Exception Handling Standards -The exception Exception should never been thrown. Always Subclass Exception and throw the subclassed Classes.

Question

In the current project my exception handling implementation is as follows :
Exception Handling Layer wise :
DL layer :
catch (Exception ex)
bool rethrow = ExceptionPolicy.HandleException(ex, "Ui Policy");
if (rethrow)
throw;
BL Layer
catch (Exception ex)
bool rethrow = ExceptionPolicy.HandleException(ex, "Ui Policy");
if (rethrow)
throw;
UI Layer
catch (Exception ex)
bool rethrow = ExceptionPolicy.HandleException(ex, "Ui Policy");
if (rethrow)
Response.Redirect("ErrorPage.aspx", false);
We have a tool to check the standards. And tool output is as follows :
The exception Exception should never been thrown. Always Subclass Exception and throw the subclassed Classes.
I need suggestions on how to implement the same according to standards.

Answer 1

Your tool is wrong if it says to never throw Exception.  This was a common recommendation back in the .NET v1 days but has long since been thrown out.  It is perfectly fine to use Exception when you have a general exception that provides no information
that an application can use to make an informed opinion.
The general rules of exception throwing is to throw the most specific exception that makes sense. If there is no specific exception that applies and it would be useful for the caller to handle the exception differently than other exceptions then creating
a custom exception type is warranted.  Otherwise throwing Exception is reasonable. As an example you might have an application that pulls back product data given an ID. There is no built in exception that says the ID is invalid. However an invalid ID
is something that an application may want to handle differently than, say, an exception about the product being discontinued.  Therefore it might make sense to create an ItemNotFoundException exception that the application can react to.
Conversely there is no benefit in having different exception types for disk full and disk quota met. The application will respond the same in either case.
Michael Taylor
http://blogs.msmvps.com/p3net