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 backtype.storm.state;
  
  import java.util.Map;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import backtype.storm.Config;
  import backtype.storm.task.TopologyContext;
  
  /**
   * A factory for creating {@link State} instances
   */
  public class StateFactory {
      private static final Logger LOG = LoggerFactory.getLogger(StateFactory.class);
  
      private static final String DEFAULT_PROVIDER = "org.apache.storm.state.InMemoryKeyValueStateProvider";
  
      /**
       * Returns a new state instance using the {@link Config#TOPOLOGY_STATE_PROVIDER} or a
       * {@link InMemoryKeyValueState} if no provider is configured.
       *
       * @param namespace the state namespace
       * @param stormConf the storm conf
       * @param context   the topology context
       * @return the state instance
       */
      public static State getState(String namespace, Map stormConf, TopologyContext context) {
          State state;
          try {
              String provider;
              if (stormConf.containsKey(Config.TOPOLOGY_STATE_PROVIDER)) {
                  provider = (String) stormConf.get(Config.TOPOLOGY_STATE_PROVIDER);
              } else {
                  provider = DEFAULT_PROVIDER;
              }
              Class<?> klazz = Class.forName(provider);
              Object object = klazz.newInstance();
              if (object instanceof StateProvider) {
                  state = ((StateProvider) object).newState(namespace, stormConf, context);
              } else {
                  String msg = "Invalid state provider '" + provider +
                          "'. Should implement org.apache.storm.state.StateProvider";
                  LOG.error(msg);
                  throw new RuntimeException(msg);
              }
          } catch (Exception ex) {
              LOG.error("Got exception while loading the state provider", ex);
              throw new RuntimeException(ex);
          }
          return state;
      }
  }
  