POI reads and writes Excel table data

POI is an open source library for reading and writing Microsoft Office documents under Apache, including but not limited to: Word, Excel, PowerPoint, Visio. Official statement: Starting from version 4.0.1, using this library requires jdk1.8 or higher version support. The latest version used in this article is: 4.1.2.
This article only uses the function of reading and writing excel table data of this library, and it is a table file with xlsx extension.

private void onOk() {
  String filePath = "E:/setup/test.xlsx";
  LinkedList<XSSFRow> list = new LinkedList<XSSFRow>();
  try {
    // 读取表格中第一个sheet的数据
    readExcel(list, filePath);
    // 将上述读取的数据写入第二个sheet中
    writeExcel(list, filePath);
  } catch (Exception x) {
    x.printStackTrace();
  }
}

private void readExcel(LinkedList<XSSFRow> list, String filePath) throws Exception {
  FileInputStream inputStream = new FileInputStream(filePath);
  XSSFWorkbook workbook = new XSSFWorkbook(inputStream);
  XSSFSheet sheet = workbook.getSheetAt(0); // 获取表格中第一个sheet
  int firstRowNum = sheet.getFirstRowNum(); // 获取sheet中第一行的序号
  int lastRowNum = sheet.getLastRowNum(); // 获取sheet中最后一行的序号
  for (int i = firstRowNum; i <= lastRowNum; i++) {
    XSSFRow row = sheet.getRow(i);
    if (row == null) {
      break;
    }
    int first = row.getFirstCellNum(); // 获取当前行中第一个单元格的序号
    int last = row.getLastCellNum(); // 获取当前行中最后一个单元格的序号
    if (first < 0 || last < 0) {
      break;
    }
    for (int j = first; j < last; j++) {
      XSSFCell cell = row.getCell(j);
      CellType cellType = cell.getCellType();
      if (cellType == CellType.STRING) {
        String value = cell.getStringCellValue();
        System.out.println("STRING value=" + value);
      } else if (cellType == CellType.NUMERIC) {
        String value = cell.getNumericCellValue();
        System.out.println("NUMERIC value=" + value);
      }
    }
    list.add(row);
  }
  inputStream.close();
}

private void writeExcel(LinkedList<XSSFRow> list, String filePath) throws Exception {
  XSSFWorkbook workbook = new XSSFWorkbook(new FileInputStream(filePath));
  int count = workbook.getNumberOfSheets(); // 获取表格中sheet的数量
  XSSFSheet sheet = null;
  if (count > 1) {
    sheet = workbook.getSheetAt(1);
  } else {
    sheet = workbook.createSheet();
  }
  XSSFRow row;
  XSSFCell cell;
  //把List里面的数据写到excel中
  for (int i = 0; i < list.size(); i++) {
    // 创建行
    row = sheet.createRow(i);
    XSSFRow tempRow = list.get(i);
    for (int j = tempRow.getFirstCellNum(); j < tempRow.getLastCellNum(); j++) {
      cell = row.createCell(j); // 创建单元格
      XSSFCell tempCell = tempRow.getCell(j);
      switch (tempCell.getCellType()) {
        case NUMERIC:
          if (DateUtil.isCellDateFormatted(tempCell)) { // 时间格式的单元格，需要特殊处理
            Date date = tempCell.getDateCellValue();
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd");
            cell.setCellValue(sdf.format(date)); // 设置单元格内容
          } else {
            cell.setCellValue(tempCell.getNumericCellValue()); // 设置单元格内容
          }
          break;
        case STRING:
          cell.setCellValue(tempCell.getStringCellValue()); // 设置单元格内容
          break;
      }
    }
  }
  //用输出流写到excel
  FileOutputStream outputStream = new FileOutputStream(filePath);
  workbook.write(outputStream);
  outputStream.flush();
  outputStream.close();
}