public class Demo {

    public static void main(String[] args) throws UnknownHostException {
        MongoClient mongo = new MongoClient("localhost");
        DB db = mongo.getDB("gridDB");
        GridFS gridfs = new GridFS(db);

        GridFSInputFile input = gridfs.createFile(new byte[42]);
        input.setContentType("griffins");
        input.save();

        String id = input.getId().toString();

        GridFSDBFile saved = gridfs.findOne(new ObjectId(id));
        System.out.println("saved: " + saved); // should not be null
    }
}