Spring异步注解—@Async

被@Async标注的方法，称之为异步方法；这些方法将在执行的时候，将会在独立的线程中被执行，调用者无需等待它的完成，便可继续其余的操做。@Async也能够放在类上，表示整个类的全部方法都是异步的。@Async的惟一参数value的做用是：指定用该执行方法的执行器名称，执行器由咱们本身定义的,Executor或者TaskExecutor类型；该参数可为空。

基本用法示例代码：

在须要异步执行的方法加上@Async

@Component
public class SendMessge {

    /**
      * 异步发送消息方法
      */
    @Async
    public void send(int message){
        String currentThreadName = Thread.currentThread().getName();
        System.out.println(currentThreadName + ":" + message);
        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

而后在应用启动类上加上@EnableAsync

@SpringBootApplication
@EnableAsync
public class TestServerApplication {
    public static void main(String[] args) {
        SpringApplication.run(TestServerApplication.class, args);
    }
}

测试代码

@RunWith(SpringRunner.class)
@SpringBootTest
public class AsyncTest {
    @Autowired
    private SendMessge sendMessge;

    @Test
    public void sendTest() throws InterruptedException {
        for (int i = 0; i < 5; i++){
            sendMessge.send(i);
            System.out.println("send message: " +i);
        }
        Thread.sleep(1000);
    }
}

测试结果

send message: 0
send message: 1
send message: 2
send message: 3
send message: 4
SimpleAsyncTaskExecutor-2:1
SimpleAsyncTaskExecutor-5:4
SimpleAsyncTaskExecutor-3:2
SimpleAsyncTaskExecutor-1:0
SimpleAsyncTaskExecutor-4:3

咱们也能够自定义用于执行方法的执行器，这样咱们可以控制线程池大小，当咱们有多个异步方法时，就能够控制每一个方法的并发数量。

/**
 * 配置SendMessage的异步执行器
 */
@Configuration
@EnableAsync
public class ExecutorConfig {
    @Bean
    public Executor sendAsyncExecutor() {
        //spring的线程池执行器
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(10);
        executor.setMaxPoolSize(20);
        executor.setQueueCapacity(10);
        //线程名前缀
        executor.setThreadNamePrefix("sendMessage-Thread-");
        // 线程池无资源时拒绝新任务的处理策略，CallerRunsPolicy 表示由调用者所在的线程来执行
        executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
        executor.initialize();
        return executor;
    }
}

而后在咱们异步方法注解加上参数：@Async("sendAsyncExecutor")，这样就能够了。

上面的异步方法没有返回值，也不能处理异常，若是异步方法须要返回值和异常的处理就下面这样

@Component
public class SendMessge {

    /**
      * 异步发送消息方法
      */
    @Async("sendAsyncExecutor")
    public ListenableFuture send(String message) throws InterruptedException {
        String currentThreadName = Thread.currentThread().getName();
        Thread.sleep(500);
        if("error".equals(message)) {
            throw new RuntimeException("出错啦");
        }else{
            System.out.println(currentThreadName + ":" + message);
        }
        return new AsyncResult<>("send success: " + message);
    }
}

测试调用

@RunWith(SpringRunner.class)
@SpringBootTest
public class AsyncTest {
    @Autowired
    private SendMessge sendMessge;

    @Test
    public void sendTest() throws ExecutionException, InterruptedException {
        ListenableFuture result = sendMessge.send("error");
        result.addCallback((Object obj) -> { System.out.println(obj);},
                (Throwable ex) -> { System.out.println(ex);});
        Thread.sleep(1000);
    }
}

测试结果

//正常返回
sendMessage-Thread-1:Hi!
send success: Hi!

//异常返回
java.lang.RuntimeException: 出错啦