptedException, ExecutionException {
        Future<String> future1 = task.doTaskOne();
        Future<String> future2 = task.doTaskTwo();
        String result1 = future1.get();
        System.out.println(result1);
        String result2 = future2.get();
        System.out.println(result2);
    }
}

输出如下

doTaskTwo start 1566122170684
doTaskOne start 1566122170684
doTaskTwo end 1566122171684
doTaskOne end 1566122171684
taskOne return
taskTwo return

Future类的get方法是阻塞方法，没有结果返回时会一直阻塞。