Java实现异步调用

一、创建线程


@Test
public void test0() throws Exception {
 System.out.println("main函数开始执行");
 Thread thread=new Thread(new Runnable() {
   @Override
   public void run() {
     System.out.println("===task start===");
     try {
       Thread.sleep(5000);
     } catch (InterruptedException e) {
       e.printStackTrace();
     }
     System.out.println("===task finish===");
   }
 });

 thread.start();
 System.out.println("main函数执行结束");

}



二、Future

jdk8之前的实现方式,在JUC下增加了Future,从字面意思理解就是未来的意思,但使用起来却着实有点鸡肋,并不能实现真正意义上的异步,获取结果时需要阻塞线程,或者不断轮询。


@Test
public void test1() throws Exception {

   System.out.println("main函数开始执行");

   ExecutorService executor = Executors.newFixedThreadPool(1);
   Future<Integer> future = executor.submit(new Callable<Integer>() {
       @Override
       public Integer call() throws Exception {
           System.out.println("===task start===");
           Thread.sleep(5000);
           System.out.println("===task finish===");
           return 3;
       }
   });
   //这里需要返回值时会阻塞主线程,如果不需要返回值使用是OK的。倒也还能接收
   //Integer result=future.get();
   System.out.println("main函数执行结束");
   System.in.read();

}


三、CompletableFuture

使用原生的CompletableFuture实现异步操作,加上对lambda的支持,可以说实现异步任务已经发挥到了极致。


@Test
public void test2() throws Exception {
   System.out.println("main函数开始执行");
   ExecutorService executor = Executors.newFixedThreadPool(2);
   CompletableFuture<Integer> future = CompletableFuture.supplyAsync(new Supplier<Integer>() {
       @Override
       public Integer get() {
           System.out.println("===task start===");
           try {
               Thread.sleep(5000);
           } catch (InterruptedException e) {
               e.printStackTrace();
           }
           System.out.println("===task finish===");
           return 3;
       }
   }, executor);
   future.thenAccept(e -> System.out.println(e));
   System.out.println("main函数执行结束");
}


四、Spring的Async注解

使用spring实现异步需要开启注解,可以使用xml方式或者java config的方式。


xml方式: <task:annotation-driven />


<task:annotation-driven executor="executor" />
<task:executor id="executor"
       pool-size="2" 线程池的大小
       queue-capacity="100" 排队队列长度
       keep-alive="120" 线程保活时间(单位秒)
       rejection-policy="CALLER_RUNS" 对拒绝的任务处理策略 />


java方式:


@EnableAsync
public class MyConfig {

   @Bean
   public TaskExecutor executor(){
       ThreadPoolTaskExecutor executor=new ThreadPoolTaskExecutor();
       executor.setCorePoolSize(10); //核心线程数
       executor.setMaxPoolSize(20);  //最大线程数
       executor.setQueueCapacity(1000); //队列大小
       executor.setKeepAliveSeconds(300); //线程最大空闲时间
       executor.setThreadNamePrefix("fsx-Executor-"); //指定用于新创建的线程名称的前缀。
       executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
       return executor;
   }
}


(1)@Async


@Test
public void test3() throws Exception {
   System.out.println("main函数开始执行");
   myService.longtime();
   System.out.println("main函数执行结束");
}

@Async
public void longtime() {
   System.out.println("我在执行一项耗时任务");
   try {
       Thread.sleep(5000);
   } catch (InterruptedException e) {
       e.printStackTrace();
   }
   System.out.println("完成");

}


(2)AsyncResult

如果需要返回值,耗时方法返回值用AsyncResult包装。


@Test
public void test4() throws Exception {
   System.out.println("main函数开始执行");
   Future<Integer> future=myService.longtime2();
   System.out.println("main函数执行结束");
   System.out.println("异步执行结果:"+future.get());
}

@Async
public Future<Integer> longtime2() {
   System.out.println("我在执行一项耗时任务");

   try {
       Thread.sleep(8000);
   } catch (InterruptedException e) {
       e.printStackTrace();
   }

   System.out.println("完成");
   return new AsyncResult<>(3);
}



原文链接:https://www.cnblogs.com/sword-successful/p/11181714.html