Creates a JSON API Retrofit converter. https://github.com/kamikat/moshi-jsonapi#retrofit

JsonApiConverterFactory.java

package moe.banana.jsonapi2;

import com.squareup.moshi.JsonAdapter;
import com.squareup.moshi.Moshi;
import com.squareup.moshi.Types;

import java.io.IOException;
import java.lang.annotation.Annotation;
import java.lang.reflect.Array;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;

import moe.banana.jsonapi2.ArrayDocument;
import moe.banana.jsonapi2.Document;
import moe.banana.jsonapi2.ObjectDocument;
import moe.banana.jsonapi2.Resource;
import moe.banana.jsonapi2.ResourceIdentifier;
import okhttp3.MediaType;
import okhttp3.RequestBody;
import okhttp3.ResponseBody;
import okio.Buffer;
import retrofit2.Converter;
import retrofit2.Retrofit;

@SuppressWarnings("unchecked")
public final class JsonApiConverterFactory extends Converter.Factory {

    public static JsonApiConverterFactory create() {
        return create(new Moshi.Builder().build());
    }

    public static JsonApiConverterFactory create(Moshi moshi) {
        return new JsonApiConverterFactory(moshi, false);
    }

    private final Moshi moshi;
    private final boolean lenient;

    private JsonApiConverterFactory(Moshi moshi, boolean lenient) {
        if (moshi == null) throw new NullPointerException("moshi == null");
        this.moshi = moshi;
        this.lenient = lenient;
    }

    public JsonApiConverterFactory asLenient() {
        return new JsonApiConverterFactory(moshi, true);
    }

    private JsonAdapter<?> getAdapterFromType(Type type) {
        Class<?> rawType = Types.getRawType(type);
        JsonAdapter<?> adapter;
        if (rawType.isArray() && ResourceIdentifier.class.isAssignableFrom(rawType.getComponentType())) {
            adapter = moshi.adapter(Types.newParameterizedType(Document.class, rawType.getComponentType()));
        } else if (List.class.isAssignableFrom(rawType) && type instanceof ParameterizedType) {
            Type typeParameter = ((ParameterizedType) type).getActualTypeArguments()[0];
            if (typeParameter instanceof Class<?> && ResourceIdentifier.class.isAssignableFrom((Class<?>) typeParameter)) {
                adapter = moshi.adapter(Types.newParameterizedType(Document.class, typeParameter));
            } else {
                return null;
            }
        } else if (ResourceIdentifier.class.isAssignableFrom(rawType)) {
            adapter = moshi.adapter(Types.newParameterizedType(Document.class, rawType));
        } else if (Document.class.isAssignableFrom(rawType)) {
            adapter = moshi.adapter(Types.newParameterizedType(Document.class, Resource.class));
        } else {
            return null;
        }
        return adapter;
    }

    @Override
    public Converter<ResponseBody, ?> responseBodyConverter(Type type, Annotation[] annotations, Retrofit retrofit) {
        JsonAdapter<?> adapter = getAdapterFromType(type);
        if (adapter == null) {
            return null;
        }
        if (lenient) {
            adapter = adapter.lenient();
        }
        return new MoshiResponseBodyConverter<>((JsonAdapter<Document<?>>) adapter, type);
    }

    @Override
    public Converter<?, RequestBody> requestBodyConverter(Type type, Annotation[] parameterAnnotations, Annotation[] methodAnnotations, Retrofit retrofit) {
        JsonAdapter<?> adapter = getAdapterFromType(type);
        if (adapter == null) {
            return null;
        }
        if (lenient) {
            adapter = adapter.lenient();
        }
        return new MoshiRequestBodyConverter<>((JsonAdapter<Document<?>>) adapter, type);
    }

    private static final MediaType MEDIA_TYPE = MediaType.parse("application/json; charset=UTF-8");

    private static class MoshiResponseBodyConverter<R> implements Converter<ResponseBody, R> {
        private final JsonAdapter<Document<?>> adapter;
        private final Class<R> rawType;

        MoshiResponseBodyConverter(JsonAdapter<Document<?>> adapter, Type type) {
            this.adapter = adapter;
            this.rawType = (Class<R>) Types.getRawType(type);
        }

        @Override
        public R convert(ResponseBody value) throws IOException {
            try {
                Document<?> document = adapter.fromJson(value.source());
                if (Document.class.isAssignableFrom(rawType)) {
                    return (R) document;
                } else if (List.class.isAssignableFrom(rawType)) {
                    ArrayDocument arrayDocument = document.asArrayDocument();
                    List a;
                    if (rawType.isAssignableFrom(ArrayList.class)) {
                        a = new ArrayList();
                    } else {
                        a = (List) rawType.newInstance();
                    }
                    a.addAll(arrayDocument);
                    return (R) a;
                } else if (rawType.isArray()) {
                    ArrayDocument<?> arrayDocument = document.asArrayDocument();
                    Object a = Array.newInstance(rawType.getComponentType(), arrayDocument.size());
                    for (int i = 0; i != Array.getLength(a); i++) {
                        Array.set(a, i, arrayDocument.get(i));
                    }
                    return (R) a;
                } else {
                    return (R) document.asObjectDocument().get();
                }
            } catch (InstantiationException e) {
                throw new RuntimeException("Cannot find default constructor of [" + rawType.getCanonicalName() + "].", e);
            } catch (IllegalAccessException e) {
                throw new RuntimeException("Cannot access default constructor of [" + rawType.getCanonicalName() + "].", e);
            } finally {
                value.close();
            }
        }
    }

    private static class MoshiRequestBodyConverter<T> implements Converter<T, RequestBody> {

        private final JsonAdapter<Document<?>> adapter;
        private final Class<T> rawType;

        MoshiRequestBodyConverter(JsonAdapter<Document<?>> adapter, Type type) {
            this.adapter = adapter;
            this.rawType = (Class<T>) Types.getRawType(type);
        }

        @Override
        public RequestBody convert(T value) throws IOException {
            Document document;
            if (Document.class.isAssignableFrom(rawType)) {
                document = (Document) value;
            } else if (List.class.isAssignableFrom(rawType)) {
                ArrayDocument arrayDocument = new ArrayDocument();
                List a = ((List) value);
                if (!a.isEmpty() && a.get(0) != null && ((ResourceIdentifier) a.get(0)).getContext() != null) {
                    arrayDocument = ((ResourceIdentifier) a.get(0)).getContext().asArrayDocument();
                }
                arrayDocument.addAll(a);
                document = arrayDocument;
            } else if (rawType.isArray()) {
                ArrayDocument arrayDocument = new ArrayDocument();
                if (Array.getLength(value) > 0 && ((ResourceIdentifier) Array.get(value, 0)).getContext() != null) {
                    arrayDocument = ((ResourceIdentifier) Array.get(value, 0)).getContext().asArrayDocument();
                }
                for (int i = 0; i != Array.getLength(value); i++) {
                    arrayDocument.add((ResourceIdentifier) Array.get(value, i));
                }
                document = arrayDocument;
            } else {
                ResourceIdentifier data = ((ResourceIdentifier) value);
                ObjectDocument objectDocument = new ObjectDocument();
                if (data.getContext() != null) {
                    objectDocument = data.getContext().asObjectDocument();
                }
                objectDocument.set(data);
                document = objectDocument;
            }
            Buffer buffer = new Buffer();
            adapter.toJson(buffer, document);
            return RequestBody.create(MEDIA_TYPE, buffer.readByteString());
        }
    }

}

Use the converter factory:

Moshi moshi = ...
Retrofit retrofit = new Retrofit.Builder()
        // ...
        .addConverterFactory(JsonApiConverterFactory.create(moshi))
        .build()

The converter automatically adapts all request body and response data which extends Resource class.

public interface MyAPI {

    @GET("posts")
    Call<Post[]> listPosts();

    @GET("posts/{id}")
    Call<Post> getPost(@Path("id") String id);

    @GET("posts/{id}/comments")
    Call<Comment[]> getComments(@Path("id") String id);

    @POST("posts/{id}/comments")
    Call<Document> addComment(@Path("id") String id, @Body Comment comment);

    @DELETE("posts/{id}/relationships/comments")
    Call<Document> removeComments(@Path("id") String id, @Body ResourceIdentifier[] commentIds);

    @GET("posts/{id}/relationships/comments")
    Call<ResourceIdentifier[]> getCommentRels(@Path("id") String id);
}

In the example,

• Supports array and single data, and resource identifier
• All response data have an actual type of Document<T> is adapted into array/data object
• All request body (parameters with @Body annotation) is converted into Document<T>

Is it possible to include resources using this approach?

Same question here: what would be necessary to convert included resources, to automatically resolve relationships?

Okay after some first tests, it seems that included resources are supported. Works fine so far.

This gist is now updated for moshi-jsonapi 3.2.0

@rhlff @tylergets I'm sorry I didn't notice your comment here in the gist. Yes, you can get full feature by using this adapter factory. The adapter factory only wraps/unwrap resource object(s) to/from Document<T> to keep a clean API interface.

This gist is now updated to support List<T extends ResourceIdentifier> in request @Body and response type.

I was wondering why not include "JsonApiConverterFactory.java" into "moshi-jsonapi" package?

Agree with previous comment, this should be included directly in the main package.

I am getting a "java.lang.IllegalArgumentException: Cannot serialize abstract class moe.banana.jsonapi2.Document" when I try to implement this, any reasons that you might think of? Tried to do everything according to guide.

I agree. please add it to the main package

+1 to add it to the main package 👍
I've just lost one day, because of this 🤕

Should line 97 be

    private static final MediaType MEDIA_TYPE = MediaType.parse("application/vnd.api+json; charset=UTF-8");

Instead of

    private static final MediaType MEDIA_TYPE = MediaType.parse("application/json; charset=UTF-8");

This to go along with the specification here http://jsonapi.org/format/#crud-creating

+1 to add it to the main package
and +1 to change according to @pboos

@kaplanf Did you solve the java.lang.IllegalArgumentException? I am having the same problem

DEPRECATION

JsonApiConverterFactory is added to the repository by version 3.5.0 (documentation).

And this snippet is deprecated for the moshi-jsonapi-retrofit-converter library 🙏.

thank you kamikat!