Java如何实现按行分割大文件

public static List<File> splitDataToSaveFile(int rows, File sourceFile, String targetDirectoryPath) {
  long startTime = System.currentTimeMillis();
  List<File> fileList = new ArrayList<>();
  log.info("开始分割文件");
  File targetFile = new File(targetDirectoryPath);
  if (!sourceFile.exists() || rows <= 0 || sourceFile.isDirectory()) {
   return null;
  }
  if (targetFile.exists()) {
   if (!targetFile.isDirectory()) {
    return null;
   }
  } else {
   targetFile.mkdirs();
  }
 
  try (FileInputStream fileInputStream = new FileInputStream(sourceFile);
    InputStreamReader inputStreamReader = new InputStreamReader(fileInputStream, StandardCharsets.UTF_8);
    BufferedReader bufferedReader = new BufferedReader(inputStreamReader)) {
   StringBuilder stringBuilder = new StringBuilder();
   String lineStr;
   int lineNo = 1, fileNum = 1;
   while ((lineStr = bufferedReader.readLine()) != null) {
    stringBuilder.append(lineStr).append("\r\n");
    if (lineNo % rows == 0) {
     File file = new File(targetDirectoryPath + File.separator + fileNum + sourceFile.getName());
     writeFile(stringBuilder.toString(), file);
     //清空文本
     stringBuilder.delete(0, stringBuilder.length());
     fileNum++;
     fileList.add(file);
    }
    lineNo++;
   }
   if ((lineNo - 1) % rows != 0) {
    File file = new File(targetDirectoryPath + File.separator + fileNum + sourceFile.getName());
    writeFile(stringBuilder.toString(), file);
    fileList.add(file);
   }
   long endTime = System.currentTimeMillis();
   log.info("分割文件结束，耗时：{}秒", (endTime - startTime) / 1000);
  } catch (Exception e) {
   log.error("分割文件异常", e);
  }
  return fileList;
 }
 
 private static void writeFile(String text, File file) {
  try (
    FileOutputStream fileOutputStream = new FileOutputStream(file);
    OutputStreamWriter outputStreamWriter = new OutputStreamWriter(fileOutputStream, StandardCharsets.UTF_8);
    BufferedWriter bufferedWriter = new BufferedWriter(outputStreamWriter, 1024)
  ) {
   bufferedWriter.write(text);
  } catch (IOException e) {
   e.printStackTrace();
  }
 }