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Lucene example source code file (TermFirstPassGroupingCollector.java)

This example Lucene source code file (TermFirstPassGroupingCollector.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

abstractfirstpassgroupingcollector, io, ioexception, ioexception, override, override, sort, string, string, termfirstpassgroupingcollector, termfirstpassgroupingcollector

The Lucene TermFirstPassGroupingCollector.java source code

package org.apache.lucene.search.grouping;

/**
 * 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.index.IndexReader;
import org.apache.lucene.search.FieldCache;
import org.apache.lucene.search.Sort;

/**
 * Concrete implementation of {@link AbstractFirstPassGroupingCollector} that groups based on
 * field values and more specifically uses {@link org.apache.lucene.search.FieldCache.StringIndex}
 * to collect groups.
 *
 * @lucene.experimental
 */
public class TermFirstPassGroupingCollector extends AbstractFirstPassGroupingCollector<String> {

  private FieldCache.StringIndex index;

  private String groupField;

  /**
   * Create the first pass collector.
   *
   *  @param groupField The field used to group
   *    documents. This field must be single-valued and
   *    indexed (FieldCache is used to access its value
   *    per-document).
   *  @param groupSort The {@link Sort} used to sort the
   *    groups.  The top sorted document within each group
   *    according to groupSort, determines how that group
   *    sorts against other groups.  This must be non-null,
   *    ie, if you want to groupSort by relevance use
   *    Sort.RELEVANCE.
   *  @param topNGroups How many top groups to keep.
   *  @throws IOException When I/O related errors occur
   */
  public TermFirstPassGroupingCollector(String groupField, Sort groupSort, int topNGroups) throws IOException {
    super(groupSort, topNGroups);
    this.groupField = groupField;
  }

  @Override
  protected String getDocGroupValue(int doc) {
    final int ord = index.order[doc];
    return ord == 0 ? null : index.lookup[ord];
  }

  @Override
  protected String copyDocGroupValue(String groupValue, String reuse) {
    return groupValue;
  }

  @Override
  public void setNextReader(IndexReader reader, int docBase) throws IOException {
    super.setNextReader(reader, docBase);
    index = FieldCache.DEFAULT.getStringIndex(reader, groupField);
  }
}

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