examples/storm-starter/src/jvm/storm/starter/bolt/AbstractRankerBolt.java

/**
 * 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.starter.bolt;

import backtype.storm.Config;
import backtype.storm.topology.BasicOutputCollector;
import backtype.storm.topology.OutputFieldsDeclarer;
import backtype.storm.topology.base.BaseBasicBolt;
import backtype.storm.tuple.Fields;
import backtype.storm.tuple.Tuple;
import backtype.storm.tuple.Values;
import backtype.storm.utils.TupleUtils;
import org.apache.log4j.Logger;
import storm.starter.tools.Rankings;

import java.util.HashMap;
import java.util.Map;

/**
 * This abstract bolt provides the basic behavior of bolts that rank objects according to their count.
 * <p></p>
 * It uses a template method design pattern for {@link AbstractRankerBolt#execute(Tuple, BasicOutputCollector)} to allow
 * actual bolt implementations to specify how incoming tuples are processed, i.e. how the objects embedded within those
 * tuples are retrieved and counted.
 */
public abstract class AbstractRankerBolt extends BaseBasicBolt {

  private static final long serialVersionUID = 4931640198501530202L;
  private static final int DEFAULT_EMIT_FREQUENCY_IN_SECONDS = 2;
  private static final int DEFAULT_COUNT = 10;

  private final int emitFrequencyInSeconds;
  private final int count;
  private final Rankings rankings;

  public AbstractRankerBolt() {
    this(DEFAULT_COUNT, DEFAULT_EMIT_FREQUENCY_IN_SECONDS);
  }

  public AbstractRankerBolt(int topN) {
    this(topN, DEFAULT_EMIT_FREQUENCY_IN_SECONDS);
  }

  public AbstractRankerBolt(int topN, int emitFrequencyInSeconds) {
    if (topN < 1) {
      throw new IllegalArgumentException("topN must be >= 1 (you requested " + topN + ")");
    }
    if (emitFrequencyInSeconds < 1) {
      throw new IllegalArgumentException(
          "The emit frequency must be >= 1 seconds (you requested " + emitFrequencyInSeconds + " seconds)");
    }
    count = topN;
    this.emitFrequencyInSeconds = emitFrequencyInSeconds;
    rankings = new Rankings(count);
  }

  protected Rankings getRankings() {
    return rankings;
  }

  /**
   * This method functions as a template method (design pattern).
   */
  @Override
  public final void execute(Tuple tuple, BasicOutputCollector collector) {
    if (TupleUtils.isTick(tuple)) {
      getLogger().debug("Received tick tuple, triggering emit of current rankings");
      emitRankings(collector);
    }
    else {
      updateRankingsWithTuple(tuple);
    }
  }

  abstract void updateRankingsWithTuple(Tuple tuple);

  private void emitRankings(BasicOutputCollector collector) {
    collector.emit(new Values(rankings.copy()));
    getLogger().debug("Rankings: " + rankings);
  }

  @Override
  public void declareOutputFields(OutputFieldsDeclarer declarer) {
    declarer.declare(new Fields("rankings"));
  }

  @Override
  public Map<String, Object> getComponentConfiguration() {
    Map<String, Object> conf = new HashMap<String, Object>();
    conf.put(Config.TOPOLOGY_TICK_TUPLE_FREQ_SECS, emitFrequencyInSeconds);
    return conf;
  }

  abstract Logger getLogger();
}