/**
* 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.List;
import java.util.Map;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import backtype.storm.task.OutputCollector;
import backtype.storm.task.TopologyContext;
import backtype.storm.topology.OutputFieldsDeclarer;
import backtype.storm.topology.base.BaseWindowedBolt;
import backtype.storm.tuple.Fields;
import backtype.storm.tuple.Tuple;
import backtype.storm.tuple.Values;
import backtype.storm.windowing.TupleWindow;
/**
* Computes sliding window sum
*/
public class SlidingWindowSumBolt extends BaseWindowedBolt {
private static final Logger LOG = LoggerFactory.getLogger(SlidingWindowSumBolt.class);
private int sum = 0;
private OutputCollector collector;
@Override
public void prepare(Map stormConf, TopologyContext context, OutputCollector collector) {
this.collector = collector;
}
@Override
public void execute(TupleWindow inputWindow) {
/*
* The inputWindow gives a view of (a) all the events in the window (b)
* events that expired since last activation of the window (c) events
* that newly arrived since last activation of the window
*/
List<Tuple> tuplesInWindow = inputWindow.get();
List<Tuple> newTuples = inputWindow.getNew();
List<Tuple> expiredTuples = inputWindow.getExpired();
LOG.debug("Events in current window: " + tuplesInWindow.size());
/*
* Instead of iterating over all the tuples in the window to compute the
* sum, the values for the new events are added and old events are
* subtracted. Similar optimizations might be possible in other
* windowing computations.
*/
for (Tuple tuple : newTuples) {
sum += (int) tuple.getValue(0);
}
for (Tuple tuple : expiredTuples) {
sum -= (int) tuple.getValue(0);
}
collector.emit(new Values(sum));
}
@Override
public void declareOutputFields(OutputFieldsDeclarer declarer) {
declarer.declare(new Fields("sum"));
}
}