Fast edit of Excel file

I have this code to edit certain cells in my Excel file using Apache POI, but it is really slow. How can I improved the performance?

Ideally I would like to edit 20000 rows in less than one minute. At the moment it does ~100/min. Any suggestions would be great.

public static void main(String[] args) throws IOException, InvalidFormatException{
        InputStream inp = new FileInputStream("test.xls");
        FileOutputStream fileOut = new FileOutputStream("edited-test.xls");
        Workbook wb = WorkbookFactory.create(inp);
        Sheet sheet = wb.getSheetAt(0);
        for(int i=2;i <20002;i++){
            Row row = sheet.getRow(i);

            Cell cell4 = row.getCell(4); 
            cell4.setCellValue(i); 

            Cell cell6 = row.getCell(6);
            cell6.setCellValue("aa"+i); 

            Cell cell8 = row.getCell(8); 
            cell8.setCellValue("2"); 

            wb.write(fileOut);
            System.out.println(i);
        }
        fileOut.close();
        System.out.println("Done!");
    }

First thing you should do is only write the file out once, not 20,000 times ;-)

Move the wb.write(fileOut); to be outside the loop.....

Additionally, there may be some improvement by reversing the loop:

for(int i=2;i <20002;i++){

can become:

for(int i=20001;i >= 2;i--){

This may make some memory management in the API faster.

StackExchange Code Review Q#41656, answer score: 8