using apache poi to parse a particular column and print required string in an adjacent column

Question

I am trying to print a string in a specific column of a xlsx file using apache poi in java. I have parsed the column x using regex and printing the required string in column y. However the getRowNum() of the code flags ConcurrentModificationExceptio. Below is the code snippet. Please help

|Column X|Column Y|

|Barath  |Bar     |         //Regex Matches Bar and prints it in Column y (Required output).


while (rows.hasNext())
    {
        row=(XSSFRow) rows.next();
        Iterator cells = row.cellIterator();
        while (cells.hasNext())
        {
            cell=(XSSFCell) cells.next();
            if (cell.getCellType() == XSSFCell.CELL_TYPE_STRING)
            {
                Matcher m = p.matcher(cell.getRichStringCellValue().getString());
                //rownr = row.getRowNum();
                if(m.find()){

                    sheet.createRow(row.getRowNum()).createCell(colnr+6).setCellValue(row.getCell(colnr+4).toString().substring(m.start(),m.end()-1).replace(":", ""));                     //row.getRowNum() function causes Concurrent modification exception  colnr+6 is destination column and Colnr+4 is column to be parsed.
                    System.out.print(row.getCell(colnr+4).toString().substring(m.start(),m.end()-1).replace(":", "")+"\n");          //Prints the parsed string in the console correctly
                }                   
            }
        }
    }

Answer 1

It seems that, when you are creating a row, the original rows collection is modified, while you are iterating over it. Hence the ConcurrentModificationException.

There are a few ways to fix this, but in this case, I don't think you need to create the row at all, since the row already exists. So instead of...

sheet.createRow(...).createCell(colnr+6)

...you would have:

row.createCell(colnr+6)