When you are struggling for making the dataframe from List<List<Object>> get here.

convert_to_ROW_from_List.java

// suppose we have the list like this (not to run but just idea)
List<List<Integer>> data = [
  [1, 2, 3],
  [2, 3, 4],
  [3, 4, 5]
];

// Now to convert each List<Integer> to Row so that can be used to make DF
List<Row> rows = new ArrayList<>();
for (List<Integer> that_line : data){
    Row row = RowFactory.create(that_line.toArray());
    rows.add(row);
}

// Then just make the dataframe! (no instead of using RDD, use the List<Row>
Dataset<Row> r2DF = sparkSession.createDataFrame(rows, schema); // supposing you have schema already.
r2DF.show();

From this post: https://stackoverflow.com/questions/47262422/how-to-convert-java-arraylist-to-apache-spark-dataset