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Lucene example source code file (MultiTermQuery.java)

This example Lucene source code file (MultiTermQuery.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

booleanquery, constant_score_auto_rewrite_default, io, ioexception, multitermquery, multitermquery, object, override, override, query, query, rewritemethod, rewritemethod, termquery, toptermsboostonlybooleanqueryrewrite

The Lucene MultiTermQuery.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 java.io.Serializable;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;

import org.apache.lucene.queryParser.QueryParser; // for javadoc

/**
 * An abstract {@link Query} that matches documents
 * containing a subset of terms provided by a {@link
 * FilteredTermEnum} enumeration.
 *
 * <p>This query cannot be used directly; you must subclass
 * it and define {@link #getEnum} to provide a {@link
 * FilteredTermEnum} that iterates through the terms to be
 * matched.
 *
 * <p>NOTE: if {@link #setRewriteMethod} is either
 * {@link #CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE} or {@link
 * #SCORING_BOOLEAN_QUERY_REWRITE}, you may encounter a
 * {@link BooleanQuery.TooManyClauses} exception during
 * searching, which happens when the number of terms to be
 * searched exceeds {@link
 * BooleanQuery#getMaxClauseCount()}.  Setting {@link
 * #setRewriteMethod} to {@link #CONSTANT_SCORE_FILTER_REWRITE}
 * prevents this.
 *
 * <p>The recommended rewrite method is {@link
 * #CONSTANT_SCORE_AUTO_REWRITE_DEFAULT}: it doesn't spend CPU
 * computing unhelpful scores, and it tries to pick the most
 * performant rewrite method given the query. If you
 * need scoring (like {@link FuzzyQuery}, use
 * {@link TopTermsScoringBooleanQueryRewrite} which uses
 * a priority queue to only collect competitive terms
 * and not hit this limitation.
 *
 * Note that {@link QueryParser} produces
 * MultiTermQueries using {@link
 * #CONSTANT_SCORE_AUTO_REWRITE_DEFAULT} by default.
 */
public abstract class MultiTermQuery extends Query {
  protected RewriteMethod rewriteMethod = CONSTANT_SCORE_AUTO_REWRITE_DEFAULT;
  transient int numberOfTerms = 0;

  /** Abstract class that defines how the query is rewritten. */
  public static abstract class RewriteMethod implements Serializable {
    public abstract Query rewrite(IndexReader reader, MultiTermQuery query) throws IOException;
  }

  /** A rewrite method that first creates a private Filter,
   *  by visiting each term in sequence and marking all docs
   *  for that term.  Matching documents are assigned a
   *  constant score equal to the query's boost.
   * 
   *  <p> This method is faster than the BooleanQuery
   *  rewrite methods when the number of matched terms or
   *  matched documents is non-trivial. Also, it will never
   *  hit an errant {@link BooleanQuery.TooManyClauses}
   *  exception.
   *
   *  @see #setRewriteMethod */
  public static final RewriteMethod CONSTANT_SCORE_FILTER_REWRITE = new RewriteMethod() {
    @Override
    public Query rewrite(IndexReader reader, MultiTermQuery query) {
      Query result = new ConstantScoreQuery(new MultiTermQueryWrapperFilter<MultiTermQuery>(query));
      result.setBoost(query.getBoost());
      return result;
    }

    // Make sure we are still a singleton even after deserializing
    protected Object readResolve() {
      return CONSTANT_SCORE_FILTER_REWRITE;
    }
  };

  /** A rewrite method that first translates each term into
   *  {@link BooleanClause.Occur#SHOULD} clause in a
   *  BooleanQuery, and keeps the scores as computed by the
   *  query.  Note that typically such scores are
   *  meaningless to the user, and require non-trivial CPU
   *  to compute, so it's almost always better to use {@link
   *  #CONSTANT_SCORE_AUTO_REWRITE_DEFAULT} instead.
   *
   *  <p>NOTE: This rewrite method will hit {@link
   *  BooleanQuery.TooManyClauses} if the number of terms
   *  exceeds {@link BooleanQuery#getMaxClauseCount}.
   *
   *  @see #setRewriteMethod */
  public final static RewriteMethod SCORING_BOOLEAN_QUERY_REWRITE = ScoringRewrite.SCORING_BOOLEAN_QUERY_REWRITE;
  
  /** Like {@link #SCORING_BOOLEAN_QUERY_REWRITE} except
   *  scores are not computed.  Instead, each matching
   *  document receives a constant score equal to the
   *  query's boost.
   * 
   *  <p>NOTE: This rewrite method will hit {@link
   *  BooleanQuery.TooManyClauses} if the number of terms
   *  exceeds {@link BooleanQuery#getMaxClauseCount}.
   *
   *  @see #setRewriteMethod */
  public final static RewriteMethod CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE = ScoringRewrite.CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE;

  /**
   * A rewrite method that first translates each term into
   * {@link BooleanClause.Occur#SHOULD} clause in a BooleanQuery, and keeps the
   * scores as computed by the query.
   * 
   * <p>
   * This rewrite method only uses the top scoring terms so it will not overflow
   * the boolean max clause count. It is the default rewrite method for
   * {@link FuzzyQuery}.
   * 
   * @see #setRewriteMethod
   */
  public static final class TopTermsScoringBooleanQueryRewrite extends TopTermsRewrite<BooleanQuery> {

    /** 
     * Create a TopTermsScoringBooleanQueryRewrite for 
     * at most <code>size terms.
     * <p>
     * NOTE: if {@link BooleanQuery#getMaxClauseCount} is smaller than 
     * <code>size, then it will be used instead. 
     */
    public TopTermsScoringBooleanQueryRewrite(int size) {
      super(size);
    }
    
    @Override
    protected int getMaxSize() {
      return BooleanQuery.getMaxClauseCount();
    }
    
    @Override
    protected BooleanQuery getTopLevelQuery() {
      return new BooleanQuery(true);
    }
    
    @Override
    protected void addClause(BooleanQuery topLevel, Term term, float boost) {
      final TermQuery tq = new TermQuery(term);
      tq.setBoost(boost);
      topLevel.add(tq, BooleanClause.Occur.SHOULD);
    }
  }
  
  /**
   * A rewrite method that first translates each term into
   * {@link BooleanClause.Occur#SHOULD} clause in a BooleanQuery, but the scores
   * are only computed as the boost.
   * <p>
   * This rewrite method only uses the top scoring terms so it will not overflow
   * the boolean max clause count.
   * 
   * @see #setRewriteMethod
   */
  public static final class TopTermsBoostOnlyBooleanQueryRewrite extends TopTermsRewrite<BooleanQuery> {
    
    /** 
     * Create a TopTermsBoostOnlyBooleanQueryRewrite for 
     * at most <code>size terms.
     * <p>
     * NOTE: if {@link BooleanQuery#getMaxClauseCount} is smaller than 
     * <code>size, then it will be used instead. 
     */
    public TopTermsBoostOnlyBooleanQueryRewrite(int size) {
      super(size);
    }
    
    @Override
    protected int getMaxSize() {
      return BooleanQuery.getMaxClauseCount();
    }
    
    @Override
    protected BooleanQuery getTopLevelQuery() {
      return new BooleanQuery(true);
    }
    
    @Override
    protected void addClause(BooleanQuery topLevel, Term term, float boost) {
      final Query q = new ConstantScoreQuery(new TermQuery(term));
      q.setBoost(boost);
      topLevel.add(q, BooleanClause.Occur.SHOULD);
    }
  }
    
  /** A rewrite method that tries to pick the best
   *  constant-score rewrite method based on term and
   *  document counts from the query.  If both the number of
   *  terms and documents is small enough, then {@link
   *  #CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE} is used.
   *  Otherwise, {@link #CONSTANT_SCORE_FILTER_REWRITE} is
   *  used.
   */
  public static class ConstantScoreAutoRewrite extends org.apache.lucene.search.ConstantScoreAutoRewrite {}

  /** Read-only default instance of {@link
   *  ConstantScoreAutoRewrite}, with {@link
   *  ConstantScoreAutoRewrite#setTermCountCutoff} set to
   *  {@link
   *  ConstantScoreAutoRewrite#DEFAULT_TERM_COUNT_CUTOFF}
   *  and {@link
   *  ConstantScoreAutoRewrite#setDocCountPercent} set to
   *  {@link
   *  ConstantScoreAutoRewrite#DEFAULT_DOC_COUNT_PERCENT}.
   *  Note that you cannot alter the configuration of this
   *  instance; you'll need to create a private instance
   *  instead. */
  public final static RewriteMethod CONSTANT_SCORE_AUTO_REWRITE_DEFAULT = new ConstantScoreAutoRewrite() {
    @Override
    public void setTermCountCutoff(int count) {
      throw new UnsupportedOperationException("Please create a private instance");
    }

    @Override
    public void setDocCountPercent(double percent) {
      throw new UnsupportedOperationException("Please create a private instance");
    }

    // Make sure we are still a singleton even after deserializing
    protected Object readResolve() {
      return CONSTANT_SCORE_AUTO_REWRITE_DEFAULT;
    }
  };

  /**
   * Constructs a query matching terms that cannot be represented with a single
   * Term.
   */
  public MultiTermQuery() {
  }

  /** Construct the enumeration to be used, expanding the pattern term. */
  protected abstract FilteredTermEnum getEnum(IndexReader reader)
      throws IOException;

  /**
   * Expert: Return the number of unique terms visited during execution of the query.
   * If there are many of them, you may consider using another query type
   * or optimize your total term count in index.
   * <p>This method is not thread safe, be sure to only call it when no query is running!
   * If you re-use the same query instance for another
   * search, be sure to first reset the term counter
   * with {@link #clearTotalNumberOfTerms}.
   * <p>On optimized indexes / no MultiReaders, you get the correct number of
   * unique terms for the whole index. Use this number to compare different queries.
   * For non-optimized indexes this number can also be achieved in
   * non-constant-score mode. In constant-score mode you get the total number of
   * terms seeked for all segments / sub-readers.
   * @see #clearTotalNumberOfTerms
   */
  public int getTotalNumberOfTerms() {
    return numberOfTerms;
  }
  
  /**
   * Expert: Resets the counting of unique terms.
   * Do this before executing the query/filter.
   * @see #getTotalNumberOfTerms
   */
  public void clearTotalNumberOfTerms() {
    numberOfTerms = 0;
  }
  
  protected void incTotalNumberOfTerms(int inc) {
    numberOfTerms += inc;
  }

  /**
   * To rewrite to a simpler form, instead return a simpler
   * enum from {@link #getEnum(IndexReader)}.  For example,
   * to rewrite to a single term, return a {@link SingleTermEnum}
   */
  @Override
  public final Query rewrite(IndexReader reader) throws IOException {
    return rewriteMethod.rewrite(reader, this);
  }

  /**
   * @see #setRewriteMethod
   */
  public RewriteMethod getRewriteMethod() {
    return rewriteMethod;
  }

  /**
   * Sets the rewrite method to be used when executing the
   * query.  You can use one of the four core methods, or
   * implement your own subclass of {@link RewriteMethod}. */
  public void setRewriteMethod(RewriteMethod method) {
    rewriteMethod = method;
  }

  @Override
  public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + Float.floatToIntBits(getBoost());
    result = prime * result;
    result += rewriteMethod.hashCode();
    return result;
  }

  @Override
  public boolean equals(Object obj) {
    if (this == obj)
      return true;
    if (obj == null)
      return false;
    if (getClass() != obj.getClass())
      return false;
    MultiTermQuery other = (MultiTermQuery) obj;
    if (Float.floatToIntBits(getBoost()) != Float.floatToIntBits(other.getBoost()))
      return false;
    if (!rewriteMethod.equals(other.rewriteMethod)) {
      return false;
    }
    return true;
  }
 
}

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