Droidcon NYC 2014 Retrofit Demo

This sample project demonstrates Retrofit implementations for the Foursquare and Reddit APIs.

Foursquare

The Foursquare demo is a rather straightforward retrofit implementation. The documentation for the venues endpoint can be found here.

You can find the Foursquare models [here] (app/src/main/java/com/timehop/droidcon2014retrofitsample/data/foursquare/model), and the Retrofit service interface in [FoursquareService.java] (app/src/main/java/com/timehop/droidcon2014retrofitsample/data/foursquare/FoursquareService.java).

These models implement a strict pattern of defining the JSON field names in constants at the top of the file because our [legacy async task implementation] (app/src/main/java/com/timehop/droidcon2014retrofitsample/data/foursquare/legacy/VenueSearchTask.java) does not benefit from the @SerializedName annotation, an in order to maintain refactorability, the JSON field names must be defined separately.

The 4sq service interface also has a nested class called FoursquareService.Implementation which can be used to access the default implementation of the service like this:

FoursquareService.Implementation.get()

With an instance of the service, you may call any methods defined in the FoursquareService interface, like so:

FoursquareService.Implementation.get().searchVenues("New York");

To view the API in action, either look at the [tests] (app/src/androidTest/java/com/timehop/droidcon2014retrofitsample/data/foursquare/FoursquareTests.java) or [sample activity] (app/src/main/java/com/timehop/droidcon2014retrofitsample/VenueSearchActivity.java).

Reddit

The reddit demo is a bit more complex since reddit returns dynamically-typed JSON.

The API documentation for reddit is available here. The important thing to take out of this is that reddit 'things' are typed as follows:

• t1: Comment
• t2: Account
• t3: Link
• t4: Message
• t5: Subreddit
• t6: Award
• t8: PromoCampaign

The reddit models in this sample can be found [here] (/app/src/main/java/com/timehop/droidcon2014retrofitsample/data/reddit/model) and the Retrofit API interface can be found [here] (/app/src/main/java/com/timehop/droidcon2014retrofitsample/data/reddit/RedditService.java).

The challenge is to instruct GSON through the use of a type adapter how to instantiate the correct subclass of RedditObject at runtime.

This is achieved through the [RedditObjectDeserializer] (app/src/main/java/com/timehop/droidcon2014retrofitsample/data/reddit/RedditObjectDeserializer.java) with the help of the [RedditType enumeration] (app/src/main/java/com/timehop/droidcon2014retrofitsample/data/reddit/RedditType.java).

The [RedditType enum] (app/src/main/java/com/timehop/droidcon2014retrofitsample/data/reddit/RedditType.java) maps the types defined in reddit documentation to the Java classes that model them.

The [RedditObjectDeserializer] (app/src/main/java/com/timehop/droidcon2014retrofitsample/data/reddit/RedditObjectDeserializer.java) first examines the wrapped JSON objects that look like this:

{
  "kind": "t1",
  "data": { ... }
}

and convert them into a [RedditObjectWrapper] (app/src/main/java/com/timehop/droidcon2014retrofitsample/data/reddit/model/RedditObjectWrapper.java) that looks like this:

public class RedditObjectWrapper {
  RedditType kind;
  JsonElement data;
}

Then, [RedditObjectDeserializer] (app/src/main/java/com/timehop/droidcon2014retrofitsample/data/reddit/RedditObjectDeserializer.java) passes the wrapped json correct derived class into the existing deserialization context to create the correct model.

RedditObjectWrapper wrapper = new Gson().fromJson(json, RedditObjectWrapper.class);
      return context.deserialize(wrapper.data, wrapper.kind.getDerivedClass());

Persisting Cookies

Check out this gist for an easy way to persist cookies.