Multiple output streams for trident

[alienrobotwizard]

Addresses issue 638 (http://github.com/nathanmarz/storm/issues/638). @mridulj @mrflip

Consider:

Map<String, Fields> outputStreamMapping = new HashMap<String, Fields>();
outputStreamMapping.put("streamA", new Fields("field_in_a"));
outputStreamMapping.put("streamB", new Fields("field_in_b"));

Stream s = topology.newStream("testStream", spout);
StreamCollection multiStream = s.each(
  s.getOutputFields(),
  new DebugMultiStream("streamA", "streamB"),
  new StreamMap(outputStreamMapping)            
  );

Stream streamA = multiStream.getStream("streamA")
streamA.each(new Fields("field_in_a"), new Debug());

[nathanmarz]

I've only glanced at this, but I have two initial comments:

1. This needs tests
2. I'm not so sure about the API. I think that when the multistream each is used, it should return a "MultiStream" object instead of a stream object. And then the MultiStream object can be queried for the particular streams.

[alienrobotwizard]

Nathan,

1. Yes, absolutely. That's the next thing. I just wanted to get the patch out asap since @mridulj was asking about it.
2. The multi each returns a StreamCollection object that has a 'getStream' method. It could just as easily be called MultiStream if that seems like a clearer name.

[alienrobotwizard]

Oh I see the confusion. I've been writing my topologies in jruby which is why I can reuse 's' up there for both a Stream and a StreamCollection. I just did a quick conversion as I was typing. But my previous comment holds, it does return a collection in the way you're asking,