Callable 如何从预定义的 void 回调中返回值？

Question

我正在使用一个与数据相关的API接口，它有一个关键的void回调函数，它会自动调用来标记一些IO操作的结束。我想上课

Callable<String>

并使用

Future<String> result

。

我很难弄清楚如何让 Callable 返回一个字符串。制作一个

String returnResult(){return this.result}

函数在内部调用是行不通的。

请指教。

看起来像：

public class MyCallable implements someAPIWrapper, Callable<String> {
    
    String result;

    @Override
    public void endOfJobCallback() { //predefined API callback marking end of work
      /*
      usually read the data and write to a file, but not my case.
      how to return this.result string from here?
      */
    }

    @Override
    public String call() throws Exception {
      //some logic stuff
      //make API call to request a bunch of data
      //inside a loop to listen to incoming messages, receiving and appending to the *result* variable
      //end of all messages signalled by the ending callback, stop loop and return result var
    }

}

class Main {
    public static void main(String[] args){
      MyCallable callable = new MyCallable();
      ExecutorService executor = Executors.newFixedThreadPool(2);
      Future<String> future = executor.submit(callable);
      String result = future.get(); //blocking until result ready
    }
}

Answer 1

您可以使用（原子）布尔值来知道何时停止循环：

public class MyCallable implements someAPIWrapper, Callable<String> {
    
    String result;
    private final AtomicBoolean complete = new AtomicBoolean();

    @Override
    public void endOfJobCallback() { //predefined API callback marking end of work
      complete.set(true); //set Boolean to true atomically 
    }

    @Override
    public String call() throws Exception {
      while (!complete.get()) {
        //Do your stuff
      }
      //if you reach this the callback was called
      return result;
    }

}