Question

Can anyone point me at a simple, open-source Map/Reduce framework/API for Java? There doesn’t seem to much evidence of such a thing existing, but someone else might know different.

The best I can find is, of course, Hadoop MapReduce, but that fails the “simple” criteria. I don’t need the ability to run distributed jobs, just something to let me run map/reduce-style jobs on a multi-core machine, in a single JVM, using standard Java5-style concurrency.

It’s not a hard thing to write oneself, but I’d rather not have to.

Answer 1

I think it is worth mentioning that these problems are history as of Java 8. An example:

int heaviestBlueBlock =
    blocks.filter(b -> b.getColor() == BLUE)
          .map(Block::getWeight)
          .reduce(0, Integer::max);

In other words: single-node MapReduce is available in Java 8.

For more details, see Brian Goetz’s presentation about project lambda