Dart从不可编辑的大文件中读取JSON对象 [英] Dart read json objects from Uneditable large file

问题描述

我有一个无法编辑的大文件，并且其中还有更多 jsonObject ，例如：

i have a large file which that uneditable and i have more jsonObject into that, for example:

{"id":"@123456","v":"1"}

这不是 jsonArray 我无法解析和读取它，例如：

this isn't jsonArray which i can't parse and read it, for example:

String file= new File('file.json').readAsStringSync();
Map<String, dynamic> data = json.decode(file);

您认为我该如何从文件中读取此对象并显示键和值？

you think how can i read this objects from file and show key and values?

推荐答案

尝试以下解决方案。我最终为您的输入格式创建了一个解析器，该解析器将返回Stream中每个解析的JSON对象。

Try the following solution. I ended up making a parser for your input format which are returning each parsed JSON object in a Stream.

如果您的JSON中的任何字符串包含<$，解析器将无法工作。 c $ c> {或} 。如果是这种情况，我可以扩展解析器，以便将其考虑在内，但我不想使其超出必要的高度。

The parser will not work if any strings in your JSON contains { or }. If that is the case, I can expand the parser so it takes this into account but I don't want to make it more advanced than necessary.

import 'dart:async';
import 'dart:convert';
import 'dart:io';

Future<void> main() async {
  final ids = await File('large_file.json')
      .openRead()
      .transform(const Utf8Decoder())
      .transform<dynamic>(JsonObjectTransformer())
      .map((dynamic json) => json['id'] as String)
      .toList();

  print(ids); // [@123456, @123456]
}

class JsonObjectTransformer extends StreamTransformerBase<String, dynamic> {
  static final _openingBracketChar = '{'.codeUnitAt(0);
  static final _closingBracketChar = '}'.codeUnitAt(0);

  @override
  Stream<dynamic> bind(Stream<String> stream) async* {
    final sb = StringBuffer();
    var bracketsCount = 0;

    await for (final string in stream) {
      for (var i = 0; i < string.length; i++) {
        final current = string.codeUnitAt(i);
        sb.writeCharCode(current);

        if (current == _openingBracketChar) {
          bracketsCount++;
        }

        if (current == _closingBracketChar && --bracketsCount == 0) {
          yield json.decode(sb.toString());
          sb.clear();
        }
      }
    }
  }
}

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