Python requests请求转Flutter时提示ParamList不存在如何解决

使用Python编写的requests请求代码可正常运行，调用目标接口后可得到上述截图所示的正常响应。
现需要将该请求逻辑迁移至Flutter端实现，首次编写的Dart请求代码如下：

import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'package:html/parser.dart';
import 'package:dio/dio.dart';
void main() async {
  var url = 'https://www.lottecinema.co.kr/LCWS/Ticketing/TicketingData.aspx';

  var dic = {
    "paramList": {
      "MethodName": "GetPlaySequence",
      "channelType": "HO",
      "osType": "W",
      "osVersion":
          "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/102.0.0.0 Safari/537.36",
      "playDate": "2022-06-29",
      "cinemaID": "1|0001|1013",
      "representationMovieCode": ""
    }
  };

  var req = await Dio().post(
    '$url',
    data: dic,
  );
  print(req);


  runApp(const MyApp());
}

运行上述代码后接口返回韩文错误ParamList가 존재하지 않습니다，对应含义为ParamList does not exist.（ParamList参数不存在），报错截图如下：

之后尝试第二种实现方案，代码如下：

import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'package:html/parser.dart';
import 'package:dio/dio.dart';

void main() async {
  var url = 'https://www.lottecinema.co.kr/LCWS/Ticketing/TicketingData.aspx';

  var dic = {
    "paramList": {
      "MethodName": "GetPlaySequence",
      "channelType": "HO",
      "osType": "W",
      "osVersion":
          "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/102.0.0.0 Safari/537.36",
      "playDate": "2022-06-29",
      "cinemaID": "1|0001|1013",
      "representationMovieCode": ""
    }.toString()
  };

  var request = await http.MultipartRequest('Post', Uri.parse('$url'));
  request.fields.addAll(dic);

  http.StreamedResponse response = await request.send();
  var responseString = await response.stream.bytesToString();

  print("STATUS CODE : ${response.statusCode}");
  print("RESPONSE BODY : ${responseString}");

  runApp(const MyApp());
}

该版本代码依然无法得到正确的接口响应，运行结果截图如下：

接口要求的paramList参数格式、预期响应结果参考如下截图：

报错核心原因是请求参数格式和Python requests默认发送的表单格式不匹配。该.NET接口要求paramList字段的值是标准JSON序列化后的字符串，且请求要使用application/x-www-form-urlencoded格式提交，不能直接传嵌套Map，也不能用Dart默认的Map toString()方法——Dart的Map toString()输出的是{key: value}格式，不是标准JSON结构。

可直接运行的Dio实现代码 #

import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:dio/dio.dart';

void main() async {
  var url = 'https://www.lottecinema.co.kr/LCWS/Ticketing/TicketingData.aspx';

  // 内层参数先序列化为标准JSON字符串，作为paramList的字段值
  var formData = {
    "paramList": jsonEncode({
      "MethodName": "GetPlaySequence",
      "channelType": "HO",
      "osType": "W",
      "osVersion":
          "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/102.0.0.0 Safari/537.36",
      "playDate": "2022-06-29",
      "cinemaID": "1|0001|1013",
      "representationMovieCode": ""
    })
  };

  var req = await Dio().post(
    url,
    data: formData,
    options: Options(
      contentType: Headers.formUrlEncodedContentType,
      headers: {
        "User-Agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/102.0.0.0 Safari/537.36"
      }
    ),
  );
  print(req.data);

  runApp(const MyApp());
}

关键调整点 #

• 不要直接传嵌套Map给请求体：Dio默认会把嵌套Map序列化为多层结构，而接口只接收一级表单字段paramList，其值为JSON字符串
• 禁止用Dart的Map.toString()生成JSON：该方法输出格式不符合JSON规范，必须使用dart:convert包的jsonEncode()方法做标准序列化
• 明确指定contentType为application/x-www-form-urlencoded，和Python requests提交表单的默认格式保持一致
• 额外在请求头添加User-Agent模拟浏览器请求，避免被接口反爬策略拦截

内容的提问来源于stack exchange，提问作者jhlee