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Lucene example source code file (MultiCollector.java)

This example Lucene source code file (MultiCollector.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

at, collector, collector, illegalargumentexception, io, ioexception, ioexception, multicollector, multicollector, override, override

The Lucene MultiCollector.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.index.IndexReader;
import org.apache.lucene.search.Collector;
import org.apache.lucene.search.Scorer;

/**
 * A {@link Collector} which allows running a search with several
 * {@link Collector}s. It offers a static {@link #wrap} method which accepts a
 * list of collectors and wraps them with {@link MultiCollector}, while
 * filtering out the <code>null null ones.
 */
public class MultiCollector extends Collector {

  /**
   * Wraps a list of {@link Collector}s with a {@link MultiCollector}. This
   * method works as follows:
   * <ul>
   * <li>Filters out the null collectors, so they are not used
   * during search time.
   * <li>If the input contains 1 real collector (i.e. non-null ),
   * it is returned.
   * <li>Otherwise the method returns a {@link MultiCollector} which wraps the
   * non-<code>null ones.
   * </ul>
   * 
   * @throws IllegalArgumentException
   *           if either 0 collectors were input, or all collectors are
   *           <code>null.
   */
  public static Collector wrap(Collector... collectors) {
    // For the user's convenience, we allow null collectors to be passed.
    // However, to improve performance, these null collectors are found
    // and dropped from the array we save for actual collection time.
    int n = 0;
    for (Collector c : collectors) {
      if (c != null) {
        n++;
      }
    }

    if (n == 0) {
      throw new IllegalArgumentException("At least 1 collector must not be null");
    } else if (n == 1) {
      // only 1 Collector - return it.
      Collector col = null;
      for (Collector c : collectors) {
        if (c != null) {
          col = c;
          break;
        }
      }
      return col;
    } else if (n == collectors.length) {
      return new MultiCollector(collectors);
    } else {
      Collector[] colls = new Collector[n];
      n = 0;
      for (Collector c : collectors) {
        if (c != null) {
          colls[n++] = c;
        }
      }
      return new MultiCollector(colls);
    }
  }
  
  private final Collector[] collectors;

  private MultiCollector(Collector... collectors) {
    this.collectors = collectors;
  }

  @Override
  public boolean acceptsDocsOutOfOrder() {
    for (Collector c : collectors) {
      if (!c.acceptsDocsOutOfOrder()) {
        return false;
      }
    }
    return true;
  }

  @Override
  public void collect(int doc) throws IOException {
    for (Collector c : collectors) {
      c.collect(doc);
    }
  }

  @Override
  public void setNextReader(IndexReader reader, int o) throws IOException {
    for (Collector c : collectors) {
      c.setNextReader(reader, o);
    }
  }

  @Override
  public void setScorer(Scorer s) throws IOException {
    for (Collector c : collectors) {
      c.setScorer(s);
    }
  }

}

Other Lucene examples (source code examples)

Here is a short list of links related to this Lucene MultiCollector.java source code file:



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