Custom Converter for Retrofit

Question

I am trying to use a custom converter for Retrofit

 RestAdapter.Builder builder = new RestAdapter.Builder()
                .setEndpoint(BuildConfig.BASE_SERVER_ENDPOINT)
                .setClient(new OkClient(client)).setConverter(new CitationResponseConverter())
                .setLogLevel(RestAdapter.LogLevel.FULL);

below is my custom converter

public class CitationResponseConverter implements Converter {

    @Override
    public Object fromBody(TypedInput typedInput, Type type) throws ConversionException {
        try {
            InputStream in = typedInput.in(); // convert the typedInput to String
            String string = fromStream(in);
            in.close(); // we are responsible to close the InputStream after use

            if (String.class.equals(type)) {
                return string;
            } else {
                return new Gson().fromJson(string,
                        type); // convert to the supplied type, typically Object, JsonObject or Map<String, Object>
            }
        } catch (Exception e) { // a lot may happen here, whatever happens
            throw new ConversionException(
                    e); // wrap it into ConversionException so retrofit can process it
        }
    }

    @Override
    public TypedOutput toBody(Object object) {
        return null;
    }

    private static String fromStream(InputStream in) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        StringBuilder out = new StringBuilder();
        String line;
        while ((line = reader.readLine()) != null) {
            out.append(line);
            out.append("\r\n");
        }
        return out.toString();
    }
}

I am getting the following error

retrofit.RetrofitError: method POST must have a request body.

while trying to make this api call

 @POST("/service/citations")
    Observable<CitationMain> getCitations(@Body CitationRequestBody body);

I suppose the converter is overriding the request for the api call, how can I avoid that and pass the request body defined in the retrofit service.

Response :

{
  "citations": [
    {
      "coverdatestart": "2015-05-01",
      "coverimage": [
        "09699961/S0969996115X00040/cov200h.gif",
        "09699961/S0969996115X00040/cov150h.gif"
      ],
      "pubyear": "2015",
      "refimage": [
        "09699961/S0969996115X00040/S0969996115000522/gr1-t.gif",
        "09699961/S0969996115X00040/S0969996115000522/gr1.jpg"
      ],
      "volissue": "Volume 77",
      "volume": "77"
    },
    {
      "pubdatetxt": "19700101",
      "refimage": "mma:otto_4_9781455748600/9781455748600_0020",
    }
  ]
}

Answer 1

I would do something like that:

public class StringList extends ArrayList<String> {
    // Empty on purpose. The class is here only to be recognized by Gson
}

public class CitationMain {
    @SerializedName("field_name_here")
    StringList values;

    // Your other fields
}

Then when creating the RestAdapter:

public class StringListDeserializer implements JsonDeserializer<StringList> {

    @Override
    public StringList deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext
            context) throws JsonParseException {
        StringList value = new StringList();
        if (json.isJsonArray()) {
            for (JsonElement element : json.getAsJsonArray()) {
                value.add(element.getAsString());
            }
        } else {
            value.add(json.getAsString());
        }
        return value;
    }
}

And then:

Gson gson = new GsonBuilder()
            .registerTypeAdapter(StringList.class, new StringListDeserializer())
            .create();

RestAdapter.Builder builder = new RestAdapter.Builder()
            //...
            .setConverter(new GsonConverter(gson));

It's not ideal, since the object is custom, but any other solution that I can think of right now is significantly more complex.

The deserializer here is registered specifically for the fields declared as StringList, and will handle the case of a single string as well as the case of a string array. Any other field type will use the default deserialization process.