Retrofit：基于OkHttp的RESTful风格API的网络框架封装

一.Retrofit介绍

• Retrofit是Square公司基于RESTful风格推出的网络框架封装
• Retrofit与OKHttp的关系：Retrofit是基于OKHttp的网络请求框架的二次封装，其本质仍是OKHttp
• 与其他网络库的对比
  
  • AndroidAsynHttp：基于HttpClient，作者停止维护，Android5.0不再使用HttpClient，因此不推荐
  • Volley：基于HttpUrlConnection，Google官方推出，只适合轻量级网络交互如数据传输小，不适合大文件下上传场景
  • Retrofit优点：API设计简洁易用、注解化配置高度解耦、支持多种解析器、支持Rxjava

二.Retrofit使用

1.开源库集成

• 依赖包导入：

compile 'com.squareup.retrofit2:retrofit:2.2.0'
compile 'com.squareup.okhttp3:okhttp:3.4.1'
compile 'com.squareup.retrofit2:converter-gson:2.0.2'

• 导入方式：

  File -> project structure -> app -> dependencies -> 左下方有一个加号，点击选择Library dependency输入上方的包文件即可

• 添加网络权限：

2.创建接口设置请求类型与参数

• 新建TestModel类（服务端返回的实体对象）和TestService接口样例如下

  @GET("login")
  public Call login(@Query("username")String username,@Query("pwd")String pwd);

• 常见参数注解

  • @GET、@POST确定请求方式
  • @Path请求URL的字符替代
  • @Query要传递的参数
  • @QueryMap包含多个@Query注解参数
  • @Body添加实体类对象
  • @FormUrlEncodedURL编码

3.创建Retrofit对象、设置数据解析器

Retrofit retrofit = new Retrofit.Builder().baseUrl(Constants.BASE_URL).addConverterFactory(GsonConverterFactory.create()).build();

4.生成接口对象

TestService service = retrofit.create(TestService.class);

5.调用接口方法返回Call对象

Callcall = service.login("zhangsan","123456");

6.发送请求（同步、异步）

• 同步：调用Call对象的execute()，返回结果的响应体（默认将代码放入主线程，而安卓4.0后不允许在主线程中执行耗时操作，故应新建一个线程，将请求代码放入）
• 异步：调用Call对象的enqueue()，参数是一个Callback回调函数

7.处理返回的数据

三.Retrofit案例

• 服务端采用SSM框架写的controller层用于测试接口与返回数据

  package controller.admin;
  import org.springframework.stereotype.Controller;
  import org.springframework.web.bind.annotation.PathVariable;
  import org.springframework.web.bind.annotation.RequestMapping;
  import org.springframework.web.bind.annotation.RequestMethod;
  import org.springframework.web.bind.annotation.RequestParam;
  import org.springframework.web.bind.annotation.ResponseBody;
  @Controller
  @RequestMapping("/test")
  public class testController {
  @ResponseBody
  @RequestMapping(value="/get",method=RequestMethod.GET)
  public ReturnObject testGet() {
      ReturnObject ro = new ReturnObject(true,"test");
      return ro;
  }
  
  @ResponseBody
  @RequestMapping(value="/post",method=RequestMethod.POST)
  public ReturnObject testPost(@RequestParam("testname")String testname) {
      ReturnObject ro = new ReturnObject(true,testname);
      return ro;
  }
  
  @ResponseBody
  @RequestMapping(value="/put/{name}",method=RequestMethod.PUT)
  public ReturnObject testPut(@PathVariable("name")String testname) {
      ReturnObject ro = new ReturnObject(true,testname);
      return ro;
  }
  
  @ResponseBody
  @RequestMapping(value="/delete/{name}",method=RequestMethod.DELETE)
  public ReturnObject testDelete(@PathVariable("name")String testname) {
      ReturnObject ro = new ReturnObject(true,testname);
      return ro;
  }
  }
  
  class ReturnObject{
  private boolean status;
  private String info;
  public boolean isStatus() {
      return status;
  }
  public void setStatus(boolean status) {
      this.status = status;
  }
  public String getInfo() {
      return info;
  }
  public void setInfo(String info) {
      this.info = info;
  }
  @Override
  public String toString() {
      return "ReturnObject [status=" + status + ", info=" + info + "]";
  }
  public ReturnObject(boolean status, String info) {
      super();
      this.status = status;
      this.info = info;
  }
  }

• 创建Contants类，定义访问主机及端口号

  package c.e.retrofittest;
  public class Contants {
    public static String BASE_URL = "http://192.168.1.104:8080/";
  }

• 定义TestModel实体类

  package c.e.retrofittest;
  public class TestModel {
    private boolean status;
    private String info;
    public boolean isStatus() {
        return status;
    }
    public void setStatus(boolean status) {
        this.status = status;
    }
    public String getInfo() {
        return info;
    }
    public void setInfo(String info) {
        this.info = info;
    }
    @Override
    public String toString() {
        return "TestModel{" +
                "status=" + status +
                ", info='" + info + '\'' +
                '}';
    }
  }

• 定义TestService请求接口【注意：POST请求必须加入@FormUrlEncoded注解，且请求体中内容字段用@Field修饰；GET请求参数用@Query修饰；PUT和DELETE请求URL上的参数用@Path修饰】

  package c.e.retrofittest;
  
  import retrofit2.Call;
  import retrofit2.http.DELETE;
  import retrofit2.http.Field;
  import retrofit2.http.FormUrlEncoded;
  import retrofit2.http.GET;
  import retrofit2.http.POST;
  import retrofit2.http.PUT;
  import retrofit2.http.Part;
  import retrofit2.http.Path;
  import retrofit2.http.Query;
  
  public interface TestService {
  
    @GET("Ui-Gui/test/get")
    public Call test();
  
    @POST("Ui-Gui/test/post")
    @FormUrlEncoded
    public Call testpost(@Field("testname")String testname);
  
    @PUT("Ui-Gui/test/put/{name}")
    public Call testput(@Path("name") String name);
  
    @DELETE("Ui-Gui/test/delete/{name}")
    public Call testdelete(@Path("name") String name);
  }
  

• MainActivity的布局文件

  
  <LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="c.e.retrofittest.MainActivity">
  
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="GET"
        android:onClick="onAction"/>
  
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="POST"
        android:onClick="onPost"/>
  
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="PUT"
        android:onClick="onPut"/>
  
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="DELETE"
        android:onClick="onDelete"/>
  LinearLayout>

• 在MainActivity中执行对应发送请求的步骤

  package c.e.retrofittest;
  
  import android.app.AlertDialog;
  import android.support.v7.app.AppCompatActivity;
  import android.os.Bundle;
  import android.view.View;
  
  import junit.framework.Test;
  
  import java.io.IOException;
  
  import retrofit2.Call;
  import retrofit2.Callback;
  import retrofit2.Response;
  import retrofit2.Retrofit;
  import retrofit2.converter.gson.GsonConverterFactory;
  
  public class MainActivity extends AppCompatActivity {
  
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
  
    public void onAction(View view) throws IOException {
        //创建Retrofit对象
        Retrofit retrofit = new Retrofit.Builder().baseUrl(Contants.BASE_URL).addConverterFactory(GsonConverterFactory.create()).build();
        //生成接口对象
        TestService service = retrofit.create(TestService.class);
        //调用接口方法返回Call对象
        final Call call = service.test();
        //发送同步请求
  //        new Thread(new Runnable() {
  //            @Override
  //            public void run() {
  //                Responseresponse = null;
  //                try {
  //                    response = call.execute();
  //                } catch (IOException e) {
  //                    e.printStackTrace();
  //                }
  //                System.out.println(response.body());
  //            }
  //        }).start();
        //发布异步请求
        call.enqueue(new Callback() {
            @Override
            public void onResponse(Call call, Response response) {
                System.out.println(response.body());
            }
  
            @Override
            public void onFailure(Call call, Throwable t) {
  
            }
        });
    }
  
    public void onPost(View view) throws IOException {
        //创建Retrofit对象
        Retrofit retrofit = new Retrofit.Builder().baseUrl(Contants.BASE_URL).addConverterFactory(GsonConverterFactory.create()).build();
        //生成接口对象
        TestService service = retrofit.create(TestService.class);
        //调用接口方法返回Call对象
        final Call call = service.testpost("this is post");
        //发布异步请求
        call.enqueue(new Callback() {
            @Override
            public void onResponse(Call call, Response response) {
                System.out.println(response.body());
            }
  
            @Override
            public void onFailure(Call call, Throwable t) {
  
            }
        });
    }
  
    public void onPut(View view) throws IOException {
        //创建Retrofit对象
        Retrofit retrofit = new Retrofit.Builder().baseUrl(Contants.BASE_URL).addConverterFactory(GsonConverterFactory.create()).build();
        //生成接口对象
        TestService service = retrofit.create(TestService.class);
        //调用接口方法返回Call对象
        final Call call = service.testput("putResult");
        //发布异步请求
        call.enqueue(new Callback() {
            @Override
            public void onResponse(Call call, Response response) {
                System.out.println(response.body());
            }
  
            @Override
            public void onFailure(Call call, Throwable t) {
  
            }
        });
    }
  
    public void onDelete(View view) throws IOException {
        //创建Retrofit对象
        Retrofit retrofit = new Retrofit.Builder().baseUrl(Contants.BASE_URL).addConverterFactory(GsonConverterFactory.create()).build();
        //生成接口对象
        TestService service = retrofit.create(TestService.class);
        //调用接口方法返回Call对象
        final Call call = service.testdelete("this is what I want delete");
        //发布异步请求
        call.enqueue(new Callback() {
            @Override
            public void onResponse(Call call, Response response) {
                System.out.println(response.body());
            }
  
            @Override
            public void onFailure(Call call, Throwable t) {
  
            }
        });
    }
  }

四.内容总结

• Retrofit是基于Okhttp网络库的高级封装
• 采用注解、网络请求参数配置更灵活、扩展性更好
• RESTful风格的API优先选用Retrofit