How to fix the width of the columns in a table that is within the cell of another table with apache poi and Java?

I am parsing a XML that has HTML tags in it. After parsing the XML I am trying to create a table that is within the cell of another table and create a word document with these contents. I implemented the table within a table with the help of the answer of this Question. However, I am unable to set the width of the columns of the nested table. When the word document is generated the generated nested table is so ugly with super narrow columns that has to be manually adjusted to have a desired column width. I would like to set some default values as the desired column width. The generated word document with the nested table has been provided in the picture. I am using the following code to set the column width but no luck so far.

  for (int i = 0; i < nestedtable.getNumberOfRows(); i++) {
  XWPFTableRow row = nestedtable.getRow(i);
  int numCells = row.getTableCells().size();
  for (int j = 0; j < numCells; j++) {
    XWPFTableCell cell = row.getCell(j);
    CTTblWidth cellWidth = cell.getCTTc().addNewTcPr().addNewTcW();
    CTTcPr pr = cell.getCTTc().addNewTcPr();
    pr.addNewNoWrap();
    cellWidth.setW(BigInteger.valueOf(400));
  }
}

How should I get out of this problem? The generated word document is looking so ugly due to this nested table structure.

The question you linked was about how to insert a table into a table cell in a Word-table using Apache POI. Nothing about how to set column widths. And, since it is from 2017, it answers this using Apache POI versions of 2017. But Apache POI is highly in development. So current versions will have more straightforward methods to do things.

Especially to set widths of XWPFTable and/or XWPFTableCell, current Apache POI version 5.2.3 provides setWidth methods in XWPFTable as well as in XWPFTableCell. The most straightforward is public void setWidth(java.lang.String widthValue). There the String widthValue may be the width to the value "auto", an integer value (20ths of a point), or a percentage ("nn.nn%").

Also setting borders is much more straightforward now as there are XWPFTable.set*Border methods now.

So the code should look like so now using current Apache POI.

import java.io.*;
import org.apache.poi.xwpf.usermodel.*;
public class CreateWordTableInTable {
static void setAllBorders(XWPFTable table, XWPFTable.XWPFBorderType borderType, int size, int space, java.lang.String rgbColor) {
table.setTopBorder(borderType, size, space, rgbColor);
table.setRightBorder(borderType, size, space, rgbColor);
table.setBottomBorder(borderType, size, space, rgbColor);
table.setLeftBorder(borderType, size, space, rgbColor);
table.setInsideHBorder(borderType, size, space, rgbColor);
table.setInsideVBorder(borderType, size, space, rgbColor);	 
}
public static void main(String[] args) throws Exception {
XWPFDocument document = new XWPFDocument();
XWPFTable tableOne = document.createTable(2,2);
tableOne.setWidth("100%");
XWPFTableRow tablerow = tableOne.getRow(0);
tablerow.getCell(0).setWidth("40%");
tablerow.getCell(1).setWidth("60%");
tablerow.getCell(0).setText("Test");
tablerow.getCell(1).setText("Test");
tablerow = tableOne.getRow(1);
tablerow.getCell(0).setText("Test");
XWPFParagraph paragraph = tablerow.getCell(1).getParagraphArray(0);
XWPFTable tableTwo = tablerow.getCell(1).insertNewTbl(paragraph.getCTP().newCursor());
tableTwo.setWidth(0); // This is necessary because a XWPFTable created by insertNewTbl seems not to have full internally structure. It lacks the cell width field in this case.
tableTwo.setWidth("100%");
setAllBorders(tableTwo, XWPFTable.XWPFBorderType.SINGLE, 4, 0, "000000");
tablerow = tableTwo.createRow();
tablerow.createCell().setText("aaaaaaaaaa");
tablerow.createCell().setText("jjjjjjjj"); 
tablerow = tableTwo.createRow(); 
tablerow.getCell(0).setText("bbbbbbbbbb"); 
tablerow.getCell(1).setText("gggggggggg");
try (FileOutputStream out = new FileOutputStream("./CreateWordTableInTable.docx")) {
document.write(out);
}
document.close();
}
}

Note: A XWPFTable created by insertNewTbl seems not to have full internally structure. It has no default border setting for example and it lacks the internally cell width field. That's why explicit border setting is necessary. And calling setWidth(int width) is necessary before calling setWidth(java.lang.String widthValue) as the first sets the internally cell width field while the second relies on the presence of that field and fails if it is not present.

Result looks like so for me: