@Override
    public RecordReader<NullWritable, VertexWritable> createRecordReader(final InputSplit split, final TaskAttemptContext context) throws IOException, InterruptedException {
        RecordReader<NullWritable, VertexWritable> reader = new GraphSONRecordReader();
        reader.initialize(split, context);
        return reader;
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
hadoop-gremlin/src/main/java/org/apache/tinkerpop/gremlin/hadoop/structure/io/graphson/GraphSONInputFormat.java