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總的來說簡潔了FutureTask與線程池的配合使用

沒啥太大區別吧我覺得, 使用方法不一樣, 多了一些方法 ???

futureTask 創建異步任務

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

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

還有很多異步回調, 組合處理

創建任務

1. .supplyAsync

創建一個帶返回值的任務

2. .runAsync

創建一個不帶返回值的任務

      ExecutorService executorService = Executors.newFixedThreadPool(1);

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

以上兩個方法都有兩個構造方法, 默認不指定自定義線程池, 他會指定默認的提交任務的方法

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

  // 如果大于1核 則調用execute方法, 每次創建一個線程
  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(); }
  }

所以推薦自定義線程池的方式

異步回調

指的是異步任務結束后調用的任務

1. .thenApply

帶返回值的異步調用函數, 有入參, 有出參

2. .thenAccept

不帶返回值的異步回調函數, 有入參

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

      // future執行完之后執行的異步任務
      CompletableFuture<String> thenApply = future.thenApply((result) -> {
          System.out.println("future2　" +new Date());
          System.out.println(result);
          return "bbb" + result;
      });

3. .exceptionally

異步任務出現異常調用的回調方法

      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;
      });
      
      // 出現異常則返回異常, 沒異常則返回future的返回值
      System.out.println(exceptionally.get());

詳解Java CompletableFuture使用方法以及與FutureTask的區別

去掉異常

詳解Java CompletableFuture使用方法以及與FutureTask的區別

4. .whenComplete

當主任務出現異常時, 會終止任務,get的時候會拋出主任務的異常, 入參值為null, 否則正常運行

      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());

詳解Java CompletableFuture使用方法以及與FutureTask的區別