我有办法
我做了下面的函数将文件分割成多个部分。

Future<List<File>> splitFileInSegment(File file,
      {int chunkSize = 1800,
      required String cachePath,
      required String fileName}) async {
    int sizeOfFile = chunkSize * 1024;
    ByteData bd = await rootBundle.load(file.path);
    List<int> bytes = bd.buffer.asUint8List();
    List<List<int>> splitBytes = [];
    int isHalfFileNeeded = bytes.length % sizeOfFile;
    int numberOfFiles = bytes.length ~/ sizeOfFile;
    if (isHalfFileNeeded > 0) {
      numberOfFiles = numberOfFiles + 1;
    }
    int offset = 0;
    for (int i = 0; i < numberOfFiles; i++) {
      int getLastIndex = 0;
      int bytesReached = (i + 1) * sizeOfFile;
      if (bytesReached <= bytes.length) {
        getLastIndex = bytesReached;
      } else {
        getLastIndex = offset + isHalfFileNeeded;
      }
      List<int> byteList = bytes.sublist(offset, getLastIndex);
      splitBytes.add(byteList);
      offset += sizeOfFile;
    }
    List<File> files = [];
    for (int index = 0; index < splitBytes.length; index++) {
      final File tempFile = File("$cachePath/$fileName" + "_" + "$index.json");
      File file = await tempFile.writeAsBytes(splitBytes[index]);
      files.add(file);
    }
    return files;
  }

字符集

import 'dart:io';
void main() {
  File originalFile = File('file_name.tar.gz');
  List<int> bytes = originalFile.readAsBytesSync();
  int chunkSize = 1800 * 1024; // 1800 KB
  int numOfFiles = (bytes.length / chunkSize).ceil();
  for (int i = 0; i < numOfFiles; i++) {
    int start = i * chunkSize;
    int end = (i + 1) * chunkSize;
    if (end > bytes.length) {
      end = bytes.length;
    }
    List<int> chunk = bytes.sublist(start, end);
    File newFile = File('file_name_${i + 1}.json');
    newFile.writeAsBytesSync(chunk);
  }
  print('File split into $numOfFiles JSON files.');
}

字符集