Apache Storm技术实战之2 -- BasicDRPCTopology

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本文通过BasicDRPCTopology的实例来分析DRPCTopology在提交的时候, Topology中究竟含有哪些内容?

BasicDRPCTopology

main函数

DRPC 分布式远程调用(这个说法有意思,远程调用本来就是分布的,何须再加个D, <头文字D>看多了, :)

public static void main(String[] args) throws Exception {
    LinearDRPCTopologyBuilder builder = new LinearDRPCTopologyBuilder("exclamation");
    builder.addBolt(new ExclaimBolt(), 3);

    Config conf = new Config();

    if (args == null || args.length == 0) {
      LocalDRPC drpc = new LocalDRPC();
      LocalCluster cluster = new LocalCluster();

      cluster.submitTopology("drpc-demo", conf, builder.createLocalTopology(drpc));

      for (String word : new String[]{ "hello", "goodbye" }) {
        System.out.println("Result for \"" + word + "\": " + drpc.execute("exclamation", word));
      }

      cluster.shutdown();
      drpc.shutdown();
    }
    else {
      conf.setNumWorkers(3);
      StormSubmitter.submitTopology(args[0], conf, builder.createRemoteTopology());
    }
  }

问题: 上面的代码中只是添加了一个bolt,并没有设定Spout. 我们知道一个topology中最起码得有一个Spout,那么这里的Spout又隐身于何处呢?

关键的地方就在builder.createLocalTopology, 调用关系如下

• LinearDRPCTopologyBuilder::createLocalTopology
  • 　　LinearDRPCTopologyBuilder::createTopology()
    • 　　LinearDRPCTopologyBuilder::createTopology(new DRPCSpout(_function))

原来DRPCTopology中使用的Spout是DRPCSpout.

LinearDRPCTopology::createTopology

既然代码已经读到此处,何不再进一步看看createTopology的实现.

简要说明一下该段代码的处理逻辑:

1. 设置DRPCSpout
2. 以bolt为入参,创建CoordinatedBolt
3. 添加JoinResult Bolt
4. 添加ReturnResult Bolt: ReturnResultBolt连接到DRPCServer,并返回结果

    private StormTopology createTopology(DRPCSpout spout) {
        final String SPOUT_ID = "spout";
        final String PREPARE_ID = "prepare-request";

        TopologyBuilder builder = new TopologyBuilder();
        builder.setSpout(SPOUT_ID, spout);
        builder.setBolt(PREPARE_ID, new PrepareRequest())
                .noneGrouping(SPOUT_ID);
        int i=0;
        for(; i<_components.size();i++) {
            Component component = _components.get(i);

            Map<String, SourceArgs> source = new HashMap<String, SourceArgs>();
            if (i==1) {
                source.put(boltId(i-1), SourceArgs.single());
            } else if (i>=2) {
                source.put(boltId(i-1), SourceArgs.all());
            }
            IdStreamSpec idSpec = null;
            if(i==_components.size()-1 && component.bolt instanceof FinishedCallback) {
                idSpec = IdStreamSpec.makeDetectSpec(PREPARE_ID, PrepareRequest.ID_STREAM);
            }
            BoltDeclarer declarer = builder.setBolt(
                    boltId(i),
                    new CoordinatedBolt(component.bolt, source, idSpec),
                    component.parallelism);

            for(Map conf: component.componentConfs) {
                declarer.addConfigurations(conf);
            }

            if(idSpec!=null) {
                declarer.fieldsGrouping(idSpec.getGlobalStreamId().get_componentId(), PrepareRequest.ID_STREAM, new Fields("request"));
            }
            if(i==0 && component.declarations.isEmpty()) {
                declarer.noneGrouping(PREPARE_ID, PrepareRequest.ARGS_STREAM);
            } else {
                String prevId;
                if(i==0) {
                    prevId = PREPARE_ID;
                } else {
                    prevId = boltId(i-1);
                }
                for(InputDeclaration declaration: component.declarations) {
                    declaration.declare(prevId, declarer);
                }
            }
            if(i>0) {
                declarer.directGrouping(boltId(i-1), Constants.COORDINATED_STREAM_ID);
            }
        }

        IRichBolt lastBolt = _components.get(_components.size()-1).bolt;
        OutputFieldsGetter getter = new OutputFieldsGetter();
        lastBolt.declareOutputFields(getter);
        Map<String, StreamInfo> streams = getter.getFieldsDeclaration();
        if(streams.size()!=1) {
            throw new RuntimeException("Must declare exactly one stream from last bolt in LinearDRPCTopology");
        }
        String outputStream = streams.keySet().iterator().next();
        List<String> fields = streams.get(outputStream).get_output_fields();
        if(fields.size()!=2) {
            throw new RuntimeException("Output stream of last component in LinearDRPCTopology must contain exactly two fields. The first should be the request id, and the second should be the result.");
        }

        builder.setBolt(boltId(i), new JoinResult(PREPARE_ID))
                .fieldsGrouping(boltId(i-1), outputStream, new Fields(fields.get(0)))
                .fieldsGrouping(PREPARE_ID, PrepareRequest.RETURN_STREAM, new Fields("request"));
        i++;
        builder.setBolt(boltId(i), new ReturnResults())
                .noneGrouping(boltId(i-1));
        return builder.createTopology();
    }

Bolt

处理逻辑: 在接收到的每一个单词后面添加'!'.

 public static class ExclaimBolt extends BaseBasicBolt {
    @Override
    public void execute(Tuple tuple, BasicOutputCollector collector) {
      String input = tuple.getString(1);
      collector.emit(new Values(tuple.getValue(0), input + "!"));
    }

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

运行

java -cp $(lein classpath) storm.starter.BasicDRPCTopology