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