org.apache.lucene.search
Class FilteredDocIdSet

java.lang.Object
  org.apache.lucene.search.DocIdSet
      org.apache.lucene.search.FilteredDocIdSet

Direct Known Subclasses:

BitsFilteredDocIdSet

public abstract class FilteredDocIdSet
extends DocIdSet

Abstract decorator class for a DocIdSet implementation that provides on-demand filtering/validation mechanism on a given DocIdSet.

Technically, this same functionality could be achieved with ChainedFilter (under queries/), however the benefit of this class is it never materializes the full bitset for the filter. Instead, the match(int) method is invoked on-demand, per docID visited during searching. If you know few docIDs will be visited, and the logic behind match(int) is relatively costly, this may be a better way to filter than ChainedFilter.

See Also:

DocIdSet

Field Summary

Fields inherited from class org.apache.lucene.search.DocIdSet

EMPTY_DOCIDSET

Constructor Summary

FilteredDocIdSet(DocIdSet innerSet)
Constructor.

Method Summary

Bits	bits() Optionally provides a Bits interface for random access to matching documents.
boolean	isCacheable() This DocIdSet implementation is cacheable if the inner set is cacheable.
DocIdSetIterator	iterator() Implementation of the contract to build a DocIdSetIterator.
protected abstract boolean	match(int docid) Validation method to determine whether a docid should be in the result set.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

FilteredDocIdSet

public FilteredDocIdSet(DocIdSet innerSet)

Constructor.

Parameters:

innerSet - Underlying DocIdSet

Method Detail

isCacheable

public boolean isCacheable()

This DocIdSet implementation is cacheable if the inner set is cacheable.

Overrides:

isCacheable in class DocIdSet

bits

public Bits bits()
          throws IOException

Description copied from class: DocIdSet

Optionally provides a Bits interface for random access to matching documents.

Overrides:

bits in class DocIdSet

Returns:

null, if this DocIdSet does not support random access. In contrast to DocIdSet.iterator(), a return value of null does not imply that no documents match the filter! The default implementation does not provide random access, so you only need to implement this method if your DocIdSet can guarantee random access to every docid in O(1) time without external disk access (as Bits interface cannot throw IOException). This is generally true for bit sets like FixedBitSet, which return itself if they are used as DocIdSet.

Throws:

IOException

match

protected abstract boolean match(int docid)

Validation method to determine whether a docid should be in the result set.

Parameters:

docid - docid to be tested

Returns:

true if input docid should be in the result set, false otherwise.

iterator

public DocIdSetIterator iterator()
                          throws IOException

Implementation of the contract to build a DocIdSetIterator.

Specified by:

iterator in class DocIdSet

Throws:

IOException

See Also:

DocIdSetIterator, FilteredDocIdSetIterator