Question 224118 in Flutter Question posted in
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Unable to parse Json in Flutter

I used to parse JSON to list of objects by the following way:

final response = await api(map);
var raw = jsonDecode(response.body)[0];
dataList = parseJson(raw["datalist"]);

List<dataRecord> parseJson(String responseBody) {
    final parsed = convert.jsonDecode(responseBody).cast<Map<String, dynamic>>();
    return parsed.map<dataRecord>((json) => dataRecord.fromJson(json)).toList();
  }

and the JSON is in this format:

datalist: [{"id": 29737, "rent": 700, "unit": "A", .....

this works fine in all of my existing projects.

However, I am now retrieving data from an external source and the JSON is in this format:

data: [{id: 4109486, unicorn_id: 7836045, memorial_id: 23072601320076, ...

field labels and string values all without quotes, and I am not able to use the same parseJson function to parse the JSON.

Tags:

2

Answers


  1. 0

    Use this method to add quotes around the keys and string values in the response.

    String preprocessResponse(String responseBody) {
  final processedResponse = responseBody.replaceAllMapped(
    RegExp(r'(w+):'),
    (match) => '"${match.group(1)}":',
  );

  return '{"datalist": [$processedResponse]}';
}
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  2. 0

    One possible way is to add a hook to the JSON parser.
    First hook to parse _keyValue.
    The second hook is to parse _string.

    This allows you to parse regular JSON and JSON that uses identifiers as object keys.

    import 'package:parser_combinator/extra/json_parser.dart' as json_parser;
import 'package:parser_combinator/parser/predicate.dart';
import 'package:parser_combinator/parser/recognize.dart';
import 'package:parser_combinator/parser/skip_while.dart';
import 'package:parser_combinator/parser/skip_while1.dart';
import 'package:parser_combinator/parser_combinator.dart';
import 'package:parser_combinator/parsing.dart';
import 'package:parser_combinator/runtime.dart';
import 'package:parser_combinator/tracing.dart';

void main(List<String> args) {
  const raw1 = '''
data: [{id: 4109486, unicorn_id: 7836045, memorial_id: 23072601320076}]
    ''';

  const raw2 = '''
"data": [{"id": 4109486, "unicorn_id": 7836045, "memorial_id": 23072601320076}]
    ''';

  final input1 = '{$raw1}';
  final r1 = _parse(input1);
  print(r1);

  final input2 = '{$raw2}';
  final r2 = _parse(input2);
  print(r2);
}

bool _isAllowedChar(int c) => c == 0x5f;

bool _isIdentEnd(int c) => _isIdentStart(c) || isDigit(c);

bool _isIdentStart(int c) => isAlpha(c) || _isAllowedChar(c);

Object? _parse(String input) {
  const ident = Recognize2(SkipWhile1(_isIdentStart), SkipWhile(_isIdentEnd));

  var stringCount = 0;
  Result<O>? parse<O>(Parser<String, O> parser, State<String> state) {
    final name = parser.name;
    if (name == '_keyValue') {
      stringCount = 0;
    }

    final result = parser.parse(state);
    if (name == '_string') {
      stringCount++;
      if (result == null && stringCount == 1) {
        final result2 = ident.parse(state);
        if (result2 != null) {
          return result2 as Result<O>;
        }
      }
    }

    return result;
  }

  bool fastParse<O>(Parser<String, O> parser, State<String> state) {
    return parser.parse(state) != null;
  }

  final builder = TracerBuilder(
      fastParse: fastParse,
      parse: parse,
      filter: <O>(parser) {
        return parser.name == '_keyValue' || parser.name == '_string';
      });
  final p = builder.build(json_parser.parser);
  return parseString(p.parse, input);
}

    Output:

    {data: [{id: 4109486, unicorn_id: 7836045, memorial_id: 23072601320076}]}
{data: [{id: 4109486, unicorn_id: 7836045, memorial_id: 23072601320076}]}
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