Re: [aspectj-users] Need help refactoring an input validation aspect

[David Coppit <aspectj@xxxxxxxxxx>]

On Mon, 16 May 2005, David Coppit wrote:

> I'm just getting started with AspectJ, and have gotten stuck on
> extracting some exception handling concerns. Can anyone point me in the
> right direction?

Harold Ossher reminded me that around advice can work in this situation.
(Thanks!) Here's the solution for posterity.

Here's the original code:

  private static int promptForNumber(final BufferedReader stdin) {
    int inputSize = 0;

    boolean inputIsValid = false;
    while (!inputIsValid) {
      try {
        inputSize = Integer.parseInt(stdin.readLine());

        inputIsValid = true;
      } catch (IOException e) {
        System.err.println(
          "Encountered an I/O exception. Exiting.");
        System.exit(1);
      } catch (NumberFormatException e) {
        System.err.println(
          "Invalid number entered. (" + e.getMessage() + ")" );
      }
    }

    return inputSize;
  }

Here's the AspectJ code:

  // Yay! A single, simple call
  private static int promptForNumber(final BufferedReader stdin) {
    return Integer.parseInt(stdin.readLine());
  }

  aspect IOExceptionHandling {
    // Let the exception come out of the method so we can more easily catch it
    // with an around advice.
    declare soft : IOException : call(String BufferedReader.readLine());

    pointcut promptForNumber(): call(String BufferedReader.readLine());

    String around(): promptForNumber() {
      String value = "";

      try {
        value = proceed();
      } catch (org.aspectj.lang.SoftException e) {
        if (e.getWrappedThrowable() instanceof IOException) {
          System.err.println("Encountered an I/O exception. Exiting.");
          System.exit(1);
        }
        else
          // Can this happen?
          throw e;
      }

      return value;
    }

  }

  aspect InputValidation {

    pointcut promptForNumber(BufferedReader stdin):
        call(int Average.promptForNumber(BufferedReader)) && args(stdin);

    // promptForNumber is called by both readData and promptForValues, so
    // only do this check for the former.
    after() returning(int inputSize): promptForNumber(BufferedReader) &&
        !cflow( call(Vector Average.promptForValues(BufferedReader,int)) ) &&
        cflow( call(Vector Average.readData()) ) {
      if (inputSize <= 0)
        throw new NumberFormatException( "The number must be greater than 0.");
    }

    // This advice must follow the previous for precedence to be correct
    // and the thrown exception caught by this advice's exception handler.
    int around(BufferedReader stdin): promptForNumber(BufferedReader) &&
        args(stdin) {
      int value = 0;

      boolean inputIsValid = false;
      while (!inputIsValid) {
        try {
          value = proceed(stdin);

          inputIsValid = true;
        } catch (NumberFormatException e) {
          System.err.println(
            "Invalid number entered. (" + e.getMessage() + ")" );
        }
      }

      return value;
    }

  }

David