Android网络通讯之Retrofit

Retrofit本身并不支持网络通讯。

Retrofit封装了OkHttp，让网络请求更加简单。

Retrofit通过接口+注解的方式，封装了重复的代码。

封装了Gson，可以直接将返回的json字符串转换成Java对象

结合rxjava，实现响应式编程

使用Retrofit进行网络通讯就好像使用SpringCloud中的Openfeign

官网地址：https://square.github.io/retrofit/

使用步骤

准备

1、在build.gradle中引入依赖implementation 'com.squareup.retrofit2:retrofit:2.9.0'

2、在AndroidManifest.xml中添加网络请求权限<uses-permission android:name="android.permission.INTERNET"/>

一、简单使用

使用 https://www.httpbin.org/ 作为我们的测试接口地址

1、创建接口类

@POST 声明为post请求，实际请求地址会拼接成 https://www.httpbin.org/post, 通过@FormUrlEncoded和@Field声明表单请求参数；@Body声明Body参数。

@GET 声音为get请求，实际请求地址会拼接成 https://www.httpbin.org/get, 通过@Query声明请求参数。

import okhttp3.RequestBody;
import okhttp3.ResponseBody;
import retrofit2.Call;
import retrofit2.http.Body;
import retrofit2.http.Field;
import retrofit2.http.FormUrlEncoded;
import retrofit2.http.GET;
import retrofit2.http.POST;
import retrofit2.http.Query;public interface HttpbinService {@POST("post")@FormUrlEncodedCall<ResponseBody> post(@Field("username") String username, @Field("password")  String pwd);@GET("get")Call<ResponseBody> get(@Query("username") String username,@Query("password")  String pwd);@POST("post")Call<ResponseBody> postBody(@Body RequestBody requestBody);
}

2、在Android程序中使用

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import androidx.appcompat.app.AppCompatActivity;
import java.io.IOException;
import okhttp3.ResponseBody;
import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Retrofit;public class MainActivity extends AppCompatActivity {private Retrofit retrofit;private HttpbinService httpbinService;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);retrofit = new Retrofit.Builder().baseUrl("https://www.httpbin.org/").build();httpbinService = retrofit.create(HttpbinService.class);}/*** 异步Get请求*/public void getAsync(View view) {Call<ResponseBody> resp = httpbinService.get("test", "123123");resp.enqueue(new Callback<ResponseBody>() {@Overridepublic void onResponse(Call<ResponseBody> call, retrofit2.Response<ResponseBody> response) {try {Log.d("test", "getAsync: " + response.body().string());} catch (IOException e) {e.printStackTrace();}}@Overridepublic void onFailure(Call<ResponseBody> call, Throwable t) {Log.d("test", "getAsync error: " + t.getMessage());}});}/*** 异步Post请求*/public void postAsync(View view) {Call<ResponseBody> resp = httpbinService.post("test", "123123");resp.enqueue(new Callback<ResponseBody>() {@Overridepublic void onResponse(Call<ResponseBody> call, retrofit2.Response<ResponseBody> response) {try {Log.d("test", "postAsync: " + response.body().string());} catch (IOException e) {e.printStackTrace();}}@Overridepublic void onFailure(Call<ResponseBody> call, Throwable t) {Log.d("test", "postAsync error: " + t.getMessage());}});}}

二、配合Gson 以及 Rxjava，返回java对象和响应式编程

在build.gradle中引入依赖

implementation 'com.squareup.retrofit2:converter-gson:2.9.0'
implementation 'com.squareup.retrofit2:adapter-rxjava3:2.9.0'
implementation 'io.reactivex.rxjava3:rxandroid:3.0.0'

本例中使用 https://www.wanandroid.com/ 测试接口调用

1、添加测试接口类

import io.reactivex.rxjava3.core.Flowable;
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.Path;public interface WanAndroidTestService {/**正常返回 Java对象 */@POST("/user/login")@FormUrlEncodedCall<LoginUser> login(@Field("username") String username, @Field("password") String password);/**通过RxJava响应式返回 Java对象 */@POST("/user/login")@FormUrlEncodedFlowable<LoginUser> login2(@Field("username") String username, @Field("password") String password);/**通过RxJava响应式返回 ResponseBody */@GET("lg/collect/list/{pageNum}/json")Flowable<ResponseBody> getArticle(@Path("pageNum") int pageNum);
}

2、测试使用，返回Java对象

添加转换器 addConverterFactory(GsonConverterFactory.create())

public class WanAndroidUnitTest {Retrofit retrofit = new Retrofit.Builder().baseUrl("https://www.wanandroid.com/").addConverterFactory(GsonConverterFactory.create())//添加转换器.build();WanAndroidTestService wanAndroidService = retrofit.create(WanAndroidTestService.class);@Testpublic void login() throws IOException {Response<LoginUser> response = wanAndroidService.login("xxxxx", "xxxxx").execute();LoginUser loginUser = response.body();System.out.println("loginUser = " + loginUser);}
}

3、配合RxJava使用，并使用cookie

添加Cookie支持
添加Gson转换器addConverterFactory(GsonConverterFactory.create())
添加RxJava适配器addCallAdapterFactory(RxJava3CallAdapterFactory.create())

本示例代码使用www.wanandroid.com的开放接口，可以自行去注册一个账号用于测试

import io.reactivex.rxjava3.functions.Consumer;
import io.reactivex.rxjava3.functions.Function;
import io.reactivex.rxjava3.schedulers.Schedulers;
import okhttp3.Cookie;
import okhttp3.CookieJar;
import okhttp3.HttpUrl;
import okhttp3.OkHttpClient;
import okhttp3.ResponseBody;
import retrofit2.Retrofit;
import retrofit2.adapter.rxjava3.RxJava3CallAdapterFactory;
import retrofit2.converter.gson.GsonConverterFactory;public class RetrofitCookieUnitTest {Map<String, List<Cookie>> cookies = new HashMap<>();Retrofit retrofit = new Retrofit.Builder().baseUrl("https://www.wanandroid.com/")// 添加Cookie支持.callFactory(new OkHttpClient.Builder().cookieJar(new CookieJar() {@Overridepublic void saveFromResponse(HttpUrl url, List<Cookie> list) {cookies.put(url.host(), list);}@Overridepublic List<Cookie> loadForRequest(HttpUrl url) {List<Cookie> list = cookies.get(url.host());return list == null ? new ArrayList<>() : list;}}).build())//添加Gson转换器.addConverterFactory(GsonConverterFactory.create())//添加RxJava适配器.addCallAdapterFactory(RxJava3CallAdapterFactory.create()).build();WanAndroidTestService androidTestService = retrofit.create(WanAndroidTestService.class);@Testpublic void rxTest() throws IOException {androidTestService.login2("xxxxx", "xxxxx")// 登录成功后，执行下一步操作，查询收藏文章列表.flatMap(new Function<LoginUser, Publisher<ResponseBody>>() {@Overridepublic Publisher<ResponseBody> apply(LoginUser loginUser) throws Throwable {return androidTestService.getArticle(0);}}).observeOn(Schedulers.io())// 如果是Android环境需要切换到Android的主线程// .subscribeOn(AndroidSchedulers.mainThread())// 这里是Junit，切换到新的线程.subscribeOn(Schedulers.newThread())// 订阅返回结果，并打印输出.subscribe(new Consumer<ResponseBody>() {@Overridepublic void accept(ResponseBody responseBody) throws Throwable {System.out.println(responseBody.string());}});while (true) {}}
}

4、文件上传、下载

文件上传

使用注解@Multipart和@Part实现文件上传

1）创建请求接口

import okhttp3.MultipartBody;
import okhttp3.ResponseBody;
import retrofit2.Call;
import retrofit2.http.Multipart;
import retrofit2.http.POST;
import retrofit2.http.Part;public interface UploadFileService {@POST("post")@MultipartCall<ResponseBody> upload(@Part MultipartBody.Part part);
}

2）编写测试代码

public class UploadFileTest {Retrofit retrofit = new Retrofit.Builder().baseUrl("https://www.httpbin.org/").build();UploadFileService uploadFileService = retrofit.create(UploadFileService.class);@Testpublic void upload() throws IOException {File file1 = new File("d:/temp/1.txt");MultipartBody.Part part = MultipartBody.Part.createFormData("file1", file1.getName(),RequestBody.create(MediaType.parse("text/plain"), file1));Call<ResponseBody> resp = uploadFileService.upload(part);System.out.println("resp = " + resp.execute().body().string());}
}

文件下载

Call 常规下载
Flowable 通过RxJava方式下载，需要添加RxJava适配器

如果下载的文件很大，需要增加注解 @Streaming避免出现内存溢出

1）创建请求接口

import io.reactivex.rxjava3.core.Flowable;
import okhttp3.MultipartBody;
import okhttp3.ResponseBody;
import retrofit2.Call;
import retrofit2.http.GET;
import retrofit2.http.Multipart;
import retrofit2.http.POST;
import retrofit2.http.Part;
import retrofit2.http.Streaming;
import retrofit2.http.Url;public interface UploadFileService {@POST("post")@MultipartCall<ResponseBody> upload(@Part MultipartBody.Part part);@GETCall<ResponseBody> download(@Url String url);@Streaming@GETFlowable<ResponseBody> downloadRxJava(@Url String url);
}

2）创建测试用例

import org.junit.Test;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import io.reactivex.rxjava3.functions.Consumer;
import io.reactivex.rxjava3.functions.Function;
import okhttp3.ResponseBody;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.adapter.rxjava3.RxJava3CallAdapterFactory;public class DownloadFileTest {Retrofit retrofit = new Retrofit.Builder().baseUrl("https://www.httpbin.org/")//添加RxJava适配器.addCallAdapterFactory(RxJava3CallAdapterFactory.create()).build();UploadFileService uploadFileService = retrofit.create(UploadFileService.class);@Testpublic void download() throws IOException {Response<ResponseBody> response = uploadFileService.download("https://www.dasouji.com/wp-content/uploads/2020/12/@ukwanghyun.jpg").execute();if (!response.isSuccessful()) {System.out.println("下载失败，" + response.code());return;}InputStream inputStream = response.body().byteStream();FileOutputStream fos = new FileOutputStream("d:/temp/3.jpg");int len;byte[] buffer = new byte[4096];while ((len = inputStream.read(buffer)) != -1) {fos.write(buffer, 0, len);}fos.close();inputStream.close();System.out.println("下载完成，" + response.code());}@Testpublic void downloadRxJava() throws IOException {uploadFileService.downloadRxJava("https://www.dasouji.com/wp-content/uploads/2020/12/@ukwanghyun.jpg")// 将结果映射成File对象.map(new Function<ResponseBody, File>() {@Overridepublic File apply(ResponseBody responseBody) throws Throwable {InputStream inputStream = responseBody.byteStream();File file = new File("d:/temp/4.jpg");FileOutputStream fos = new FileOutputStream(file);int len;byte[] buffer = new byte[4096];while ((len = inputStream.read(buffer)) != -1) {fos.write(buffer, 0, len);}fos.close();inputStream.close();System.out.println("下载完成！");return file;}})// 获取下载结果.subscribe(new Consumer<File>() {@Overridepublic void accept(File file) throws Throwable {System.out.println("获取下载文件！" + file.getName());}});while (true) {}}
}

Retrofit的注解

方法注解：@GET，@POST，@PUT，@DELETE，@PATH，@HEAD，@OPTIONS，@HTTP
标记注解：@FormUrlEncoded，@Multipart，@Streaming
参数注解：@Query，@Field，@Body，@FieldMap，@QueryMap，@Part，@PartMap
其他注解：@Path，@Header，@Headers，@Url