content: /**
   * 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.
   */
  package storm.trident.state.map;
  
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import storm.trident.util.LRUMap;
  
  /**
   * Useful to layer over a map that communicates with a database. you generally layer opaque map over this over your database store
   * 
   * @author nathan
   * @param <T>
   */
  public class CachedMap<T> implements IBackingMap<T> {
      LRUMap<List<Object>, T> _cache;
      IBackingMap<T> _delegate;
  
      public CachedMap(IBackingMap<T> delegate, int cacheSize) {
          _cache = new LRUMap<List<Object>, T>(cacheSize);
          _delegate = delegate;
      }
  
      @Override
      public List<T> multiGet(List<List<Object>> keys) {
          Map<List<Object>, T> results = new HashMap<List<Object>, T>();
          List<List<Object>> toGet = new ArrayList<List<Object>>();
          for (List<Object> key : keys) {
              if (_cache.containsKey(key)) {
                  results.put(key, _cache.get(key));
              } else {
                  toGet.add(key);
              }
          }
  
          List<T> fetchedVals = _delegate.multiGet(toGet);
          for (int i = 0; i < toGet.size(); i++) {
              List<Object> key = toGet.get(i);
              T val = fetchedVals.get(i);
              _cache.put(key, val);
              results.put(key, val);
          }
  
          List<T> ret = new ArrayList<T>(keys.size());
          for (List<Object> key : keys) {
              ret.add(results.get(key));
          }
          return ret;
      }
  
      @Override
      public void multiPut(List<List<Object>> keys, List<T> values) {
          cache(keys, values);
          _delegate.multiPut(keys, values);
      }
  
      private void cache(List<List<Object>> keys, List<T> values) {
          for (int i = 0; i < keys.size(); i++) {
              _cache.put(keys.get(i), values.get(i));
          }
      }
  
  }
  