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Lucene example source code file (FieldCacheTermsFilter.java)

This example Lucene source code file (FieldCacheTermsFilter.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

arrayindexoutofboundsexception, arrayindexoutofboundsexception, docidset, docidsetiterator, docidsetiterator, fieldcachetermsfilter, fieldcachetermsfilterdocidset, fieldcachetermsfilterdocidsetiterator, io, ioexception, no_more_docs, override, override, string, string

The Lucene FieldCacheTermsFilter.java source code

package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.util.OpenBitSet;
import org.apache.lucene.index.TermDocs;  // for javadocs

/**
 * A {@link Filter} that only accepts documents whose single
 * term value in the specified field is contained in the
 * provided set of allowed terms.
 * 
 * <p/>
 * 
 * This is the same functionality as TermsFilter (from
 * contrib/queries), except this filter requires that the
 * field contains only a single term for all documents.
 * Because of drastically different implementations, they
 * also have different performance characteristics, as
 * described below.
 * 
 * <p/>
 * 
 * The first invocation of this filter on a given field will
 * be slower, since a {@link FieldCache.StringIndex} must be
 * created.  Subsequent invocations using the same field
 * will re-use this cache.  However, as with all
 * functionality based on {@link FieldCache}, persistent RAM
 * is consumed to hold the cache, and is not freed until the
 * {@link IndexReader} is closed.  In contrast, TermsFilter
 * has no persistent RAM consumption.
 * 
 * 
 * <p/>
 * 
 * With each search, this filter translates the specified
 * set of Terms into a private {@link OpenBitSet} keyed by
 * term number per unique {@link IndexReader} (normally one
 * reader per segment).  Then, during matching, the term
 * number for each docID is retrieved from the cache and
 * then checked for inclusion using the {@link OpenBitSet}.
 * Since all testing is done using RAM resident data
 * structures, performance should be very fast, most likely
 * fast enough to not require further caching of the
 * DocIdSet for each possible combination of terms.
 * However, because docIDs are simply scanned linearly, an
 * index with a great many small documents may find this
 * linear scan too costly.
 * 
 * <p/>
 * 
 * In contrast, TermsFilter builds up an {@link OpenBitSet},
 * keyed by docID, every time it's created, by enumerating
 * through all matching docs using {@link TermDocs} to seek
 * and scan through each term's docID list.  While there is
 * no linear scan of all docIDs, besides the allocation of
 * the underlying array in the {@link OpenBitSet}, this
 * approach requires a number of "disk seeks" in proportion
 * to the number of terms, which can be exceptionally costly
 * when there are cache misses in the OS's IO cache.
 * 
 * <p/>
 * 
 * Generally, this filter will be slower on the first
 * invocation for a given field, but subsequent invocations,
 * even if you change the allowed set of Terms, should be
 * faster than TermsFilter, especially as the number of
 * Terms being matched increases.  If you are matching only
 * a very small number of terms, and those terms in turn
 * match a very small number of documents, TermsFilter may
 * perform faster.
 *
 * <p/>
 *
 * Which filter is best is very application dependent.
 */

public class FieldCacheTermsFilter extends Filter {
  private String field;
  private String[] terms;

  public FieldCacheTermsFilter(String field, String... terms) {
    this.field = field;
    this.terms = terms;
  }

  public FieldCache getFieldCache() {
    return FieldCache.DEFAULT;
  }

  @Override
  public DocIdSet getDocIdSet(IndexReader reader) throws IOException {
    return new FieldCacheTermsFilterDocIdSet(getFieldCache().getStringIndex(reader, field));
  }

  protected class FieldCacheTermsFilterDocIdSet extends DocIdSet {
    private FieldCache.StringIndex fcsi;

    private OpenBitSet openBitSet;

    public FieldCacheTermsFilterDocIdSet(FieldCache.StringIndex fcsi) {
      this.fcsi = fcsi;
      openBitSet = new OpenBitSet(this.fcsi.lookup.length);
      for (int i=0;i<terms.length;i++) {
        int termNumber = this.fcsi.binarySearchLookup(terms[i]);
        if (termNumber > 0) {
          openBitSet.fastSet(termNumber);
        }
      }
    }

    @Override
    public DocIdSetIterator iterator() {
      return new FieldCacheTermsFilterDocIdSetIterator();
    }

    /** This DocIdSet implementation is cacheable. */
    @Override
    public boolean isCacheable() {
      return true;
    }

    protected class FieldCacheTermsFilterDocIdSetIterator extends DocIdSetIterator {
      private int doc = -1;

      @Override
      public int docID() {
        return doc;
      }

      @Override
      public int nextDoc() {
        try {
          while (!openBitSet.fastGet(fcsi.order[++doc])) {}
        } catch (ArrayIndexOutOfBoundsException e) {
          doc = NO_MORE_DOCS;
        }
        return doc;
      }

      @Override
      public int advance(int target) {
        try {
          doc = target;
          while (!openBitSet.fastGet(fcsi.order[doc])) {
            doc++;
          }
        } catch (ArrayIndexOutOfBoundsException e) {
          doc = NO_MORE_DOCS;
        }
        return doc;
      }
    }
  }
}

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