Async&Retryable简单介绍

问题1：Async在同一个类中注解失效，看如下代码

@SpringBootTest
@EnableAsync
public class ApplicationTest{
    @Test
    public void asyncTest(){
        async2();
        async1();
    }
    @Async
    public void async1(){
        System.out.println("say async1");
        System.out.println("say async1 end");
    }
    @Async
    public void async1(){
        System.out.println("say async2");
        try{
        Thread.sleep(5000l);//暂停5秒
        }catch(Exception e){
        }
        System.out.println("say async2 end");
    }
}

运行代码后输入如下结果：
say async2
say async2 end
say async1
say async1 end

结果跟我们预期的不符，为什么呢？
原来Spring扫描注解后，会创建一个如下代理类(伪代码)

class proxy$ApplicationTest{
ApplicationTest aT = new ApplicationTest();
public void asyncTest(){
//由于asyncTest()没有异步注解，所以不会异步执行，而是直接调用ApplicationTest实例的asyncTest()方法
aT.asyncTest();
}
public void async1(){
//异步执行
aT.async1();
}
public void async2(){
//异步执行
aT.async2();
}
}

举一反三，@cacheable,@Scheduled以及@Transactional 是否也是相同原因
问题2 异步线程没执行完就停止了，请看如下代码：

@SpringBootTest
@EnableAsync
public class ApplicationTest{
@Autowired
private AsyncTest asyncTest;
@Test
public void asyncTest2() throws InterruptedException{
asyncTest.async1();
asyncTest.async2();
System.out.println("结束了");
}
}
@Service
public class AsyncTest {
    @Async
    public void async1(){
        System.out.println("say async1");
        System.out.println("say async1 end");
    }

    @Async
    public void async2(){
        System.out.println("say async2");
        try{
            Thread.sleep(1000l);
        }catch (Exception e){
    System.out.println("------sleep 1000-------");
        }
        System.out.println("say async2 end");
    }
}

执行结果如下：
结束了
say async1
say async1 end
say async2

结果跟我们预期的不符，为什么呢？
其实junit是将test作为参数传递给了TestRunner的main函数。并通过main函数进行执行

public static void main(String[] args) {
        TestRunner aTestRunner = new TestRunner();

        try {
            TestResult r = aTestRunner.start(args);
            if (!r.wasSuccessful()) {
                System.exit(1);
            }

            System.exit(0);
        } catch (Exception var3) {
            System.err.println(var3.getMessage());
            System.exit(2);
        }

    }

在这里我们明显可以看到：当aTestRunner调用start方法后不会去等待子线程执行完毕在关闭主线程，
而是直接调用TestResult.wasSuccessful（）方法，
不管返回true or false 都会结束当前运行的jvm虚拟机，所以使用junit测试多线程方法的结果异常就正常了；

解决方案如下：

/**
     * 解决方案1
     * 延长主线程执行时间
     */
    @Test
    public void asyncTest3() throws InterruptedException {
        asyncServiceTest.async1();
        asyncServiceTest.async2();
        Thread.sleep(6000L);
        System.out.println("异步threadId:" + Thread.currentThread().getId());
        System.out.println("执行完毕!");
    }

/**
     * 解决方案2
     * 等待异步线程执行完后再继续后续逻辑
     */
    @Test
    public void asyncTest() throws InterruptedException, ExecutionException {
        Future task1 = asyncServiceTest.doTask1();
        Future task2 = asyncServiceTest.doTask2();

        while (true) {
            if (task1.isDone() && task2.isDone()) {
                System.out.println("Task1 result:" + task1.get());
                System.out.println("Task2 result:" + task2.get());
                break;
            }
            Thread.sleep(1000);
        }

        System.out.println("All tasks finished.");
    }

@Service
public class AsyncServiceTest {
    @Async
    public Future doTask1() throws InterruptedException {
        log.info("Task1 started.");
        long start = System.currentTimeMillis();
        Thread.sleep(5000);
        long end = System.currentTimeMillis();

        log.info("Task1 finished, time elapsed: {} ms.", end - start);

        return new AsyncResult<>("Task1 accomplished!");
    }

    @Async
    public Future doTask2() throws InterruptedException {
        log.info("Task2 started.");
        long start = System.currentTimeMillis();
        Thread.sleep(3000);
        long end = System.currentTimeMillis();

        log.info("Task2 finished, time elapsed: {} ms.", end - start);

        return new AsyncResult<>("Task2 accomplished!");
    }
    }

重试简单实现（retry）

@SpringBootTest
@EnableRetry
public class ApplicationTest3 {
    @Autowired
    private RetryServiceTest retryServiceTest;

    @Test
    public void retryTest3() {
        System.out.println("--start test retry---");
        retryServiceTest.retryTest3();
        System.out.println("--end test retry---");
    }
}

    @Retryable(value = {Exception.class}, maxAttempts = 5, backoff = @Backoff(delay = 1000, multiplier = 1))
    public void retryTest3() {
        String method = "retryTest3";
        log.info("[{}]do something...", method);
        throw new RemoteAccessException("RemoteAccessException....");
    }

--start test retry---
2018-04-17 10:02:05.706  INFO 7952 --- [           main] c.t.retry.servicetest.RetryServiceTest   : [retryTest3]do something...
2018-04-17 10:02:06.708  INFO 7952 --- [           main] c.t.retry.servicetest.RetryServiceTest   : [retryTest3]do something...
2018-04-17 10:02:07.709  INFO 7952 --- [           main] c.t.retry.servicetest.RetryServiceTest   : [retryTest3]do something...
2018-04-17 10:02:08.709  INFO 7952 --- [           main] c.t.retry.servicetest.RetryServiceTest   : [retryTest3]do something...
2018-04-17 10:02:09.709  INFO 7952 --- [           main] c.t.retry.servicetest.RetryServiceTest   : [retryTest3]do something...
RemoteAccessException....
recover....
--end test retry---

异步注解跟重试注解组合使用

@SpringBootTest
@EnableRetry
@RunWith(SpringRunner.class)
@EnableAsync
@Slf4j
public class ApplicationTest4 {
    @Autowired
    private RetryServiceTest retryServiceTest;

    @Test
    public void retryTest() {
        log.info("-----start retryTest------");
        Future task = retryServiceTest.retryTest();
        while (true) {
            if (task.isDone()) {
                log.info("---finish----");
                break;
            }
        }


    }
}
@Service
@Slf4j
public class RetryServiceTest {
@Async
    @Retryable(value = {Exception.class}, maxAttempts = 5, backoff = @Backoff(delay = 1000, multiplier = 1))
    public Future retryTest() {
        String method = "retryTest";
        log.info("[{}]do something...", method);
        throw new RemoteAccessException("RemoteAccessException....");
    }
    @Recover
    public void recover(Exception e) {
        System.out.println(e.getMessage());
        System.out.println("recover....");
    }
    }

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