帮我优化以下代码并解释为什么这么修改： public AjaxResult importDataMultipartFile file boolean updateSupport throws Exception Workbook workbook = null; InputStream inputStream = filegetInputStream;

修改后的代码如下：

public AjaxResult importData(MultipartFile file, boolean updateSupport) throws Exception { Workbook workbook = null; InputStream inputStream = file.getInputStream(); String fileExtension = getFileExtension(Objects.requireNonNull(file.getOriginalFilename())); // 根据文件类型进行区分 if (fileExtension.equals("xlsx")) { workbook = new XSSFWorkbook(inputStream); } else if (fileExtension.equals("xls")) { workbook = new HSSFWorkbook(inputStream); }

String sheetName = "a-HKG BW WHSE-in bound"; // 导入信息的工作表名称
Sheet sheet = workbook.getSheet(sheetName);
if (sheet == null) {
    throw new IllegalArgumentException("Sheet with name " + sheetName + " does not exist");
}
InputStream getSheetInputStream = workbookToInputStream(workbook);
ExcelUtil<AHkgBwWhseInBound> util = new ExcelUtil<>(AHkgBwWhseInBound.class);
List<AHkgBwWhseInBound> dataManagementList = util.importExcel(getSheetInputStream, 1);
String operName = ShiroUtils.getSysUser().getLoginName();
String message = aHkgBwWhseInBoundService.importData(dataManagementList, updateSupport, operName);
return AjaxResult.success(message);

}

private static String getFileExtension(String fileName) { int dotIndex = fileName.lastIndexOf("."); if (dotIndex != -1 && dotIndex != 0) { return fileName.substring(dotIndex + 1); } else { return ""; } }

private static InputStream workbookToInputStream(Workbook workbook) throws IOException { ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream(); workbook.write(byteArrayOutputStream); return new ByteArrayInputStream(byteArrayOutputStream.toByteArray()); }

修改解释：

1. 简化了获取文件扩展名的逻辑，使用了更直观的方式。
2. 移除了对空指针的判断，使用了Objects.requireNonNull确保file.getOriginalFilename()不为null。
3. 删除了对workbook是否为null的判断，因为如果文件类型不支持，workbook会为null，后续的操作会抛出异常。
4. 简化了获取sheet的逻辑，直接使用workbook.getSheet(sheetName)获取指定名称的sheet。
5. 在workbookToInputStream方法中，直接返回创建的ByteArrayInputStream对象，省去了关闭ByteArrayOutputStream的步骤