Question

I am new to Java POI and i am trying to overwrite an excel file using Java POI.Let me make it clear, i don’t want to open a new .xls file every time time i build the code however the code i wrote does it that way.The purpose for this is to, i will build the chart on excel and read the values for the chart from the database and write it to the excel file by using Java POI.Here is my code:

HSSFWorkbook workbook = new HSSFWorkbook();
HSSFSheet firstSheet = workbook.createSheet("oldu");
HSSFSheet secondSheet = workbook.createSheet("oldu2");

HSSFRow rowA = firstSheet.createRow(6);
HSSFCell cellA = rowA.createCell(3);
cellA.setCellValue(new HSSFRichTextString("100"));
cellA.setCellValue(100);

HSSFRow rowB = secondSheet.createRow(0);
HSSFCell cellB = rowB.createCell(0);
cellB.setCellValue(new HSSFRichTextString("200"));

FileOutputStream fos = null;
try {
    fos = new FileOutputStream(new File("CreateExcelDemo.xls"));
    workbook.write(fos);
} catch (IOException e) {
    e.printStackTrace();
} finally {
    if (fos != null) {
        try {
            fos.flush();
            fos.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Answer 1

Always use the same filename and when you run the program it will overwrite the file.

EDIT
If you want to modify an existing excel file then have a look HERE and scroll down to the section on “Reading or Modifying an existing file”.