SmartIterator.java

/**
 * Licensed to The Apereo Foundation under one or more contributor license
 * agreements. See the NOTICE file distributed with this work for additional
 * information regarding copyright ownership.
 *
 *
 * The Apereo Foundation licenses this file to you under the Educational
 * Community 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://opensource.org/licenses/ecl2.txt
 *
 * 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 org.opencastproject.util;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

/**
 * Utility class for applying limit and offset to a map or collection
 */
public class SmartIterator<A> {
  private int limit;
  private int offset;
  private Iterator<?> iterator;

  public SmartIterator(int limit, int offset) {
    this.limit = limit;
    this.offset = offset;
  }

  /**
   * Apply limit and offset to a map of value type {@link A}
   *
   * @param map
   *          the map
   * @return the filtered map
   */
  public Map<String, A> applyLimitAndOffset(Map<String, A> map) {
    iterator = map.entrySet().iterator();

    Map<String, A> filteredMap = new LinkedHashMap<String, A>();
    int i = 0;
    while (isRecordRequired(filteredMap.size())) {
      Entry<String, A> item = (Entry<String, A>) iterator.next();
      if (i++ >= offset) {
        filteredMap.put(item.getKey(), item.getValue());
      }
    }
    return filteredMap;
  }

  private boolean isRecordRequired(int filteredMapSize) {
    return (filteredMapSize < limit || limit == 0) && iterator.hasNext();
  }

  /**
   * Apply limit and offset to a collection of type {@link A}
   *
   * @param unfilteredCollection
   *          the collection
   * @return the filtered list
   */
  public List<A> applyLimitAndOffset(Collection<A> unfilteredCollection) {
    iterator = unfilteredCollection.iterator();
    List<A> filteredList = new ArrayList<A>();
    int i = 0;
    while (isRecordRequired(filteredList.size())) {
      A nextItem = (A) iterator.next();
      if (i++ >= offset) {
        filteredList.add(nextItem);
      }
    }
    return filteredList;
  }
}