Lucene example source code file (TermQuery.java)

This example Lucene source code file (TermQuery.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

complexexplanation, explanation, explanation, indexreader, io, ioexception, ioexception, override, override, string, stringbuilder, term, termquery, termquery, termweight, util

The Lucene TermQuery.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.util.HashSet;
import java.util.Set;

import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermDocs;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.search.Explanation.IDFExplanation;
import org.apache.lucene.util.ReaderUtil;
import org.apache.lucene.util.ToStringUtils;

/** A Query that matches documents containing a term.
  This may be combined with other terms with a {@link BooleanQuery}.
  */
public class TermQuery extends Query {
  private Term term;

  private class TermWeight extends Weight {
    private final Similarity similarity;
    private float value;
    private float idf;
    private float queryNorm;
    private float queryWeight;
    private IDFExplanation idfExp;
    private final Set<Integer> hash;

    public TermWeight(Searcher searcher)
      throws IOException {
      this.similarity = getSimilarity(searcher);
      if (searcher instanceof IndexSearcher) {
        hash = new HashSet<Integer>();
        IndexReader ir = ((IndexSearcher)searcher).getIndexReader();
        final int dfSum[] = new int[1];
        new ReaderUtil.Gather(ir) {
          @Override
          protected void add(int base, IndexReader r) throws IOException {
            int df = r.docFreq(term);
            dfSum[0] += df;
            if (df > 0) {
              hash.add(r.hashCode());
            }
          }
        }.run();

        idfExp = similarity.idfExplain(term, searcher, dfSum[0]);
      } else {
        idfExp = similarity.idfExplain(term, searcher);
        hash = null;
      }

      idf = idfExp.getIdf();
    }

    @Override
    public String toString() { return "weight(" + TermQuery.this + ")"; }

    @Override
    public Query getQuery() { return TermQuery.this; }

    @Override
    public float getValue() { return value; }

    @Override
    public float sumOfSquaredWeights() {
      queryWeight = idf * getBoost();             // compute query weight
      return queryWeight * queryWeight;           // square it
    }

    @Override
    public void normalize(float queryNorm) {
      this.queryNorm = queryNorm;
      queryWeight *= queryNorm;                   // normalize query weight
      value = queryWeight * idf;                  // idf for document
    }

    @Override
    public Scorer scorer(IndexReader reader, boolean scoreDocsInOrder, boolean topScorer) throws IOException {
      if (hash != null && !hash.contains(reader.hashCode())) {
        return null;
      }
      
      TermDocs termDocs = reader.termDocs(term);

      if (termDocs == null)
        return null;

      return new TermScorer(this, termDocs, similarity, reader.norms(term.field()));
    }

    @Override
    public Explanation explain(IndexReader reader, int doc)
      throws IOException {

      ComplexExplanation result = new ComplexExplanation();
      result.setDescription("weight("+getQuery()+" in "+doc+"), product of:");

      Explanation expl = new Explanation(idf, idfExp.explain());

      // explain query weight
      Explanation queryExpl = new Explanation();
      queryExpl.setDescription("queryWeight(" + getQuery() + "), product of:");

      Explanation boostExpl = new Explanation(getBoost(), "boost");
      if (getBoost() != 1.0f)
        queryExpl.addDetail(boostExpl);
      queryExpl.addDetail(expl);

      Explanation queryNormExpl = new Explanation(queryNorm,"queryNorm");
      queryExpl.addDetail(queryNormExpl);

      queryExpl.setValue(boostExpl.getValue() *
                         expl.getValue() *
                         queryNormExpl.getValue());

      result.addDetail(queryExpl);

      // explain field weight
      String field = term.field();
      ComplexExplanation fieldExpl = new ComplexExplanation();
      fieldExpl.setDescription("fieldWeight("+term+" in "+doc+
                               "), product of:");

      Explanation tfExplanation = new Explanation();
      int tf = 0;
      TermDocs termDocs = reader.termDocs(term);
      if (termDocs != null) {
        try {
          if (termDocs.skipTo(doc) && termDocs.doc() == doc) {
            tf = termDocs.freq();
          }
        } finally {
          termDocs.close();
        }
        tfExplanation.setValue(similarity.tf(tf));
        tfExplanation.setDescription("tf(termFreq("+term+")="+tf+")");
      } else {
        tfExplanation.setValue(0.0f);
        tfExplanation.setDescription("no matching term");
      }
      fieldExpl.addDetail(tfExplanation);
      fieldExpl.addDetail(expl);

      Explanation fieldNormExpl = new Explanation();
      byte[] fieldNorms = reader.norms(field);
      float fieldNorm =
        fieldNorms!=null ? similarity.decodeNormValue(fieldNorms[doc]) : 1.0f;
      fieldNormExpl.setValue(fieldNorm);
      fieldNormExpl.setDescription("fieldNorm(field="+field+", doc="+doc+")");
      fieldExpl.addDetail(fieldNormExpl);
      
      fieldExpl.setMatch(Boolean.valueOf(tfExplanation.isMatch()));
      fieldExpl.setValue(tfExplanation.getValue() *
                         expl.getValue() *
                         fieldNormExpl.getValue());

      result.addDetail(fieldExpl);
      result.setMatch(fieldExpl.getMatch());
      
      // combine them
      result.setValue(queryExpl.getValue() * fieldExpl.getValue());

      if (queryExpl.getValue() == 1.0f)
        return fieldExpl;

      return result;
    }
  }

  /** Constructs a query for the term <code>t. */
  public TermQuery(Term t) {
    term = t;
  }

  /** Returns the term of this query. */
  public Term getTerm() { return term; }

  @Override
  public Weight createWeight(Searcher searcher) throws IOException {
    return new TermWeight(searcher);
  }

  @Override
  public void extractTerms(Set<Term> terms) {
    terms.add(getTerm());
  }

  /** Prints a user-readable version of this query. */
  @Override
  public String toString(String field) {
    StringBuilder buffer = new StringBuilder();
    if (!term.field().equals(field)) {
      buffer.append(term.field());
      buffer.append(":");
    }
    buffer.append(term.text());
    buffer.append(ToStringUtils.boost(getBoost()));
    return buffer.toString();
  }

  /** Returns true iff <code>o is equal to this. */
  @Override
  public boolean equals(Object o) {
    if (!(o instanceof TermQuery))
      return false;
    TermQuery other = (TermQuery)o;
    return (this.getBoost() == other.getBoost())
      && this.term.equals(other.term);
  }

  /** Returns a hash code value for this object.*/
  @Override
  public int hashCode() {
    return Float.floatToIntBits(getBoost()) ^ term.hashCode();
  }

}