Two weeks ago i wrote an Android app with connection to a REST-API. As yet i used Volley for requests. But i finally took a look at Retrofit and i think i like it. In this post i want to give a short introduction on how to use it.
What is Retrofit?
Retrofit is type-safe HTTP client for Android and Java by Square, Inc.
You can use it to simplify your API calls.
1) Create Project
Add internet permission to your AndroidManifest.xml:
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<uses-permission android:name="android.permission.INTERNET"> |
Add Retrofit in your build.gradle:
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dependencies { compile 'com.squareup.retrofit2:retrofit:2.1.0' compile 'com.google.code.gson:gson:2.6.2' compile 'com.squareup.retrofit2:converter-gson:2.0.2' } |
In this example i will use Gson for JSON deserialization.
2) Create a new interface
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public interface SampleRetrofitInterface { @GET("/posts") Call<List<Post>> getPostList(); @GET("/posts/{id}") Call<Post> getSinglePost(@Path("id") int postId); @GET("/posts/") Call<Post> getSinglePostQuery(@Query("userId") int userId); @PUT("/posts/{id}") Call<Post> putSinglePost(@Path("id") int postId); @DELETE("/posts/{id}") Call<String> deletePost(@Path("id") int postId); @POST("users/new") Call<Post> createPost(@Body Post post); Retrofit retrofit = new Retrofit.Builder() .addConverterFactory(GsonConverterFactory.create()) .baseUrl("https://jsonplaceholder.typicode.com") .build(); } |
In this example the baseUrl is “https://jsonplaceholder.typicode.com/”
With the annotations you can set the standard HTTP methods like (GET, POST, PUT, DELETE, PATCH, and HEAD).
For example when you call getSinglePostQuery(3) Retrofit will connect to https://jsonplaceholder.typicode.com/posts?userId=3
When you call getSinglePost(3) it will be https://jsonplaceholder.typicode.com/posts/3
3) Create Java class for parsing
This is how a typical response from https://jsonplaceholder.typicode.com/posts looks like.
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[ { "userId": 1, "id": 1, "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit", "body": "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto" }, { "userId": 1, "id": 2, "title": "qui est esse", "body": "est rerum tempore vitae\nsequi sint nihil reprehenderit dolor beatae ea dolores neque\nfugiat blanditiis voluptate porro vel nihil molestiae ut reiciendis\nqui aperiam non debitis possimus qui neque nisi nulla" } ] |
And this is my class that Gson will use to create objects from the JSON response:
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public class Post { int userId; int id; String title; String body; public Post(int userId, int id, String title, String body) { this.userId = userId; this.id = id; this.title = title; this.body = body; } public int getUserId() { return userId; } public int getId() { return id; } public String getTitle() { return title; } public String getBody() { return body; } } |
4) Use the interface
Now you can use the methods from your network interface anywhere you want.
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SampleRetrofitInterface api = SampleRetrofitInterface.retrofit.create(SampleRetrofitInterface.class); Call<List<Post>> call = api.getPostList(); call.enqueue(new Callback<List<Post>>() { @Override public void onResponse(Call<List<Post>>call, Response<List<Post>> response) { Log.i("INFO", String.valueOf(response.body().size())); } @Override public void onFailure(Call<List<Post>>call, Throwable t) { // Log error here since request failed } }); |
The Response in onResponse will return a List of Posts.
I think Retrofit is a easy way to connect to an REST-API.
Example Project
You can find my example project on GitHub
BTW: I used a similar library (Refit) in a Xamarin Project
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