Dan Creswell wrote:
"ServiceClasspathSubItem is intended for client side filtering of lookup
* service results prior to clients using a service, the lookup service
* that implements this class, implements #getServiceItem(), so clients
* can obtain a complete ServiceItem when required after filtering."
I'm still wondering if it wouldn't be better for a client to send a list of
Entry's it's interested in seeing, separate from the set for matching to the
Registrar. The Registrar can then return ServiceItems for the matches and
pre-filter the Entry's per item. Especially given:
"Some fields in ServiceClasspathSubItem may be null, fields in Entry's may
* be null or even the service reference may be null, these fields would be
* non-null in a ServiceItem that resolves classes from dynamicly downloaded
* code or a remote codebase."
I think, if we do the filtering as I suggest, much of the comment re: nulls
above still applies in implementation but ultimately, the client will pick
Entry's for which it has the classpath such that it always deals in complete
Entry's and can have a level of predictability in respect of what is or is
not null. This might save clients having to do endless null checks etc that
can be a rich source of bugs and ugly code.
We might need the filter list to include specific subclasses as well....
Hmm, null is a problem, we could still have fields missing subclass
classes, which might prevent a subclass from unmarshalling.
Is there a way we can catch a class not found exception or similar and
still get the state of the superclass, or would this violate
polymorphism, method overrides etc?
I guess the likelihood of having null values is reduced, although not
eliminated.
If we compact the final array of Entry's so null entry's are removed,
the client only needs to find the Entry's it's interested in, likely
ignoring the others anyway.
So the client needs to ensure the Entry's are resolvable from the classpath.
I have thought about the case where a proxy uses the lookup service and
has Entry's in it's proxy classloader, but this could be subject to
security issues, where two services with different Subject's end up
sharing state.
We might also consider only including Entry's that don't have null field
values, this puts the impetus on the implementer to consider the Entry
field classes.
Cheers,
Peter.
