ohpm install @ohos/retrofit

Retrofit parses HTTP Request class and provides method based api calling. 
As shown below, Create Custom HTTP request class like "DataService" Extending "BaseService".
Retrofit supports API declaration with Decorators, for example to make "GET" api call use @GET. Other api's supported are listed under "API Introduction" below.
Use "retrofit" module to import retrofit apis.

 // Path注解由于和系统组件Path重名，会导致项目编译失败，所以在引用的时候需要修改Path为UrlPath
import {BaseService,ServiceBuilder,GET,POST,DELETE,PUT,UrlPath,Body,BasePath,Response,Header,Query} from '@ohos/retrofit';

//BasePath - Append "/" to basepath.
@BasePath("/")
class DataService extends BaseService{
  
  //GET Api call with Header and Query params
  @GET("get?test=arg123")
  async getRequest(@Header("Content-Type") contentType: string,@Query('d1') data1: string,@Query('d2') data2: number): Promise<Response<Data>> { return <Response<Data>>{} };

  //POST Api call with Header and Body info
  @POST("post")
  async postRequest(@Header("Content-Type") contentType: string,@Body user: User): Promise<Response<Data>> { return <Response<Data>>{} };

  //PUT Api call with Header and Body info
  @PUT("put")
  async putRequest(@Header("Content-Type") contentType: string,@Body user: User): Promise<Response<Data>> { return <Response<Data>>{} };

  //GET Api call with Header, Query and Path Param
  @GET("{req}?test=arg123")
  async getRequest2(@Header("Content-Type") contentType: string,@Query('d1') data1: string,@Query('d2') data2: number,@Path("req") requestPath: string): Promise<Response<Data>> { return <Response<Data>>{} };
}

Initialize the Retrofit BaseService, Set End point and Call required apis by its method.

    const dataService = new ServiceBuilder()
      .setEndpoint("https://restapiservice.com")    //Base Url
      .build(DataService);

    dataService.getRequest("application/json","dat1",8).then((resp)=>{  //Get request with params
        console.log("getRequest Response =" + JSON.stringify(resp.result));
    }

|---- retrofit  
|     |---- entry  # 示例代码文件夹
|     |---- library  # retrofit 库文件夹
|           |---- src # retrofit源码文件夹
|                 |---- # ets
|                         |---- # baseService.ts 服务的基类
|                         |---- # constants.ts 存放retrofit数据类型、interface等常量
|                         |---- # dataResolver.ts 基础数据解析器，支持的解析器类型为JSON和XML
|                         |---- # decorators.ts  装饰器，注解的封装
|           |---- index.ts  # retrofit对外接口
|     |---- README.MD  # 安装使用方法