Retrofit基本使用

内容

• 基础
• 接口配置
• 发送请求
  • 异步请求 && 示例一
  • Convert && 示例二
  • RxJava支持 && 示例三
• 参考：Retrofit官网

基础

使用Retrofit能够通过添加注解，轻松地将 HTTP API 转化为 Java 接口，示例如下：

    compile 'com.squareup.okhttp3:okhttp:3.8.1'
    compile 'com.squareup.retrofit2:retrofit:2.3.0'

    public interface GitHubService {
    @GET("users/{user}/repos")
    Call<List<Repo>> listRepos(@Path("user") String user);
    }

使用上述接口：

    Retrofit retrofit = new Retrofit.Builder()
        .baseUrl("https://api.github.com/")
        .build();

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

调用 call 的 execute 方法或者 enqueue 方法进行同步或者异步的网络请求：

    Call<List<Repo>> repos = service.listRepos("octocat");
    repos.execute() //同步调用
    repos.enqueue(new Callback<T>() {...}) //异步调用

接口配置

• 使用 @GET, @POST, @PUT, @DELETE, @HEAD 注解来相应标注 HTTP API 的请求类型
• 使用@Path、@Query 注解标注 api url 中的参数

    @GET("group/{id}/users")
    Call<List<User>> groupList(@Path("id") int groupId, @Query("sort") String sort);

• 复杂结构的参数使用 @QueryMap 来标注

    @GET("group/{id}/users")
    Call<List<User>> groupList(@Path("id") int groupId, @QueryMap Map<String, String> options);

• 使用@Body注解 可以将 Java 对象标注为请求体

    @POST("users/new")
    Call<User> createUser(@Body User user);

• 其他注解：
  • @FormUrlEncoded
  • @Multipart
  • @Headers

示例一

使用Gank.io的随机数据接口，实现如下简单的示例：

GankService.java

public interface GankService {
    // http://gank.io/api/random/data/分类/个数
    @GET("random/data/{category}/{number}")
    Call<ResponseBody> getResponseData(@Path("category") String category, @Path("number") String number);
}

GankActivity.java

public class GankActivity extends AppCompatActivity {

    TextView tvGank;

    final String pageSize = "10";

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_gank);
        findViewById(R.id.btn_gank).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getData();
            }
        });
        tvGank = (TextView) findViewById(R.id.tv_gank);
    }

    private void getData() {

        // BaseUrl 需要以 '/' (slash)结尾
        final String baseUrl = "http://gank.io/api/";
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(baseUrl)
                .build();
        GankService service = retrofit.create(GankService.class);

        Call<ResponseBody> call = service.getResponseData("Android", pageSize);

        // call.execute();      // 同步调用
        // call.enqueue();      // 异步调用
        // call.cancel();       // 取消请求
        // call.isCanceled();   // 是否请求
        // call.isExecuted();   // 是否调用

        call.enqueue(new Callback<ResponseBody>() {
            @Override
            public void onResponse(Call<ResponseBody> call, retrofit2.Response<ResponseBody> response) {
                try {
                    tvGank.setText(response.body().string());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public void onFailure(Call<ResponseBody> call, Throwable t) {
                Log.d("corey", "call.enqueue failed:" + t.toString());
            }
        });
    }
}

Converter

• 默认地，若不做 converter 相关配置，Retrofit只能将网络请求的 HTTP body 转化为 OkHttp 中的 ResponseBody 类型，@Body中接收参数也只能接收 ResponseBody 类型
• Retrofit 提供了多种解析库的converter，只需在build时添加配置即可使用，例如，要添加支持Gson解析库从而支持对Json的解析，只需如下：

    compile 'com.google.code.gson:gson:2.8.1'
    compile 'com.squareup.retrofit2:converter-gson:2.3.0'

    Retrofit retrofit = new Retrofit.Builder()
        .baseUrl("https://api.github.com/")
        .addConverterFactory(GsonConverterFactory.create())
        .build();

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

• 除了Retrofit内置支持的各个解析库外，还可以添加自定义的解析库。新建一个类继承自 Converter.Factory ，然后在初始化Retrofit示例时，将该自定义的Converter传入即可。

示例二

GankService.java

public interface GankService {
    // http://gank.io/api/random/data/分类/个数
    @GET("random/data/{category}/{number}")
    Call<GankRandom> getEntityData(@Path("category") String category, @Path("number") String number);
}

GankActivity2.java

public class GankActivity2 extends AppCompatActivity {

    TextView tvGank;
    RecyclerView rvGank;
    SimpleStringAdapter simpleStringAdapter;
    ProgressDialog progressDialog;

    final String pageSize = "10";

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_gank2);
        findViewById(R.id.btn_gank2).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getData();
            }
        });
        tvGank = (TextView) findViewById(R.id.tv_gank2);
        rvGank = (RecyclerView) findViewById(R.id.rv_gank2);
        rvGank.setLayoutManager(new LinearLayoutManager(this));
        simpleStringAdapter = new SimpleStringAdapter(this);
        rvGank.setAdapter(simpleStringAdapter);
        progressDialog = new ProgressDialog(this);
    }

    private void getData() {
        progressDialog.show();
        final String baseUrl = "http://gank.io/api/";
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(baseUrl)
                .addConverterFactory(GsonConverterFactory.create())
                .build();
        GankService service = retrofit.create(GankService.class);
        Call<GankRandom> call = service.getEntityData("Android", pageSize);
        call.enqueue(new Callback<GankRandom>() {
            @Override
            public void onResponse(Call<GankRandom> call, Response<GankRandom> response) {
                List<String> data = new ArrayList<String>();
                for (GankRandom.ResultsBean bean : response.body().getResults()) {
                    data.add(bean.getDesc());
                }
                simpleStringAdapter.setStrings(data);
                progressDialog.dismiss();
            }

            @Override
            public void onFailure(Call<GankRandom> call, Throwable t) {
                Log.d("corey", "call.enqueue failed:" + t.toString());
                progressDialog.dismiss();
            }
        });
    }
}

Retrofit + RxJava

• Retrofit可以配合RxJava使用，具体的使用如下：
  • 定义接口时，将其返回值设为Observable
  • 新建Retrofit实例时，添加RxJava支持

    compile 'io.reactivex.rxjava2:rxandroid:2.0.1'
    compile 'io.reactivex.rxjava2:rxjava:2.0.9'
    compile 'com.squareup.retrofit2:adapter-rxjava2:2.3.0'

    interface GitHubService {
        @GET("users/{user}/repos")
        Observable<List<Repo>> listRepos(@Path("user") String user);
    }

    Retrofit retrofit = new Retrofit.Builder()
        .baseUrl("https://api.github.com/")
        .addConverterFactory(GsonConverterFactory.create())
        .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
        .build();

    GitHubService service = retrofit.create(GitHubService.class);
    service.listRepos("google")
        .subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe(new Observer<List<Repo>>(){...})

示例三

GankService.java

public interface GankService {
    // http://gank.io/api/random/data/分类/个数
    @GET("random/data/{category}/{number}")
    Observable<GankRandom> getObservableData(@Path("category") String category, @Path("number") String number);
}

GankActivity3.java

public class GankActivity3 extends AppCompatActivity {

    TextView tvGank;
    RecyclerView rvGank;
    SimpleStringAdapter simpleStringAdapter;
    Disposable disposable;
    ProgressDialog progressDialog;

    final String pageSize = "10";

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_gank3);
        findViewById(R.id.btn_gank3).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getData();
            }
        });
        tvGank = (TextView) findViewById(R.id.tv_gank3);
        rvGank = (RecyclerView) findViewById(R.id.rv_gank3);
        rvGank.setLayoutManager(new LinearLayoutManager(this));
        simpleStringAdapter = new SimpleStringAdapter(this);
        rvGank.setAdapter(simpleStringAdapter);
        progressDialog = new ProgressDialog(this);
    }

    private void getData() {
        final String baseUrl = "http://gank.io/api/";
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(baseUrl)
                .addConverterFactory(GsonConverterFactory.create())
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .build();
        GankService service = retrofit.create(GankService.class);

        disposable = service.getObservableData("Android", pageSize)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .map(new Function<GankRandom, List<String>>() {

                    @Override
                    public List<String> apply(@NonNull GankRandom gankRandom) throws Exception {
                        List<String> toReturn = new ArrayList<>();
                        for (GankRandom.ResultsBean gankBean : gankRandom.getResults()) {
                            toReturn.add(gankBean.getDesc());
                        }
                        return toReturn;
                    }
                })
                .subscribeWith(
                        new DisposableObserver<List<String>>() {
                            @Override
                            protected void onStart() {
                                progressDialog.show();
                            }

                            @Override
                            public void onNext(@NonNull List<String> titles) {
                                progressDialog.dismiss();
                                simpleStringAdapter.setStrings(titles);
                            }

                            @Override
                            public void onError(@NonNull Throwable e) {
                                progressDialog.dismiss();
                            }

                            @Override
                            public void onComplete() {
                            }
                        }
                );
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (!disposable.isDisposed()) {
            disposable.dispose();
        }
    }
}

参考：Retrofit官网