Set Dynamic Base Url Using Retrofit 2.0 and Dagger 2

Set dynamic base url using Retrofit 2.0 and Dagger 2

Support for this use-case was removed in Retrofit2. The recommendation is to use an OkHttp interceptor instead.

HostSelectionInterceptor made by swankjesse

import java.io.IOException;
import okhttp3.HttpUrl;
import okhttp3.Interceptor;
import okhttp3.OkHttpClient;
import okhttp3.Request;

/** An interceptor that allows runtime changes to the URL hostname. */
public final class HostSelectionInterceptor implements Interceptor {
  private volatile String host;

  public void setHost(String host) {
    this.host = host;
  }

  @Override public okhttp3.Response intercept(Chain chain) throws IOException {
    Request request = chain.request();
    String host = this.host;
    if (host != null) {
      //HttpUrl newUrl = request.url().newBuilder()
      //    .host(host)
      //    .build();
      HttpUrl newUrl = HttpUrl.parse(host);
      request = request.newBuilder()
          .url(newUrl)
          .build();
    }
    return chain.proceed(request);
  }

  public static void main(String[] args) throws Exception {
    HostSelectionInterceptor interceptor = new HostSelectionInterceptor();

    OkHttpClient okHttpClient = new OkHttpClient.Builder()
        .addInterceptor(interceptor)
        .build();

    Request request = new Request.Builder()
        .url("http://www.coca-cola.com/robots.txt")
        .build();

    okhttp3.Call call1 = okHttpClient.newCall(request);
    okhttp3.Response response1 = call1.execute();
    System.out.println("RESPONSE FROM: " + response1.request().url());
    System.out.println(response1.body().string());

    interceptor.setHost("www.pepsi.com");

    okhttp3.Call call2 = okHttpClient.newCall(request);
    okhttp3.Response response2 = call2.execute();
    System.out.println("RESPONSE FROM: " + response2.request().url());
    System.out.println(response2.body().string());
  }
}

Or you can either replace your Retrofit instance (and possibly store the instance in a RetrofitHolder in which you can modify the instance itself, and provide the holder through Dagger)...

public class RetrofitHolder {
   Retrofit retrofit;

   //getter, setter
}

Or re-use your current Retrofit instance and hack the new URL in with reflection, because screw the rules. Retrofit has a baseUrl parameter which is private final, therefore you can access it only with reflection.

Field field = Retrofit.class.getDeclaredField("baseUrl");
field.setAccessible(true);
okhttp3.HttpUrl newHttpUrl = HttpUrl.parse(newUrl);
field.set(retrofit, newHttpUrl);

Dagger + Retrofit dynamic URL

I see 2 options here:

• Use dagger as it is intended. Create for every baseUrl their own Retrofit client, or
• Use an interceptor to modify the request before sending it

Dagger approach

If you were to brute force urls, this would probably not be the right choice, since it relies on creating a new Retrofit instance for each.

Now every time the url changes, you just recreate the following demonstrated UrlComponent by supplying it with a new UrlModule.

Clean up

Clean your @Singleton module, so that it provides GsonConverterFactory, and RxJavaCallAdapterFactory to make proper use of dagger and not recreate shared objects.

@Module
public class SingletonModule {

  @Provides
  @Singleton
  GsonConverterFactory provideOkHttpClient() {/**/}

  @Provides
  @Singleton
  RxJavaCallAdapterFactory provideOkHttpClient() {/**/}
}

@Singleton
@Component(modules = SingletonModule.class)
interface SingletonComponent {

    // sub component
    UrlComponent plus(UrlModule component);
}

Url Scoped

Introduce a @UrlScope to scope your Retrofit instances.

@Scope
@Retention(RetentionPolicy.RUNTIME)
public @interface UrlScope {
}

Then create a subcomponent

@SubComponent(modules=UrlModule.class)
public interface UrlComponent {}

And a module for it

@Module
class UrlModule {

    private final String mUrl;

    UrlModule(String url) { mUrl = url; }

    @Provides
    String provideUrl() {
        return mUrl;
    }

    @Provides
    @UrlScope
    OkHttpClient provideOkHttpClient(String url) {
        return new OkHttpClient.Builder().build();
    }

    @Provides
    @UrlScope
    Retrofit provideRetrofit(OkHttpClient client) {
        return new Retrofit.Builder().build();
    }

}

Use scoped Retrofit

Instantiate the component and use it.

class Dagger {

    public void demo() {
        UrlModule module = new UrlModule(/*some url*/);
        SingletonComponent singletonComponent = DaggerSingletonComponent.create();
        UrlComponent urlComponent = singletonComponent.plus(module);

        urlComponent.getRetrofit(); // done.
    }
}

OkHttp approach

Provide a properly scoped interceptor (@Singleton in this case) and implement the corresponding logic.

@Module
class SingletonModule {

    @Provides
    @Singleton
    GsonConverterFactory provideGsonConverter() { /**/ }

    @Provides
    @Singleton
    RxJavaCallAdapterFactory provideRxJavaCallAdapter() { /**/ }

    @Provides
    @Singleton
    MyApiInterceptor provideMyApiInterceptor() { /**/ }

    @Provides
    @Singleton
    OkHttpClient provideOkHttpClient(MyApiInterceptor interceptor) {
        return new OkHttpClient.Builder().build();
    }

    @Provides
    @Singleton
    Retrofit provideRetrofit(OkHttpClient client) {
        return new Retrofit.Builder().build();
    }
}

@Singleton
@Component(modules = SingletonModule.class)
interface SingletonComponent {

    Retrofit getRetrofit();

    MyApiInterceptor getInterceptor();
}

todo Implement the MyApiInterceptor. You will need to have a setter for the base url, and then just rewrite / modify the requests coming through.

Then, again, just go ahead and use it.

class Dagger {

    public void demo() {
        SingletonComponent singletonComponent = DaggerSingletonComponent.create();
        MyService service = singletonComponent.getRetrofit().create(MyService.class);
        MyApiInterceptor interceptor = singletonComponent.getInterceptor();

        interceptor.setBaseUrl(myUrlA);
        service.doA();
        interceptor.setBaseUrl(someOtherUrl);
        service.doB();
    }
}

As a third approach, you could also use reflection to just directly change base the base URL—I added this last just for completeness.

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