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Lucene example source code file (Scorer.java)

This example Lucene source code file (Scorer.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

c, deprecated, io, ioexception, ioexception, no_more_docs, query, query, s, s, scorer, scorer, scorervisitor, similarity, unsupportedoperationexception

The Lucene Scorer.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.search.BooleanClause.Occur;

/**
 * Expert: Common scoring functionality for different types of queries.
 *
 * <p>
 * A <code>Scorer iterates over documents matching a
 * query in increasing order of doc Id.
 * </p>
 * <p>
 * Document scores are computed using a given <code>Similarity
 * implementation.
 * </p>
 *
 * <p>NOTE: The values Float.Nan,
 * Float.NEGATIVE_INFINITY and Float.POSITIVE_INFINITY are
 * not valid scores.  Certain collectors (eg {@link
 * TopScoreDocCollector}) will not properly collect hits
 * with these scores.
 */
public abstract class Scorer extends DocIdSetIterator {
  private final Similarity similarity;
  protected final Weight weight;

  /**
   * Constructs a Scorer
   * @param weight The scorers <code>Weight.
   */
  protected Scorer(Weight weight) {
    this(null, weight);
  }
  
  /** Constructs a Scorer.
   * @param similarity The <code>Similarity implementation used by this scorer.
   * @deprecated Use {@link #Scorer(Weight)} instead.
   */
  @Deprecated
  protected Scorer(Similarity similarity) {
    this(similarity, null);
  }
  
  /**
   * Constructs a Scorer
   * @param similarity The <code>Similarity implementation used by this scorer.
   * @param weight The scorers <code>Weight
   * @deprecated Use {@link #Scorer(Weight)} instead.
   */
  @Deprecated
  protected Scorer(Similarity similarity, Weight weight) {
    this.similarity = similarity;
    this.weight = weight;
  }

  /** Returns the Similarity implementation used by this scorer. 
   * @deprecated Store any Similarity you might need privately in your implementation instead.
   */
  @Deprecated
  public Similarity getSimilarity() {
    return this.similarity;
  }

  /** Scores and collects all matching documents.
   * @param collector The collector to which all matching documents are passed.
   */
  public void score(Collector collector) throws IOException {
    collector.setScorer(this);
    int doc;
    while ((doc = nextDoc()) != NO_MORE_DOCS) {
      collector.collect(doc);
    }
  }

  /**
   * Expert: Collects matching documents in a range. Hook for optimization.
   * Note, <code>firstDocID is added to ensure that {@link #nextDoc()}
   * was called before this method.
   *
   * <p>NOTE: Because of backwards compatibility, this method is still
   * declared as <b>protected, but it is intended to be public,
   * because it's called from other classes (like BooleanScorer).
   * If you subclass {@code Scorer}, you should declare the overridden method
   * as public to ease transition to Lucene 4.0, where it will be public.</p>
   * 
   * @param collector
   *          The collector to which all matching documents are passed.
   * @param max
   *          Do not score documents past this.
   * @param firstDocID
   *          The first document ID (ensures {@link #nextDoc()} is called before
   *          this method.
   * @return true if more matching documents may remain.
   */
  protected boolean score(Collector collector, int max, int firstDocID) throws IOException {
    collector.setScorer(this);
    int doc = firstDocID;
    while (doc < max) {
      collector.collect(doc);
      doc = nextDoc();
    }
    return doc != NO_MORE_DOCS;
  }
  
  /** Returns the score of the current document matching the query.
   * Initially invalid, until {@link #nextDoc()} or {@link #advance(int)}
   * is called the first time, or when called from within
   * {@link Collector#collect}.
   */
  public abstract float score() throws IOException;

  /** Returns number of matches for the current document.
   *  This returns a float (not int) because
   *  SloppyPhraseScorer discounts its freq according to how
   *  "sloppy" the match was.
   *
   * @lucene.experimental */
  public float freq() throws IOException {
    throw new UnsupportedOperationException(this + " does not implement freq()");
  }

  /**
   * A callback to gather information from a scorer and its sub-scorers. Each
   * the top-level scorer as well as each of its sub-scorers are passed to
   * either one of the visit methods depending on their boolean relationship in
   * the query.
   * @lucene.experimental
   */
  public static abstract class ScorerVisitor<P extends Query, C extends Query, S extends Scorer> {
    /**
     * Invoked for all optional scorer 
     * 
     * @param parent the parent query of the child query or <code>null if the child is a top-level query
     * @param child the query of the currently visited scorer
     * @param scorer the current scorer
     */
    public void visitOptional(P parent, C child, S scorer) {}
    
    /**
     * Invoked for all required scorer 
     * 
     * @param parent the parent query of the child query or <code>null if the child is a top-level query
     * @param child the query of the currently visited scorer
     * @param scorer the current scorer
     */
    public void visitRequired(P parent, C child, S scorer) {}
    
    /**
     * Invoked for all prohibited scorer 
     * 
     * @param parent the parent query of the child query or <code>null if the child is a top-level query
     * @param child the query of the currently visited scorer
     * @param scorer the current scorer
     */
    public void visitProhibited(P parent, C child, S scorer) {}
  } 

  /**
   * Expert: call this to gather details for all sub-scorers for this query.
   * This can be used, in conjunction with a custom {@link Collector} to gather
   * details about how each sub-query matched the current hit.
   * 
   * @param visitor a callback executed for each sub-scorer
   * @lucene.experimental
   */
  public void visitScorers(ScorerVisitor<Query, Query, Scorer> visitor) {
    visitSubScorers(null, Occur.MUST/*must id default*/, visitor);
  }

  /**
   * {@link Scorer} subclasses should implement this method if the subclass
   * itself contains multiple scorers to support gathering details for
   * sub-scorers via {@link ScorerVisitor}
   * <p>
   * Note: this method will throw {@link UnsupportedOperationException} if no
   * associated {@link Weight} instance is provided to
   * {@link #Scorer(Weight)}
   * </p>
   * 
   * @lucene.experimental
   */
  protected void visitSubScorers(Query parent, Occur relationship,
      ScorerVisitor<Query, Query, Scorer> visitor) {
    if (weight == null)
      throw new UnsupportedOperationException();

    final Query q = weight.getQuery();
    switch (relationship) {
    case MUST:
      visitor.visitRequired(parent, q, this);
      break;
    case MUST_NOT:
      visitor.visitProhibited(parent, q, this);
      break;
    case SHOULD:
      visitor.visitOptional(parent, q, this);
      break;
    }
  }
}

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