On 6/6/10 10:48 AM, Alex Karasulu wrote:
On Sat, Jun 5, 2010 at 11:31 PM, Stefan Seelmann<[email protected]>wrote:
Emmanuel Lecharny schrieb:
On 6/5/10 12:18 PM, Felix Knecht wrote:
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On 06/05/10 12:02, Emmanuel Lecharny wrote:
On 6/5/10 11:57 AM, Felix Knecht wrote:
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The Cursor interface [1] throws almost for each method an
'Exception'. I
suggest to make this less generic and throw either the (from javadoc)
"UnsupportedOperationException" or in analogy to the Iterator a
"NoSuchElementException" for methods like before,after,last,first, ...
I saw that while I was propagating the LdapException through the
server.
IMO, we should define a base CursorException class, and derive some
more
specific exception like the one you suggest.
What would be the benefit of the Exception inflation instead of using
already existing ones where it logically makes sense?
The idea is to use the best Exception for each error case. If the
existing exceptions fit, then I think we can avoid defining our own tree
of exceptions. But I doubt we can cover all the cases with those
existing exception.
As I'm not a specialist of the Store code, maybe Alex or Stefan can
bring a bit more light on this aspect.
The org.apache.directory.shared.ldap.cursor package already defines
three exceptions, all extend "Exception":
- InvalidCursorPositionException
- InconsistentCursorStateException
- CursorClosedException
The InvalidCursorPositionException is thrown when calling Cursor.get()
but the cursor isn't positioned correctly. An option is to use a
NoSuchElementException instead.
The InconsistentCursorStateException is never used.
The CursorClosedException is thrown when Cursor.close() was called and
afterwards another cursor method is called. An option is to use an
IllegalStateException instead.
Other exceptions are thrown by the underlying data stores if there are
problems when getting data from an index table for example. I think most
of them are IOExceptions. Here it makes sense to define a custom
exception to wrap those guys.
The question is (and I think I can remember we already had such a
discussion): should we use checked or unchecked exceptions?
If we use checked exceptions it makes sense to define a base
CursorException and to derive the above mention exceptions from it.
If we use unchecked exceptions we should reuse the existing
IllegalStateException and NoSuchElementException.
I think this is a matter of how early we want to check/handle various issues
with a Cursors operation. If we want checks/handling to occur early where
the error occurs in the code using the Cursor then checked exceptions are
best. IMO I think this might be best.
On the other hand if it's OK to handle unchecked exceptions higher up in the
execution stack then let's go with unchecked. This however brings the need
to handle Cursor failures higher up outside of where the Cursor is used and
we loose some focus and possibly handle exceptions for the Cursor in regions
where it is less coherent.
+1 on checked exceptions.
+1 too.
/The Java Programming Language/, by Gosling, Arnold, and Holmes :
"Unchecked runtime exceptions represent conditions that, generally
speaking, reflect errors in your program's logic and cannot be
reasonably recovered from at run time."
--
Regards,
Cordialement,
Emmanuel Lécharny
www.nextury.com
