XOM API for Processing XML with Java

[Nils_Kilden-Pedersen AT Countrywide.Com]

xom-interest-bounces AT lists.ibiblio.org wrote on 11/25/2003 03:02:33 PM:

> Hmmm, I wonder if there's an inexpensive way I could test this on 
> getAttributevalue (and many similar calls) to warn the user what 
> they're doing wrong at least some of the time.

An attribute name cannot contain '/'. A URI doesn't have to contain this 
either, but mostly do.
>From elharo AT metalab.unc.edu  Tue Nov 25 18:54:13 2003
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Date: Tue, 25 Nov 2003 18:48:59 -0500
To: Nils_Kilden-Pedersen AT Countrywide.Com
From: Elliotte Rusty Harold <elharo AT metalab.unc.edu>
Subject: Should XOM check for illegal names passed to getter methods? (Was
        Re: [XOM-interest] Namespaces and attributes)
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At 3:18 PM -0800 11/25/03, Nils_Kilden-Pedersen AT Countrywide.Com wrote:
>xom-interest-bounces AT lists.ibiblio.org wrote on 11/25/2003 03:02:33 PM:
>
>>  Hmmm, I wonder if there's an inexpensive way I could test this on
>>  getAttributevalue (and many similar calls) to warn the user what
>>  they're doing wrong at least some of the time.
>
>An attribute name cannot contain '/'. A URI doesn't have to contain this
>either, but mostly do.

Yes. The question is whether I want to impose the cost of checking 
for that on every call to getAttribute() or getAttributeValue(). I 
suppose I could do this only after I've verified that no such 
attribute exists. This would mean the majority of the cases where you 
ask for the attribute and it exists would not pay the cost. It would 
still be a hit for some cases, but probably not too bad or too common.

I've just added code to provide a more explicit message for this case 
to the Verifier. Thus in the relevant attribute and element 
constructors a more explicit message is provided to help developers 
track down their mistakes. This does *not* change the behavior or API 
in any way aside from the exception message, and should have no 
performance cost in the non-exceptional case.

The question now is what to do when a getAttribute(Value) or 
getChildElement(s) call is about to return null (or an empty list for 
getChildElements). In that circumstance, I could easily call 
Verifier.checkName() on the name passed in. If the name is not a 
legal XML name this would throw an IllegalNameException, a runtime 
exception. Probably most of the time this is correct because passing 
an illegal name to a method is likely a programming error, unlike 
passing a bad name to a constructor. However, I have not been 
catching that up till now because it is not an error which would 
result in malformed document. Nonetheless catching it might make make 
XOM programs more robust.

What do people think? To me it feels like a good idea, but not an 
essential one.
-- 

   Elliotte Rusty Harold
   elharo AT metalab.unc.edu
   Effective XML (Addison-Wesley, 2003)
   http://www.cafeconleche.org/books/effectivexml
   http://www.amazon.com/exec/obidos/ISBN%3D0321150406/ref%3Dnosim/cafeaulaitA