code: /*
   * Copyright © 2014-2017 EntIT Software LLC, a Micro Focus company (L.P.)
   *
   * Licensed 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 io.cloudslang.engine.data;
  
  import org.apache.commons.lang.Validate;
  import org.springframework.util.CollectionUtils;
  
  import java.util.Collections;
  import java.util.HashSet;
  import java.util.Iterator;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Set;
  
  /**
   * User:
   * Date: 18/07/13
   *
   * This class is used for executing queries that contain In clauses.
   * It is needed because databases have a limitation of 1000 (Depending on the database) items per in clause.
   */
  public class SqlInQueryReader {
  
      private final int DATABASE_IN_CLAUSE_LIMIT = 1000;
  
      public <T> List<T> read(Set<String> items, SqlInQueryCallback<T> callback) {
          Validate.notNull(callback);
          if (items == null) {
              return Collections.emptyList();
          } else {
              return readItems(items, callback);
          }
      }
  
      private <T> List<T> readItems(Set<String> items, SqlInQueryCallback<T> callback) {
          Set<String> source = new HashSet<>(items);
          List<T> results = new LinkedList<>();
          do {
              Set<String> itemsToRead = extractAndRemoveUpToLimit(source, DATABASE_IN_CLAUSE_LIMIT);
              List<T> result = callback.readItems(itemsToRead);
              if(result!=null){
                  results.addAll(result);
              }
          } while (!CollectionUtils.isEmpty(source));
          return results;
      }
  
      //Extracts items from source in the ammount set in 'limit' and also removes them from source
      private Set<String> extractAndRemoveUpToLimit(Set<String> source, int limit) {
          Set<String> result = new HashSet<>();
          Iterator<String> iterator = source.iterator();
          while (iterator.hasNext() && result.size() < limit) {
              result.add(iterator.next());
              iterator.remove();
          }
          return result;
      }
  
      public interface SqlInQueryCallback<T> {
          List<T> readItems(Set<String> items);
      }
  
  }
  