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Lucene example source code file (ReverseOrdFieldSource.java)

This example Lucene source code file (ReverseOrdFieldSource.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

docvalues, docvalues, io, ioexception, object, override, override, reverseordfieldsource, reverseordfieldsource, string, string, valuesource

The Lucene ReverseOrdFieldSource.java source code

/**
 * 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.
 */

package org.apache.lucene.search.function;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.search.FieldCache;

import java.io.IOException;

/**
 * Expert: obtains the ordinal of the field value from the default Lucene 
 * {@link org.apache.lucene.search.FieldCache FieldCache} using getStringIndex()
 * and reverses the order.
 * <p>
 * The native lucene index order is used to assign an ordinal value for each field value.
 * <p>
 * Field values (terms) are lexicographically ordered by unicode value, and numbered starting at 1.
 * <br>
 * Example of reverse ordinal (rord):
 * <br>If there were only three field values: "apple","banana","pear"
 * <br>then rord("apple")=3, rord("banana")=2, ord("pear")=1
 * <p>
 * WARNING: 
 * rord() depends on the position in an index and can thus change 
 * when other documents are inserted or deleted,
 * or if a MultiSearcher is used. 
 * 
 * @lucene.experimental
 *
 * <p>NOTE: with the switch in 2.9 to segment-based
 * searching, if {@link #getValues} is invoked with a
 * composite (multi-segment) reader, this can easily cause
 * double RAM usage for the values in the FieldCache.  It's
 * best to switch your application to pass only atomic
 * (single segment) readers to this API.</p>
 */

public class ReverseOrdFieldSource extends ValueSource {
  public String field;

  /** 
   * Contructor for a certain field.
   * @param field field whose values reverse order is used.  
   */
  public ReverseOrdFieldSource(String field) {
    this.field = field;
  }

  /*(non-Javadoc) @see org.apache.lucene.search.function.ValueSource#description() */
  @Override
  public String description() {
    return "rord("+field+')';
  }

  /*(non-Javadoc) @see org.apache.lucene.search.function.ValueSource#getValues(org.apache.lucene.index.IndexReader) */
  @Override
  public DocValues getValues(IndexReader reader) throws IOException {
    final FieldCache.StringIndex sindex = FieldCache.DEFAULT.getStringIndex(reader, field);

    final int arr[] = sindex.order;
    final int end = sindex.lookup.length;

    return new DocValues() {
      /*(non-Javadoc) @see org.apache.lucene.search.function.DocValues#floatVal(int) */
      @Override
      public float floatVal(int doc) {
        return (end - arr[doc]);
      }
      /* (non-Javadoc) @see org.apache.lucene.search.function.DocValues#intVal(int) */
      @Override
      public int intVal(int doc) {
        return end - arr[doc];
      }
      /* (non-Javadoc) @see org.apache.lucene.search.function.DocValues#strVal(int) */
      @Override
      public String strVal(int doc) {
        // the string value of the ordinal, not the string itself
        return Integer.toString(intVal(doc));
      }
      /*(non-Javadoc) @see org.apache.lucene.search.function.DocValues#toString(int) */
      @Override
      public String toString(int doc) {
        return description() + '=' + strVal(doc);
      }
      /*(non-Javadoc) @see org.apache.lucene.search.function.DocValues#getInnerArray() */
      @Override
      Object getInnerArray() {
        return arr;
      }
    };
  }

  /*(non-Javadoc) @see java.lang.Object#equals(java.lang.Object) */
  @Override
  public boolean equals(Object o) {
    if (o == this) return true;
    if (o == null) return false;
    if (o.getClass() != ReverseOrdFieldSource.class) return false;
    ReverseOrdFieldSource other = (ReverseOrdFieldSource)o;
    return this.field.equals(other.field); 
  }

  private static final int hcode = ReverseOrdFieldSource.class.hashCode();
  
  /*(non-Javadoc) @see java.lang.Object#hashCode() */
  @Override
  public int hashCode() {
    return hcode + field.hashCode();
  }
}

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