41.Retrofit的基本使用

压缩包

HttpbinService.java

MainActivity.java

一、Retrofit简介

A type-safe HTTP client for Android and Java。封装了OkHttp，也是由Square公司贡献的一个处理网络请求的开源项目。

[https://github.com/square/retrofit](https://github.com/square/retrofit)

1.依赖包：

implementation 'com.squareup.retrofit2:retrofit:2.9.0'<br />![image.png](https://cdn.nlark.com/yuque/0/2021/png/1574587/1625399278549-9de9c499-831a-4fa8-84cc-920d89577410.png#clientId=uda9bcb36-7a6d-4&from=paste&height=562&id=u01b00bd4&margin=%5Bobject%20Object%5D&name=image.png&originHeight=562&originWidth=1365&originalType=binary&ratio=1&size=98728&status=done&style=none&taskId=u4286eaf9-a05a-4004-92ad-b30bdf985b4&width=1365)

二、Retrofit基本使用一

服务器域名：[https://www.httpbin.org/](https://www.httpbin.org/)<br />    接口：post<br />    参数：username，possword<br />    接口：get<br />    参数：username，possword

1.根据接口创建Java接口：

三、Retrofit基本使用二

2.创建Retrofit配置，并生成接口实现类对象：

    Retrofit retrofit=new Retrofit.Builder().baseUrl("https://www.httpbin.org/").build();<br />        HttpbinService httpbinService=retrofit.create(HttpbinService.class);

3.接口实现类对象调用对应方法获得响应：

四、Retrofit实现的具体步骤：

1.创建retrofit请求的接口类

2.定义retrofit和请求的接口类

3.实现retrofit的post和callback方法

五、整体代码

1.HttpbinService接口类文件代码

package com.example.networkdemo;
import okhttp3.ResponseBody;
import retrofit2.Call;
import retrofit2.http.Field;
import retrofit2.http.FormUrlEncoded;
import retrofit2.http.GET;
import retrofit2.http.POST;
import retrofit2.http.Query;
public interface HttpbinService {
   // https://www.httpbin.org/post     password=value
   @POST("post")
   @FormUrlEncoded
   Call<ResponseBody> post(@Field("username") String username,@Field("password") String pwd);
   @GET("get")
   Call<ResponseBody> get(@Query("username") String username,@Query("password") String pwd);
}

2.MainActivity文件代码

package com.example.networkdemo;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import org.jetbrains.annotations.NotNull;
import java.io.IOException;
import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.FormBody;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
import okhttp3.ResponseBody;
import retrofit2.Retrofit;
public class MainActivity extends AppCompatActivity {
    // 请求器
    private OkHttpClient okHttpClient;
    private static final String TAG="MainActivity";
    private Retrofit retrofit;
    private HttpbinService httpbinService;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        okHttpClient = new OkHttpClient();
        retrofit = new Retrofit.Builder().baseUrl("https://www.httpbin.org/").build();
        httpbinService = retrofit.create(HttpbinService.class);
    }
    public void getSync(View view) {
        new Thread(){
            @Override
            public void run() {
                // 请求对象
                Request request = new Request.Builder().url("https://www.httpbin.org/get?a=1&b=2").build();
                // 准备好请求的Call对象
                Call call = okHttpClient.newCall(request);
                try {
                    // 请求得到的响应
                    Response response = call.execute();
                    Log.i(TAG,"getSync:"+response.body().string());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }.start();
    }
    public void getASync(View view) {
        Request request = new Request.Builder().url("https://www.httpbin.org/get?a=1&a=2").build();
        // 准备好请求的Call对象
        Call call = okHttpClient.newCall(request);
        //异步请求
        call.enqueue(new Callback() {
            @Override
            public void onFailure(@NotNull Call call, @NotNull IOException e) {
            }
            @Override
            public void onResponse(@NotNull Call call, @NotNull Response response) throws IOException {
                if (response.isSuccessful()){
                    Log.i(TAG,"getASync:"+response.body().string());
                }
            }
        });
    }
    public void postSync(View view) {
        new Thread(){
            @Override
            public void run() {
                FormBody formBody = new FormBody.Builder().add("a", "1").add("b", "2").build();
                Request request = new Request.Builder().url("https://www.httpbin.org/post").post(formBody).build();
                // 准备好请求的Call对象
                Call call = okHttpClient.newCall(request);
                try {
                    // 请求得到的响应
                    Response response = call.execute();
                    Log.i(TAG,"postSync:"+response.body().string());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }.start();
    }
    public void postASync(View view) {
//        FormBody formBody = new FormBody.Builder().add("a", "1").add("b", "2").build();
//        Request request = new Request.Builder().url("https://www.httpbin.org/post").post(formBody).build();
//        // 准备好请求的Call对象
//        Call call = okHttpClient.newCall(request);
//        //异步请求
//        call.enqueue(new Callback() {
//            @Override
//            public void onFailure(@NotNull Call call, @NotNull IOException e) {
//
//            }
//
//            @Override
//            public void onResponse(@NotNull Call call, @NotNull Response response) throws IOException {
//                if (response.isSuccessful()) {
//                    Log.i(TAG, "postASync:" + response.body().string());
//                }
//
//            }
//        });
        // retrofit的使用
        retrofit2.Call<ResponseBody> call = httpbinService.post("lance", "123");
        call.enqueue(new retrofit2.Callback<ResponseBody>() {
        @Override
        public void onResponse
             (retrofit2.Call<ResponseBody> call, retrofit2.Response<ResponseBody> response) {
                try {
                    Log.i(TAG, "postASync:" + response.body().string());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            @Override
            public void onFailure(retrofit2.Call<ResponseBody> call, Throwable t) {
            }
        });
    }
}

3.效果图：

六、常见错误

1.retrofit运行时出现以下错误：

2.静态接口需要在Java 8 下才支持使用，所以我们要使用静态接口，就需要在app的build.gradle文件中配置声明，使用Java 8编译。所以需要加入以下代码来声明：

compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_8
    targetCompatibility JavaVersion.VERSION_1_8
}

3.修改如下图所示：