java - 如何在执行线程(如分页)时获取回调

Question

我正在使用线程和线程池。线程开始执行，在执行时，它将任务提交到线程池。线程从线程池中检索大量数据，所以我想要像分页概念这样的数据。我怎样才能实现它？

我已经实现了像下面的程序一样的回调。

public class TestAsync implements TaskCallBack {
    public static ExecutorService exService = Executors.newFixedThreadPool(5);
    public static void main(String args[]) throws InterruptedException, ExecutionException{
        Task t1 = new Task();
        t1.doTask(new TestAsync());

    }

    public static ExecutorService getPool(){
        return exService;
    }

    @Override
    public void taskCompleted(String obj) {
        System.out.println(obj);
    }
}

class Task {
 public void doTask(TaskCallBack tcb) throws InterruptedException, ExecutionException{
     FutureTask<String> ft = new FutureTask<>(new Task1());
     TestAsync.getPool().execute(ft);
     tcb.taskCompleted(ft.get());
 }

}

class Task1 implements Callable<String>{

    @Override
    public String call() throws Exception {
        System.out.println(Thread.currentThread().getName());   
        /*
               Here code for data retrieval

        */

        return "done";
    }

  interface TaskCallBack{
      public void taskCompleted(String obj);
  }

}

在上面的程序中，我正在等待整个执行。我不想那样。

Answer 1

您不应等待 get() 调用完成。如果这样做，您将阻塞调用者线程。

来自JavaDocs :

Waits if necessary for the computation to complete, and then retrieves its result.

相反，类似的东西可能对您有用:

class Task1 implements Callable<String> {
    private final TaskCallBack callback;

    // Pass the callback to the task
    public Task1(TaskCallBack callback) {
        this.callback = callback;
    }

    @Override
    public String call() throws Exception {
        System.out.println(Thread.currentThread().getName());
        /* Here code for data retrieval */

        // When the task has completed, return the result via the callback.
        // This will not be in the caller thread - it will instead be async
        callback.taskCompleted(result);

        return "done";
    }
}

并且，初始化它(并调用它):

FutureTask<String> ft = new FutureTask<>(new Task1(myCallback));
TestAsync.getPool().execute(ft);