Unable to create call adapter for class example.Si

Question

I am using retrofit 2.0.0-beta1 with SimpleXml. I want the retrieve a Simple (XML) resource from a REST service. Marshalling/Unmarshalling the Simple object with SimpleXML works fine.

When using this code (converted form pre 2.0.0 code):

final Retrofit rest = new Retrofit.Builder()
    .addConverterFactory(SimpleXmlConverterFactory.create())
    .baseUrl(endpoint)
    .build();
SimpleService service = rest.create(SimpleService.class);
LOG.info(service.getSimple("572642"));

Service:

public interface SimpleService {

    @GET("/simple/{id}")
    Simple getSimple(@Path("id") String id);

}

I get this exception:

Exception in thread "main" java.lang.IllegalArgumentException: Unable to create call adapter for class example.Simple
    for method SimpleService.getSimple
    at retrofit.Utils.methodError(Utils.java:201)
    at retrofit.MethodHandler.createCallAdapter(MethodHandler.java:51)
    at retrofit.MethodHandler.create(MethodHandler.java:30)
    at retrofit.Retrofit.loadMethodHandler(Retrofit.java:138)
    at retrofit.Retrofit$1.invoke(Retrofit.java:127)
    at com.sun.proxy.$Proxy0.getSimple(Unknown Source)

What am i missing? I know that wrapping the return type by a Call works. But I want the service to return business objects as type (and working in sync mode).

UPDATE

After added the extra dependancies and .addCallAdapterFactory(RxJavaCallAdapterFactory.create()) as suggested by different answers, I still get this error:

Caused by: java.lang.IllegalArgumentException: Could not locate call adapter for class simple.Simple. Tried:
 * retrofit.RxJavaCallAdapterFactory
 * retrofit.DefaultCallAdapter$1

Answer 1

If you are not using RxJava it properly makes no sense to add RxJava just for retrofit. 2.5.0 has support for CompletableFuture built in which you can use without adding any other library or adapter.

build.gradle.kts

implementation("com.squareup.retrofit2:retrofit:2.5.0")
implementation("com.squareup.retrofit2:retrofit-converters:2.5.0")

Api.kt

interface Api {
    @GET("/resource")
    fun listCompanies(): CompletableFuture<ResourceDto>
}

Usage:

Retrofit.Builder()
   .addConverterFactory(SimpleXmlConverterFactory.create())
   .baseUrl("https://api.example.com")
   .build()
   .create(Api::class.java)

Answer 2

You can implement a Callback, get the Simple from onResponse function.

public class MainActivity extends Activity implements Callback<Simple> {

    protected void onCreate(Bundle savedInstanceState) {
        final Retrofit rest = new Retrofit.Builder()
                    .addConverterFactory(SimpleXmlConverterFactory.create())
                    .baseUrl(endpoint)
                    .build();
        SimpleService service = rest.create(SimpleService.class);
        Call<Simple> call = service.getSimple("572642");
        //asynchronous call
        call.enqueue(this);

        return true;
    }

    @Override
    public void onResponse(Response<Simple> response, Retrofit retrofit) {
       // response.body() has the return object(s)
    }

    @Override
    public void onFailure(Throwable t) {
        // do something
    }

}

Answer 3

public interface SimpleService {

  @GET("/simple/{id}")
  Simple getSimple(@Path("id") String id);

}

Communication with the network is done with the separate thread so you should change your Simple with that.

public interface SimpleService {

  @GET("/simple/{id}")
  Call<Simple> getSimple(@Path("id") String id);

}

Answer 4

Just to make the Call examples clearer for people who are migrating, not using Rx, or who want synchronous calls - Call essentially replaces (wraps) Response, meaning:

Response<MyObject> createRecord(...);

becomes

Call<MyObject> createRecord(...);

and not

Call<Response<MyObject>> createRecord(...);

(which will still require an adapter)

---

The Call will then allow you to still use isSuccessful as it actually returns a Response. So you can do something like:

myApi.createRecord(...).execute().isSuccessful()

Or access your Type (MyObject) like:

MyObject myObj = myApi.createRecord(...).execute().body();

Answer 5

Add the following dependencies for retrofit 2

 compile 'com.squareup.retrofit2:retrofit:2.1.0'

for GSON

 compile 'com.squareup.retrofit2:converter-gson:2.1.0'

for observables

compile 'com.squareup.retrofit2:adapter-rxjava:2.1.0'

In your case for XML , you would have to include the following dependencies

 compile 'com.squareup.retrofit2:converter-simplexml:2.1.0'

Update the service call as below

final Retrofit rest = new Retrofit.Builder()
    .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
    .addConverterFactory(SimpleXmlConverterFactory.create())
    .baseUrl(endpoint)
    .build();
SimpleService service = rest.create(SimpleService.class);

Answer 6

add dependencies:

compile 'com.squareup.retrofit:retrofit:2.0.0-beta1'
compile 'com.squareup.retrofit:adapter-rxjava:2.0.0-beta1'
compile 'com.squareup.retrofit:converter-gson:2.0.0-beta1'

create your adapter this way:

Retrofit rest = new Retrofit.Builder()
    .baseUrl(endpoint)
    .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
    .addConverterFactory(SimpleXmlConverterFactory.create())
    .build();

addCallAdapterFactory () and addConverterFactory () both need to be called.

Service:

public interface SimpleService {

    @GET("/simple/{id}")
    Call<Simple> getSimple(@Path("id") String id);

}

Modify Simple to Call<Simple>.