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：

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 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 , 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 , 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")    @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);    @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;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        retrofit = new Retrofit.Builder().baseUrl(";).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>() {            @Override            public void onResponse(Call<ResponseBody> call, retrofit2.Response<ResponseBody> response) {                try {                    Log.d("test", "getAsync: " + response.body().string());                } catch (IOException e) {                    e.printStackTrace();                }            }            @Override            public 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>() {            @Override            public void onResponse(Call<ResponseBody> call, retrofit2.Response<ResponseBody> response) {                try {                    Log.d("test", "postAsync: " + response.body().string());                } catch (IOException e) {                    e.printStackTrace();                }            }            @Override            public 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 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")    @FormUrlEncoded    Call<LoginUser> login(@Field("username") String username, @Field("password") String password);    /**通过RxJava响应式返回 Java对象 */    @POST("/user/login")    @FormUrlEncoded    Flowable<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(";)            .addConverterFactory(GsonConverterFactory.create())//添加转换器            .build();    WanAndroidTestService wanAndroidService = retrofit.create(WanAndroidTestService.class);    @Test    public 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(";)            // 添加Cookie支持            .callFactory(new OkHttpClient.Builder().cookieJar(new CookieJar() {                @Override                public void saveFromResponse(HttpUrl url, List<Cookie> list) {                    cookies.put(url.host(), list);                }                @Override                public 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);    @Test    public 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>>() {                    @Override                    public 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>() {                    @Override                    public 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")    @Multipart    Call<ResponseBody> upload(@Part MultipartBody.Part part);}

2）编写测试代码

public class UploadFileTest {    Retrofit retrofit = new Retrofit.Builder().baseUrl(";).build();    UploadFileService uploadFileService = retrofit.create(UploadFileService.class);    @Test    public 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")    @Multipart    Call<ResponseBody> upload(@Part MultipartBody.Part part);    @GET    Call<ResponseBody> download(@Url String url);    @Streaming    @GET    Flowable<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(";)            //添加RxJava适配器            .addCallAdapterFactory(RxJava3CallAdapterFactory.create())            .build();    UploadFileService uploadFileService = retrofit.create(UploadFileService.class);    @Test    public void download() throws IOException {        Response<ResponseBody> response = uploadFileService.download(";)                .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());    }    @Test    public void downloadRxJava() throws IOException {        uploadFileService.downloadRxJava(";)                // 将结果映射成File对象                .map(new Function<ResponseBody, File>() {                    @Override                    public 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>() {                    @Override                    public 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