CompletionService 处理异步任务

案例:

public static void main(String[] args) throws Exception {ExecutorService executorService = Executors.newCachedThreadPool();ArrayList<Future<Integer>> list = new ArrayList<>();Future<Integer> future_15 = executorService.submit(() -> {TimeUnit.SECONDS.sleep(15);System.out.println("执行时长为15s的执行完成。");return 15;});list.add(future_15);Future<Integer> future_5 = executorService.submit(() -> {TimeUnit.SECONDS.sleep(5);System.out.println("执行时长为5s的执行完成。");return 5;});list.add(future_5);Future<Integer> future_10 = executorService.submit(() -> {TimeUnit.SECONDS.sleep(10);System.out.println("执行时长为10s的执行完成。");return 10;});list.add(future_10);System.out.println("开始准备获取结果");for (Future<Integer> future : list) {System.out.println("future.get() = " + future.get());}Thread.currentThread().join();}

上述代码输出结果：

可以看到耗时最长的最先获取结果，让耗时短的线程等着耗时长的线程

修改使用【ExecutorCompletionService】提交任务：

public static void main(String[] args) throws InterruptedException, ExecutionException {ExecutorService executorService = Executors.newCachedThreadPool();ExecutorCompletionService<Integer> completionService =new ExecutorCompletionService<>(executorService);completionService.submit(() -> {TimeUnit.SECONDS.sleep(15);System.out.println("执行时长为【15】的执行完成。");return 15;});completionService.submit(() -> {TimeUnit.SECONDS.sleep(5);System.out.println("执行时长为【5】的执行完成。");return 5;});completionService.submit(() -> {TimeUnit.SECONDS.sleep(10);System.out.println("执行时长为【10】的执行完成。");return 10;});System.out.println("开始准备获取结果");//循环3次是因为上面提交了3个异步任务for (int i = 0; i < 3; i++) {Integer returnStr = completionService.take().get();System.out.println("future.get() = " + returnStr);}Thread.currentThread().join();}

运行结果：