使用 Dart 调用 REST API

JSON : Placeholder

JSON : Placeholder (https://jsonplaceholder.typicode.com/) 是一个用于测试的 REST API 网站。
以下使用 Dart 调用该网站的 REST API，获取字符串以及 JSON 数据。

• GET /posts/1
• GET /posts
• POST /posts
• PUT /posts/1
• DELETE /posts/1

所有 GET API 都返回JSON数据，格式（JSON-Schema）如下：

{
  "type":"object",
  "properties": {
    "userId": {"type" : "integer"},
    "id": {"type" : "integer"},
    "title": {"type" : "string"},
    "body": {"type" : "string"}
  }
}

创建工程

打开 Intellij IDEA， 安装 Dart 插件
新建工程，选择 Dart -> Dart Command Line App, 输入 Dart SDK 路径，
然后点击 Next，输入工程名 example，完成向导。

添加依赖

在 pubspec.yaml 的 dependencies 部分添加依赖

dependencies:
  json_annotation: ^3.0.0
  analyzer: '0.39.14'
  http: 0.12.2

点击文件上方的 Pub get 链接下载依赖

Dart

example.dart 代码如下

import 'dart:convert';

import 'package:json_annotation/json_annotation.dart';

part 'example.g.dart';

@JsonSerializable()
class Post {
  int userId;
  int id;
  String title;
  String body;

  Post() {}
  factory Post.fromJson(Map<String, dynamic> json) => _$PostFromJson(json);
  Map<String, dynamic> toJson() => _$PostToJson(this);
  @override
  String toString() => 'Post {userId = $userId, id = $id, title = "$title", body = "${body?.replaceAll("
", r"
")}"}';
}

String baseUrl = 'http://jsonplaceholder.typicode.com/';

Future<String> getPostAsString() async {
  final response = await http.get("${baseUrl}posts/1");
  return response.body;
}

Future<Post> getPostAsJson() async {
  final response = await http.get("${baseUrl}posts/1");
  return Post.fromJson(json.decode(response.body));
}

Future<List<Post>> getPosts() async {
  final response = await http.get("${baseUrl}posts");
  final j = json.decode(response.body);
  return (j as List).map((e) => Post.fromJson(e)).take(2).toList();
}

Future<String> createPost() async {
  final o = Post()
    ..id = 0
    ..userId = 1
    ..title = 'test title'
    ..body = 'test body';
  final response = await http.post("${baseUrl}posts", body: json.encode(o));
  return response.body;
}

Future<String> updatePost() async {
  final o = Post()
    ..id = 1
    ..userId = 1
    ..title = 'test title'
    ..body = 'test body';
  final response = await http.put("${baseUrl}posts/1", body: json.encode(o));
  return response.body;
}

Future<String> deletePost() async {
  final response = await http.delete("${baseUrl}posts/1");
  return response.body;
}

Future httpTest() async {
  print(await getPostAsString());
  print(await getPostAsJson());
  print(await getPosts());
  print(await createPost());
  print(await updatePost());
  print(await deletePost());
}

void main() {
  httpTest();
}

• getPostAsString 函数取出第1个Post，返回字符串
• getPostAsJson 函数取出第1个Post，返回Post对象
• getPosts 函数取出前2个Post，返回2个Post对象
• createPost 函数创建1个Post，返回字符串
• updatePost 函数更新第1个Post，返回字符串
• deletePost 函数删除第1个Post，返回字符串

生成 json 转换的代码

在工程根目录下执行以下命令

pub run build_runner build

该命令会生成 example.g.dart 文件

// GENERATED CODE - DO NOT MODIFY BY HAND

part of 'example.dart';

// **************************************************************************
// JsonSerializableGenerator
// **************************************************************************

Post _$PostFromJson(Map<String, dynamic> json) {
  return Post()
    ..userId = json['userId'] as int
    ..id = json['id'] as int
    ..title = json['title'] as String
    ..body = json['body'] as String;
}

Map<String, dynamic> _$PostToJson(Post instance) => <String, dynamic>{
      'userId': instance.userId,
      'id': instance.id,
      'title': instance.title,
      'body': instance.body,
    };

输出

程序执行后的输出为

{
  "userId": 1,
  "id": 1,
  "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
  "body": "quia et suscipit
suscipit recusandae consequuntur expedita et cum
reprehenderit molestiae ut ut quas totam
nostrum rerum est autem sunt rem eveniet architecto"
}
Post {userId = 1, id = 1, title = "sunt aut facere repellat provident occaecati excepturi optio reprehenderit", body = "quia et suscipit
suscipit recusandae consequuntur expedita et cum
reprehenderit molestiae ut ut quas totam
nostrum rerum est autem sunt rem eveniet architecto"}
[Post {userId = 1, id = 1, title = "sunt aut facere repellat provident occaecati excepturi optio reprehenderit", body = "quia et suscipit
suscipit recusandae consequuntur expedita et cum
reprehenderit molestiae ut ut quas totam
nostrum rerum est autem sunt rem eveniet architecto"}, Post {userId = 1, id = 2, title = "qui est esse", body = "est rerum tempore vitae
sequi sint nihil reprehenderit dolor beatae ea dolores neque
fugiat blanditiis voluptate porro vel nihil molestiae ut reiciendis
qui aperiam non debitis possimus qui neque nisi nulla"}]
{
  "id": 101
}
{
  "id": 1
}
{}