REST API Integration in Android using Retrofit

In this tutorial, you will learn how to integrate REST APIs in Android using Retrofit. Retrofit is a powerful HTTP client for making network requests and handling JSON data easily.

What is Retrofit?

Retrofit is a type-safe HTTP client for Android that simplifies API calls and converts JSON responses into Java/Kotlin objects.

Features of Retrofit

• Easy API integration
• Supports GET, POST, PUT, DELETE
• Automatic JSON parsing
• Works with Gson, Moshi
• Supports asynchronous calls

Add Dependencies

implementation 'com.squareup.retrofit2:retrofit:2.9.0'
implementation 'com.squareup.retrofit2:converter-gson:2.9.0'

Create API Interface

public interface ApiService {
    @GET("posts")
    Call<List<Post>> getPosts();
}

Create Model Class

public class Post {
    private int id;
    private String title;

    public int getId() { return id; }
    public String getTitle() { return title; }
}

Create Retrofit Instance

Retrofit retrofit = new Retrofit.Builder()
    .baseUrl("https://jsonplaceholder.typicode.com/")
    .addConverterFactory(GsonConverterFactory.create())
    .build();

ApiService api = retrofit.create(ApiService.class);

Make API Request

api.getPosts().enqueue(new Callback<List<Post>>() {
    @Override
    public void onResponse(Call<List<Post>> call, Response<List<Post>> response) {
        if(response.isSuccessful()) {
            List<Post> posts = response.body();
        }
    }

    @Override
    public void onFailure(Call<List<Post>> call, Throwable t) {
        t.printStackTrace();
    }
});

POST Request Example

@POST("posts")
Call<Post> createPost(@Body Post post);

Permissions

<uses-permission android:name="android.permission.INTERNET" />

Enhancements

• Use RecyclerView to display API data
• Add loading indicators
• Handle errors properly
• Use MVVM architecture
• Use Coroutines (Kotlin)

Common Mistakes

• Missing INTERNET permission
• Wrong base URL
• Not handling null responses
• Blocking main thread
• Incorrect JSON mapping

Practice Exercises

• Display API data in RecyclerView
• Create POST request form
• Add loading spinner
• Handle API errors
• Convert project to Kotlin

Conclusion

Retrofit makes API integration simple and efficient in Android apps. Mastering it allows you to connect your app with real-world data and services.