content: package org.apache.solr.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 org.apache.lucene.search.Collector;
  import org.apache.lucene.search.Sort;
  import org.apache.solr.schema.SchemaField;
  
  import java.io.IOException;
  import java.util.List;
  
  /**
   * Defines a grouping command.
   * This is an abstraction on how the {@link Collector} instances are created
   * and how the results are retrieved from the {@link Collector} instances.
   *
   * @lucene.experimental
   */
  public interface Command<T> {
  
    /**
     * Returns a list of {@link Collector} instances to be
     * included in the search based on the .
     *
     * @return a list of {@link Collector} instances
     * @throws IOException If I/O related errors occur
     */
    List<Collector> create() throws IOException;
  
    /**
     * Returns the results that the collectors created
     * by {@link #create()} contain after a search has been executed.
     *
     * @return The results of the collectors
     */
    T result();
  
    /**
     * @return The key of this command to uniquely identify itself
     */
    String getKey();
  
    /**
     * @return The group sort (overall sort)
     */
    Sort getGroupSort();
  
    /**
     * @return The sort inside a group
     */
    Sort getSortWithinGroup();
  
  }
  