driver-legacy/src/main/com/mongodb/gridfs/GridFSInputFile.java
protected DBObject createChunk(final Object id, final int currentChunkNumber, final byte[] writeBuffer) {
        return new BasicDBObject("files_id", id)
               .append("n", currentChunkNumber)
               .append("data", writeBuffer);
    }
protected DBObject createChunk(final Object id, final int currentChunkNumber, final byte[] writeBuffer) {
        return new BasicDBObject("files_id", id)
               .append("n", currentChunkNumber)
               .append("data", writeBuffer);
    }
Creates a new chunk of this file. Can be over-ridden, if input files need to be split into chunks using a different mechanism.

@param id                 the file ID
@param currentChunkNumber the unique id for this chunk
@param writeBuffer        the byte array containing the data for this chunk
@return a DBObject representing this chunk.