Apache Storm Component Guide
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Core Storm Example: RollingTopWords Topology

The RollingTopWords.java is included with storm-starter.

package storm.starter;

import org.apache.storm.Config;
import org.apache.storm.testing.TestWordSpout;
import org.apache.storm.topology.TopologyBuilder;
import org.apache.storm.tuple.Fields;
import storm.starter.bolt.IntermediateRankingsBolt;
import storm.starter.bolt.RollingCountBolt;
import storm.starter.bolt.TotalRankingsBolt;
import storm.starter.util.StormRunner;

* This topology does a continuous computation of the top N words that the topology has seen in terms of cardinality.
* The top N computation is done in a completely scalable way, and a similar approach could be used to compute things
* like trending topics or trending images on Twitter.
public class RollingTopWords {

 private static final int DEFAULT_RUNTIME_IN_SECONDS = 60;
 private static final int TOP_N = 5;

 private final TopologyBuilder builder;
 private final String topologyName;
 private final Config topologyConfig;
 private final int runtimeInSeconds;

 public RollingTopWords() throws InterruptedException {
   builder = new TopologyBuilder();
   topologyName = "slidingWindowCounts";
   topologyConfig = createTopologyConfiguration();


 private static Config createTopologyConfiguration() {
   Config conf = new Config();
   return conf;

 private void wireTopology() throws InterruptedException {
   String spoutId = "wordGenerator";
   String counterId = "counter";
   String intermediateRankerId = "intermediateRanker";
   String totalRankerId = "finalRanker";
   builder.setSpout(spoutId, new TestWordSpout(), 5);
   builder.setBolt(counterId, new RollingCountBolt(9, 3), 4).fieldsGrouping(spoutId, new Fields("word"));
   builder.setBolt(intermediateRankerId, new IntermediateRankingsBolt(TOP_N), 4).fieldsGrouping(counterId, new Fields( "obj"));
   builder.setBolt(totalRankerId, new TotalRankingsBolt(TOP_N)).globalGrouping(intermediateRankerId);

 public void run() throws InterruptedException {
   StormRunner.runTopologyLocally(builder.createTopology(), topologyName, topologyConfig, runtimeInSeconds);

 public static void main(String[] args) throws Exception {
   new RollingTopWords().run();