code: /*******************************************************************************
   * Copyright 2018 572682
   * 
   * 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 us.dot.its.jpo.ode.wrapper;
  
  import java.util.Arrays;
  import java.util.concurrent.Executors;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * @author 572682
   *
   *         This abstract class provides a basic service that subscribes to one
   *         or more topics and process the received messages in the derived
   *         classes.
   * 
   * @param <K>
   *           Message Key type
   * @param <S>
   *           Received Message Value Type
   */
  public abstract class AbstractSubscriberProcessor<K, S> extends MessageProcessor<K, S> {
  
     private Logger logger = LoggerFactory.getLogger(this.getClass());
     protected int messagesConsumed = 0;
  
     /**
      * Starts a Kafka listener that runs call() every time a new msg arrives
      * 
      * @param consumer
      * @param inputTopics
      */
     public void start(MessageConsumer<K, S> consumer, String... inputTopics) {
        logger.info("Subscribing to {}", Arrays.asList(inputTopics).toString());
  
        Executors.newSingleThreadExecutor().submit(new Runnable() {
           @Override
           public void run() {
              consumer.subscribe(inputTopics);
           }
        });
     }
  
     @Override
     public Object call() {
        messagesConsumed++;
  
        S consumedData = getRecord().value();
  
        return process(consumedData);
     }
  
     protected abstract Object process(S consumedData);
  
  }
  