Less roundabout keySet filter for keys

Question

Hi,
I'm attempting to use a filter to query keys in a partitioned cache that match a certain class type. keySet() by default appears to return to the filter the values of the entry. The same appears true of entrySet() as well. I want my filter to evaluate the keys in the cache, and for those keys that meet the criteria, return the keys.
After some poking around, I was able to do this via the following, which seems very roundabout. It seems like this should be a very common operation, and I'm surprised there doesn't seem to be a more direct way to do this. Is there an easier way to do this?
static public class KeyFilter extends ExtractorFilter
public KeyFilter( ValueExtractor i_ext, Filter i_filter )
super( i_ext );
m_filter = i_filter;
protected boolean evaluateExtracted( Object i_obj )
return m_filter.evaluate( i_obj );
private Filter m_filter;
and use it like this:
ClassFilter filter = new ClassFilter( MyKeyClass.class );
Set< MyKeyClass > set = (Set< MyKeyClass >)
db.keySet( new KeyFilter( new KeyExtractor( NullImplementation.NullValueExtractor.INSTANCE ), filter ) );

Answer 1

Hi,
there are other approaches which you can take:
1. Coherence provides an out-of-the-box KeyExtractor, which takes another extractor for further chaining. This allows you to extract something from the key instead of the value. You can just write
cache.keySet(new KeyExtractor(IdentityExtractor.INSTANCE), filter);to achieve what you wanted, you don't need to write that KeyFilter class of your own, if you want to examine the entire key.
If the filter is a ParallelAwareFilter implementor, then you can filter in parallel in the caches.
2. For more complex things, you can implement your own EntryExtractor and EntryFilter descendants/implementors.
Best regards,
Robert
Edited by: robvarga on Jan 20, 2009 8:00 PM
Example erroneous. Look below.