driver-core/src/main/com/mongodb/operation/MapReduceWithInlineResultsOperation.java
@Override
    @SuppressWarnings("unchecked")
    public MapReduceBatchCursor<T> execute(final ReadBinding binding) {
        return executeCommand(binding, namespace.getDatabaseName(), getCommandCreator(binding.getSessionContext()),
                CommandResultDocumentCodec.create(decoder, "results"), transformer(), false);
    }
@Override
    @SuppressWarnings("unchecked")
    public MapReduceBatchCursor<T> execute(final ReadBinding binding) {
        return executeCommand(binding, namespace.getDatabaseName(), getCommandCreator(binding.getSessionContext()),
                CommandResultDocumentCodec.create(decoder, "results"), transformer(), false);
    }
Executing this will return a cursor with your results and the statistics in.

@param binding the binding
@return a MapReduceCursor that can be iterated over to find all the results of the Map Reduce operation.