无法将数据写入Excel文件单元格

Question

I want to write a String into an existing Excel file cell using Java and apache library poi. Here is my method:

public void setSuccessMessageInExcellFile(File uploadFile, HttpServletResponse response) {          

    try {
        FileInputStream fileInputStream = new FileInputStream(uploadFile);

        HSSFWorkbook workbook = new HSSFWorkbook(fileInputStream);
        HSSFSheet excelSheet = workbook.getSheetAt(0); 
        HSSFCell cell = excelSheet.getRow(0).getCell(0);
        cell.setCellValue("Imported");

        fileInputStream.close();
        FileOutputStream out = new FileOutputStream(uploadFile);
        workbook.write(out);
        out.close();
    } catch(Exception ex) {
        ex.getCause().printStackTrace();
    }           
}

there is no error but "Imported" text is not available in my Excel file.

Answer 1

Be sure that your file exists, writable and has the right Excel version. After that you should change your code like that, because you are getting a NullPointerException otherwise:

public void setSuccessMessageInExcellFile(File uploadFile, HttpServletResponse response) {


    try {
        FileInputStream fileInputStream = new FileInputStream(uploadFile);

        HSSFWorkbook workbook = new HSSFWorkbook(fileInputStream);
        HSSFSheet excelSheet = workbook.getSheetAt(0); 
        HSSFCell cell = excelSheet.createRow(0).createCell(0);
        cell.setCellValue("Imported");

        fileInputStream.close();
        FileOutputStream out = new FileOutputStream(uploadFile);
        workbook.write(out);
        out.close();
    } catch(Exception ex) {
        ex.getCause().printStackTrace();
    } 
}

And better would be putting the closables in the try as argument like that:

try(FileInputStream fileInputStream = new FileInputStream(uploadFile);
            HSSFWorkbook workbook = new HSSFWorkbook(fileInputStream); 
            FileOutputStream out = new FileOutputStream(uploadFile)) {            
        HSSFSheet excelSheet = workbook.getSheetAt(0); 
        HSSFCell cell = excelSheet.createRow(0).createCell(0);
        cell.setCellValue("Imported"); 
        workbook.write(out);         
    } catch(Exception ex) {
        ex.getCause().printStackTrace();
    }