public static Class<? extends OutputRDD> getOutputFormat(final Class<? extends InputRDD> inputRDD) {
        return INPUT_TO_OUTPUT_CACHE.get(inputRDD);
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
spark-gremlin/src/main/java/org/apache/tinkerpop/gremlin/spark/structure/io/InputOutputHelper.java