BigramSpanRangeQuery.java

package org.apache.lucene.bigram;


/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed 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.util.Set;
import org.apache.lucene.index.Term;
import org.apache.lucene.search.spans.SpanRangeQuery;

/**
 * Matches spans containing terms within a specified range. Performs extra
 * filtering to make sure bi-grams are not matched.
 */
public class BigramSpanRangeQuery extends SpanRangeQuery 
{
  private Set stopSet;

  /** Constructs a span query selecting all terms greater than
   * <code>lowerTerm</code> but less than <code>upperTerm</code>.
   * There must be at least one term and either term may be null,
   * in which case there is no bound on that side, but if there are
   * two terms, both terms <b>must</b> be for the same field. Applies
   * a limit on the total number of terms matched.
   */
  public BigramSpanRangeQuery(Term lowerTerm, Term upperTerm,
                              boolean inclusive, int termLimit) 
  {
    super(lowerTerm, upperTerm, inclusive, termLimit);
  }

  public void setStopWords(Set set) {
    this.stopSet = set;
  }

  protected boolean shouldSkipTerm(Term term) 
  {
    if (stopSet == null)
      return false;

    // Skip stop words
    if (stopSet.contains(term.text()))
      return true;

    // Skip bi-grams containing stop words. 
    if (BigramQueryRewriter.isBigram(stopSet, term.text()))
      return true;

    // Others are okay.
    return false;
  }
} // class BigramSpanRangeQuery