examples/storm-starter/src/jvm/org/apache/storm/starter/bolt/RollingCountAggBolt.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 org.apache.storm.starter.bolt;

import java.util.HashMap;
import java.util.Map;
import org.apache.log4j.Logger;
import org.apache.storm.task.OutputCollector;
import org.apache.storm.task.TopologyContext;
import org.apache.storm.topology.OutputFieldsDeclarer;
import org.apache.storm.topology.base.BaseRichBolt;
import org.apache.storm.tuple.Fields;
import org.apache.storm.tuple.Tuple;
import org.apache.storm.tuple.Values;

/**
 * This bolt aggregates counts from multiple upstream bolts.
 */
public class RollingCountAggBolt extends BaseRichBolt {
    private static final long serialVersionUID = 5537727428628598519L;
    private static final Logger LOG = Logger.getLogger(RollingCountAggBolt.class);
    //Mapping of key->upstreamBolt->count
    private Map<Object, Map<Integer, Long>> counts = new HashMap<Object, Map<Integer, Long>>();
    private OutputCollector collector;


    @Override
    public void prepare(Map<String, Object> topoConf, TopologyContext context, OutputCollector collector) {
        this.collector = collector;
    }

    @Override
    public void execute(Tuple tuple) {
        Object obj = tuple.getValue(0);
        long count = tuple.getLong(1);
        int source = tuple.getSourceTask();
        Map<Integer, Long> subCounts = counts.get(obj);
        if (subCounts == null) {
            subCounts = new HashMap<Integer, Long>();
            counts.put(obj, subCounts);
        }
        //Update the current count for this object
        subCounts.put(source, count);
        //Output the sum of all the known counts so for this key
        long sum = 0;
        for (Long val : subCounts.values()) {
            sum += val;
        }
        collector.emit(new Values(obj, sum));
    }

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