LeafCollector

Collector decouples the score from the collected doc: the score computation is skipped entirely if it's not needed. Collectors that do need the score should implement the {@link #setScorer} method, to hold onto the passed {@link Scorer} instance, and call {@link Scorer#score()} within the collect method to compute the current hit's score. If your collector may request the score for a single hit multiple times, you should use {@link ScoreCachingWrappingScorer}.

NOTE: The doc that is passed to the collect method is relative to the current reader. If your collector needs to resolve this to the docID space of the Multi*Reader, you must re-base it by recording the docBase from the most recent setNextReader call. Here's a simple example showing how to collect docIDs into a BitSet:

IndexSearcher searcher = new IndexSearcher(indexReader);
final BitSet bits = new BitSet(indexReader.maxDoc());
searcher.search(query, new Collector() {

public LeafCollector getLeafCollector(LeafReaderContext context)
       throws IOException {
     final int docBase = context.docBase;
     return new LeafCollector() {

      // ignore scorer
      public void setScorer(Scorer scorer) throws IOException {
      }

      public void collect(int doc) throws IOException {
        bits.set(docBase + doc);
      }

    };
}

});

Not all collectors will need to rebase the docID. For example, a collector that simply counts the total number of hits would skip it.

Inheritors