Lucene example source code file (SpanWeight.java)

This example Lucene source code file (SpanWeight.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, complexexplanation, explanation, explanation, hashset, idfexplanation, io, ioexception, ioexception, override, override, searcher, set, spanweight, string, util

The Lucene SpanWeight.java source code

package org.apache.lucene.search.spans;

/**
 * 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 org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.search.*;
import org.apache.lucene.search.Explanation.IDFExplanation;

import java.io.IOException;
import java.util.HashSet;
import java.util.Set;

/**
 * Expert-only.  Public for use by other weight implementations
 */
public class SpanWeight extends Weight {
  protected Similarity similarity;
  protected float value;
  protected float idf;
  protected float queryNorm;
  protected float queryWeight;

  protected Set<Term> terms;
  protected SpanQuery query;
  private IDFExplanation idfExp;

  public SpanWeight(SpanQuery query, Searcher searcher)
    throws IOException {
    this.similarity = query.getSimilarity(searcher);
    this.query = query;
    
    terms=new HashSet<Term>();
    query.extractTerms(terms);
    
    idfExp = similarity.idfExplain(terms, searcher);
    idf = idfExp.getIdf();
  }

  @Override
  public Query getQuery() { return query; }

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

  @Override
  public float sumOfSquaredWeights() throws IOException {
    queryWeight = idf * query.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 {
    return new SpanScorer(query.getSpans(reader), this, similarity, reader
        .norms(query.getField()));
  }

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

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

    Explanation idfExpl =
      new Explanation(idf, "idf(" + field + ": " + idfExp.explain() + ")");

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

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

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

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

    result.addDetail(queryExpl);

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

    Explanation tfExpl = ((SpanScorer)scorer(reader, true, false)).explain(doc);
    fieldExpl.addDetail(tfExpl);
    fieldExpl.addDetail(idfExpl);

    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(tfExpl.isMatch()));
    fieldExpl.setValue(tfExpl.getValue() *
                       idfExpl.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;
  }
}