Question

假设我有一个类定义要完成的大块工作，可以生成多个已检查的异常。

class WorkerClass{
   public Output work(Input input) throws InvalidInputException, MiscalculationException {
      ...
   }
}

现在假设我有一个可以调用这个类的GUI。我使用SwingWorker委派任务。

Final Input input = getInput();
SwingWorker<Output, Void> worker = new SwingWorker<Output, Void>() {
        @Override
        protected Output doInBackground() throws Exception {
            return new WorkerClass().work(input);
        }
};

如何处理从SwingWorker抛出的可能异常？我想区分我的worker类的异常（InvalidInputException和MiscalculationException），但ExecutionException包装器使事情变得复杂。我只想处理这些异常 - 不应该捕获OutOfMemoryError。

try{
   worker.execute();
   worker.get();
} catch(InterruptedException e){
   //Not relevant
} catch(ExecutionException e){
   try{
      throw e.getCause(); //is a Throwable!
   } catch(InvalidInputException e){
      //error handling 1
   } catch(MiscalculationException e){
      //error handling 2
   }
}
//Problem: Since a Throwable is thrown, the compiler demands a corresponding catch clause.

Answer 1

catch (ExecutionException e) {
    Throwable ee = e.getCause ();

    if (ee instanceof InvalidInputException)
    {
        //error handling 1
    } else if (ee instanceof MiscalculationException e)
    {
        //error handling 2
    }
    else throw e; // Not ee here
}

Answer 2

您可以使用ugly (smart?) hack将throwable转换为未经检查的异常。优点是调用代码将接收工作线程抛出的任何异常，无论是选中还是未选中，但您不必更改方法的签名。

try {
    future.get();
} catch (InterruptedException ex) {
} catch (ExecutionException ex) {
    if (ex.getCause() instanceof InvalidInputException) {
        //do your stuff
    } else {
        UncheckedThrower.throwUnchecked(ex.getCause());
    }
}

将UncheckedThrower定义为：

class UncheckedThrower {

    public static <R> R throwUnchecked(Throwable t) {
        return UncheckedThrower.<RuntimeException, R>trhow0(t);
    }

    @SuppressWarnings("unchecked")
    private static <E extends Throwable, R> R trhow0(Throwable t) throws E {
        throw (E) t;
    }
}

Answer 3

尝试/多捕获：

try {
    worker.execute();
    worker.get();
} catch (InterruptedException e) {
    //Not relevant
} catch (InvalidInputException e) {
    //stuff
} catch (MiscalculationException e) {
    //stuff
}

或使用ExecutionException包装器：

catch (ExecutionException e) {
    e = e.getCause();
    if (e.getClass() == InvalidInputException.class) {
        //stuff
    } else if (e.getClass() == MiscalculationException.class) {
        //stuff
    }
}

或者，如果您希望将异常的子类视为父母：

catch (ExecutionException e) {
    e = e.getCause();
    if (e instanceof InvalidInputException) {
        //stuff
    } else if (e instanceof MiscalculationException) {
        //stuff
    }
}

处理ExecutionException的原因

3 个答案: