content: 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</code> 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 <code>null</code> collectors, so they are not used
     * during search time.
     * <li>If the input contains 1 real collector (i.e. non-<code>null</code> ),
     * it is returned.
     * <li>Otherwise the method returns a {@link MultiCollector} which wraps the
     * non-<code>null</code> ones.
     * </ul>
     * 
     * @throws IllegalArgumentException
     *           if either 0 collectors were input, or all collectors are
     *           <code>null</code>.
     */
    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);
      }
    }
  
  }
  