SingleJoinBolt.java

package storm.starter.bolt;

import backtype.storm.Config;
import backtype.storm.generated.GlobalStreamId;
import backtype.storm.task.OutputCollector;
import backtype.storm.task.TopologyContext;
import backtype.storm.topology.OutputFieldsDeclarer;
import backtype.storm.topology.base.BaseRichBolt;
import backtype.storm.tuple.Fields;
import backtype.storm.tuple.Tuple;
import backtype.storm.utils.TimeCacheMap;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

public class SingleJoinBolt extends BaseRichBolt {
    OutputCollector _collector;
    Fields _idFields;
    Fields _outFields;
    int _numSources;
    TimeCacheMap<List<Object>, Map<GlobalStreamId, Tuple>> _pending;
    Map<String, GlobalStreamId> _fieldLocations;
    
    public SingleJoinBolt(Fields outFields) {
        _outFields = outFields;
    }
    
    @Override
    public void prepare(Map conf, TopologyContext context, OutputCollector collector) {
        _fieldLocations = new HashMap<String, GlobalStreamId>();
        _collector = collector;
        int timeout = ((Number) conf.get(Config.TOPOLOGY_MESSAGE_TIMEOUT_SECS)).intValue();
        _pending = new TimeCacheMap<List<Object>, Map<GlobalStreamId, Tuple>>(timeout, new ExpireCallback());
        _numSources = context.getThisSources().size();
        Set<String> idFields = null;
        for(GlobalStreamId source: context.getThisSources().keySet()) {
            Fields fields = context.getComponentOutputFields(source.get_componentId(), source.get_streamId());
            Set<String> setFields = new HashSet<String>(fields.toList());
            if(idFields==null) idFields = setFields;
            else idFields.retainAll(setFields);
            
            for(String outfield: _outFields) {
                for(String sourcefield: fields) {
                    if(outfield.equals(sourcefield)) {
                        _fieldLocations.put(outfield, source);
                    }
                }
            }
        }
        _idFields = new Fields(new ArrayList<String>(idFields));
        
        if(_fieldLocations.size()!=_outFields.size()) {
            throw new RuntimeException("Cannot find all outfields among sources");
        }
    }

    @Override
    public void execute(Tuple tuple) {
        List<Object> id = tuple.select(_idFields);
        GlobalStreamId streamId = new GlobalStreamId(tuple.getSourceComponent(), tuple.getSourceStreamId());
        if(!_pending.containsKey(id)) {
            _pending.put(id, new HashMap<GlobalStreamId, Tuple>());            
        }
        Map<GlobalStreamId, Tuple> parts = _pending.get(id);
        if(parts.containsKey(streamId)) throw new RuntimeException("Received same side of single join twice");
        parts.put(streamId, tuple);
        if(parts.size()==_numSources) {
            _pending.remove(id);
            List<Object> joinResult = new ArrayList<Object>();
            for(String outField: _outFields) {
                GlobalStreamId loc = _fieldLocations.get(outField);
                joinResult.add(parts.get(loc).getValueByField(outField));
            }
            _collector.emit(new ArrayList<Tuple>(parts.values()), joinResult);
            
            for(Tuple part: parts.values()) {
                _collector.ack(part);
            }
        }
    }

    @Override
    public void declareOutputFields(OutputFieldsDeclarer declarer) {
        declarer.declare(_outFields);
    }    
    
    private class ExpireCallback implements TimeCacheMap.ExpiredCallback<List<Object>, Map<GlobalStreamId, Tuple>> {
        @Override
        public void expire(List<Object> id, Map<GlobalStreamId, Tuple> tuples) {
            for(Tuple tuple: tuples.values()) {
                _collector.fail(tuple);
            }
        }        
    }
}