Apache Storm技术实战之2

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　　欢迎转载,转载请注明出处,徽沪一郎.
　　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, 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:

• 设置DRPCSpout
  
• 以bolt为入参,创建CoordinatedBolt
  
• 添加JoinResult Bolt
  
• 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=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 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 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