详解Java CompletableFuture使用方法以及与FutureTask的区别

总的来说简洁了FutureTask与线程池的配合使用

没啥太大区别吧我觉得, 使用方法不一样, 多了一些方法 ???

futureTask 创建异步任务

      FutureTask<String> stringFutureTask = new FutureTask<>(() -> {
          return "aa";
      });
      executorService.execute(stringFutureTask);
      System.out.println(stringFutureTask.get());

      CompletableFuture<String> future1 = CompletableFuture.supplyAsync(() -> {
          return "aa";
      }, executorService); // 不用手动提交了
      System.out.println(future1.get());

还有很多异步回调, 组合处理

创建任务

1. .supplyAsync

创建一个带返回值的任务

2. .runAsync

创建一个不带返回值的任务

      ExecutorService executorService = Executors.newFixedThreadPool(1);

      // 带返回值
      CompletableFuture future = CompletableFuture.supplyAsync(() -> {
          try {
              System.out.println("future　" + new Date());
              Thread.sleep(2000);
          } catch (InterruptedException e) {
              e.printStackTrace();
          }
          return "aaa";
      }, executorService); // 推荐使用

以上两个方法都有两个构造方法, 默认不指定自定义线程池, 他会指定默认的提交任务的方法

  // 查看cpu的核数是否大于1核
  private static final boolean useCommonPool =
      (ForkJoinPool.getCommonPoolParallelism() > 1);

  // 如果大于1核 则调用execute方法, 每次创建一个线程
  private static final Executor asyncPool = useCommonPool ?
      ForkJoinPool.commonPool() : new ThreadPerTaskExecutor();

  static final class ThreadPerTaskExecutor implements Executor {
      public void execute(Runnable r) { new Thread(r).start(); }
  }

所以推荐自定义线程池的方式

异步回调

指的是异步任务结束后调用的任务

1. .thenApply

带返回值的异步调用函数, 有入参, 有出参

2. .thenAccept

不带返回值的异步回调函数, 有入参

      CompletableFuture future = CompletableFuture.supplyAsync(() -> {
          try {
              System.out.println("future　" + new Date());
              Thread.sleep(2000);
          } catch (InterruptedException e) {
              e.printStackTrace();
          }
          return "aaa";
      }, executorService);

      // future执行完之后执行的异步任务
      CompletableFuture<String> thenApply = future.thenApply((result) -> {
          System.out.println("future2　" +new Date());
          System.out.println(result);
          return "bbb" + result;
      });

3. .exceptionally

异步任务出现异常调用的回调方法

      CompletableFuture future = CompletableFuture.supplyAsync(() -> {
          try {
              System.out.println("future　" + new Date());
              Thread.sleep(2000);
              int a = 1 / 0;
          } catch (InterruptedException e) {
              e.printStackTrace();
          }
          return "aaa";
      }, executorService);

      CompletableFuture<String> exceptionally = future.exceptionally((result) -> {
          System.out.println("future3 " + result);
          return "bbb" + result;
      });
      
      // 出现异常则返回异常, 没异常则返回future的返回值
      System.out.println(exceptionally.get());

详解Java CompletableFuture使用方法以及与FutureTask的区别

去掉异常

详解Java CompletableFuture使用方法以及与FutureTask的区别

4. .whenComplete

当主任务出现异常时, 会终止任务,get的时候会抛出主任务的异常, 入参值为null, 否则正常运行

      CompletableFuture future = CompletableFuture.supplyAsync(() -> {
          try {
              System.out.println("future　" + new Date());
              Thread.sleep(2000);
              int a = 1/0;
          } catch (InterruptedException e) {
              e.printStackTrace();
          }
          return "aaa";
      }, executorService);

      CompletableFuture<String> exceptionally = future.whenComplete((result, error) -> {
          System.out.println("future3 " + result);
          System.out.println("future3 " + error);
      });
      System.out.println(exceptionally.get());

详解Java CompletableFuture使用方法以及与FutureTask的区别