Flutter -如何将嵌套的json解析为带有泛型的类？

import 'dart:convert';

class User {
  final int id;
  final String name;
  final List<Post> posts;

  User({required this.id, required this.name, required this.posts});

  factory User.fromJson(Map<String, dynamic> json) {
    var postsList = json['posts'] as List;
    List<Post> posts = postsList.map((post) => Post.fromJson(post)).toList();

    return User(
      id: json['id'],
      name: json['name'],
      posts: posts,
    );
  }
}

class Post {
  final int id;
  final String title;
  final String body;

  Post({required this.id, required this.title, required this.body});

  factory Post.fromJson(Map<String, dynamic> json) {
    return Post(
      id: json['id'],
      title: json['title'],
      body: json['body'],
    );
  }
}

void main() {
  String jsonString = '''
    {
      "id": 1,
      "name": "John Doe",
      "posts": [
        {
          "id": 1,
          "title": "Hello",
          "body": "Lorem ipsum"
        },
        {
          "id": 2,
          "title": "World",
          "body": "Dolor sit amet"
        }
      ]
    }
  ''';

  Map<String, dynamic> json = jsonDecode(jsonString);
  User user = User.fromJson(json);

  print('User ID: ${user.id}');
  print('User Name: ${user.name}');
  print('User Posts:');
  user.posts.forEach((post) {
    print('  Post ID: ${post.id}');
    print('  Post Title: ${post.title}');
    print('  Post Body: ${post.body}');
  });
}