Patch w/ ChainingCollector, a matching test and CHANGES entry.

Committed revision 995373 (3x).
Committed revision 995375 (trunk).

I've received some offline comments about the name - MultiCollector (the original name in our code) seems to be more aligned w/ other Lucene classes, like MultiReader/Searcher. I personally think ChainingCollector is fine as well (and describes better what this class is about), however for consistency I think I'll rename it to MultiCollector. Any objections?

Heh - Solr added a MultiCollector a few weeks ago (and it does exactly the same thing).
As far as naming, I agree this isn't a chaining collector, but a branching collector (and MultiCollector is a better name).

Solr's version also has this, which simplifies building a list of collectors and then creating a single collector:

  public static Collector wrap(List<? extends Collector> collectors) {
    return collectors.size() == 1 ? collectors.get(0) : new MultiCollector(collectors);  
  }

We should consolidate these two versions of course.

Heh - Solr added a MultiCollector a few weeks ago

Nice .

... MultiCollector is a better name

I will rename.

Solr's version also has this

That makes sense. If you eventually run w/ a single Collector, no need to have MultiCollector in the middle. I'll change MC then to have a private ctor and a static create method. I would like though for the method to receive a Collector... rather than List, because I think it simplifies matters on the application's end. And create will filter out all the null ones ...

I'll post a patch soon.

Might need 1-2 iterations, so reopening.

Name changes + static wrap.

+1 looks good!

Committed revision 996058 (3x).
Committed revision 996060 (trunk).

Bulk close for 3.1