Save to excel file leads to java.lang.NullPointerException

Question

I try to save my data to a excel file. I created the excel file to add titles etc and

private void saveFile(HttpSession session, ActionsDB actions){

    ArrayList<Record> records = (ArrayList<Record>) (session.getAttribute("records"));
    System.out.println("recordds "+ records.toString());

    Row row;
    Cell column;
    int size = records.size();

    System.out.println("size is "+ size);
    String s1="",s2="",s3="",s4= "", s="";

    try {
            //Get the excel file.
            FileInputStream file = new FileInputStream(new File("C:\\work\\test.xls"));
            //Get workbook for XLS file.
            HSSFWorkbook workbook = new HSSFWorkbook(file);
            //Get first sheet from the workbook.
            //If there have >1 sheet in your workbook, you can change it here IF you want to edit other sheets.
            HSSFSheet sheet1 = workbook.getSheetAt(0);


            for(int i=0; i<size; i++){
                 System.out.println("i: " +i);
                 row = sheet1.getRow(i+1);                     
                 column = row.getCell(0);

                 column.setCellValue(records.get(i).getDate()); // insert date

                 column = row.getCell(1);
                 column.setCellValue(records.get(i).getTime()); //insert shift

                 column = row.getCell(2);
                 column.setCellValue(records.get(i).getShift());

                 column = row.getCell(3);
                 column.setCellValue(records.get(i).getIdMachine());

                 column = row.getCell(4);
                 column.setCellValue(records.get(i).getKaloupi());

                 column = row.getCell(5);
                 column.setCellValue(records.get(i).isStardEnd());

                 column = row.getCell(6);
                 column.setCellValue(records.get(i).hasLabel());

                 column = row.getCell(7);
                 column.setCellValue(records.get(i).getTimeCycle());

                 column = row.getCell(8);
                 column.setCellValue(records.get(i).getId());
            }

            file.close();
            System.out.println("10");
            File desktopDir = new File(System.getProperty("user.home"), "Desktop");
            System.out.println(desktopDir.getPath() + " " + desktopDir.exists());
            String pathToDesktop = desktopDir.getPath()+ "\\workPlanner\\print";
            System.out.println(pathToDesktop);

            createFolderToDesktop(pathToDesktop); 

            FileOutputStream out =  new FileOutputStream(new File(pathToDesktop,  "machinesRecords.xls"));

            workbook.write(out);
            out.close();

        } catch (FileNotFoundException e) {
            e.printStackTrace();
            System.out.println("1111111111");

        } catch (IOException e) {
            e.printStackTrace();
            System.out.println("2222222");                               
        }

}              

In the cosole

recorddssss [the eleements are printed fine]
sizee is 38
i: 0
Exceptionn: java.lang.NullPointerException

After many hours thinking where this exception comes from (as I have done the same thing in an other method with a diferrrent file and it works there fine), I replaced the excel file with that one and then works fine. I dont understand why with the new file doesn't work and with an old one is working.. I checked the properties both of the files and they have the same security properties

Answer 1

After many days, I found what was causing the null exception. The problem was when the row was null ... with the following

row = sheet1.getRow(i+1); 
if(row == null){
  row = sheet1.createRow(i+1);
}

the program run well.