Edit existing excel files using jxl api / Apache POI

The tutorials here are very helpful and well-written. They use an external JAR developed by the Apache POI project.
Here’s an simple example of editing one cell:

    InputStream inp = new FileInputStream("wb.xls");
    Workbook wb = WorkbookFactory.create(inp);
    Sheet sheet = wb.getSheetAt([sheet index]);
    Row row = sheet.getRow([row index]);
    Cell cell = row.getCell([cell index]);
    String cellContents = cell.getStringCellValue(); 
    //Modify the cellContents here
    // Write the output to a file
    cell.setCellValue(cellContents); 
    FileOutputStream fileOut = new FileOutputStream("wb.xls");
    wb.write(fileOut);
    fileOut.close();

Hope it helps