處理ExecutionException的原因

Question

假設我有一個類定義了要完成的大塊工作，可以產生多個檢查的異常。

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

現在假設我有一種可以調用這個類的GUI。我使用SwingWorker來委派任務。

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

如何處理SwingWorker引發的可能異常？我想區分工人類的異常（InvalidInputException和MiscalculationException），但是ExecutionException包裝會使事情複雜化。我只想處理這些異常 - 不應該發現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

嘗試/多陷阱：

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

或者與ExecutionException包裝：

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

或者，如果你希望得到的例外子像他們的父母：

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

Answer 3

您可以使用ugly (smart?) hack將throwable轉換爲未經檢查的異常。優點是調用代碼將接收工作線程拋出的任何異常，無論是選中還是未選中，但不必更改方法的簽名。

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

隨着UncheckedThrower定義爲：？什麼是處理爲ExecutionException的最佳方式]的

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; 
    } 
}