Exception cast in Java

[Manikandan Swaminathan]

In a simple web application(No Struts or Spring), lets say i am getting an exception in the business layer and i want that to be sent to the UI layer for some reasons.
How can this be acheived? I have heard something like exception cast in Java. I googled for this,but i was not able to get the required informaton.
Can anyone please let me know the details?

Cheers

[Matthew Brown]

I'm not sure what you mean by exception cast. The easiest way to get an exception from the business layer to the UI is just to throw it (or not catch it) - it will bubble up until you handle it, and if you only handle it in the UI that's where it will end up.

One thing that's quite common (and that might be what you're looking for) is when you want the business layer to throw a particular special type of exception so the UI doesn't have to know about the internal workings. Then you can catch a general exception, wrap it in your special one, and throw that. The pattern looks something like this:

public class BusinessException extends Exception {
    public BusinessException(Exception e) {
        super(e);
    }
    // typically you'd have three other constructors, but this is the only one I need in this demo
}

// Then in business interface:
public void doSomethingBusinessy(....) {
    try {
        ...
    }
    catch (Exception e) {
        throw new BusinessException(e);
    }
}