How to send a JSON object over Request with Android?

In Android development, sending JSON objects is a common method for communicating with network servers. Here, I will demonstrate how to use a popular HTTP library—Retrofit—to implement sending JSON objects.

Sending JSON Objects with Retrofit

1. Add dependencies: First, to use Retrofit, you need to add the Retrofit dependency to your Android project's build.gradle file.

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

   Here, the converter-gson dependency is also added because we need to use GSON for handling JSON.

2. Create a Java interface: Create an interface to define HTTP requests. Suppose we need to send a JSON object to create a new user:

   java
   import retrofit2.Call;
   import retrofit2.http.Body;
   import retrofit2.http.POST;
   
   public interface ApiService {
       @POST("users/new")
       Call<UserResponse> createUser(@Body User user);
   }

   Here, the @Body annotation indicates that the entire User object is sent as the request body.

3. Define POJO classes: Define a simple POJO class to represent the user and response. For example:

   java
   public class User {
       private String name;
       private int age;
   
       // Constructors, getters, and setters
   }
   
   public class UserResponse {
       private boolean success;
       private String message;
   
       // Constructors, getters, and setters
   }

4. Create Retrofit instance and send request: Next, you need to create a Retrofit instance and use it to send requests.

   java
   import retrofit2.Retrofit;
   import retrofit2.converter.gson.GsonConverterFactory;
   
   public class RetrofitClient {
       private static Retrofit retrofit = null;
   
       public static Retrofit getClient(String baseUrl) {
           if (retrofit == null) {
               retrofit = new Retrofit.Builder()
                   .baseUrl(baseUrl)
                   .addConverterFactory(GsonConverterFactory.create())
                   .build();
           }
           return retrofit;
       }
   }

   Then use this client to send requests:

   java
   Retrofit retrofit = RetrofitClient.getClient("https://api.example.com/");
   ApiService service = retrofit.create(ApiService.class);
   
   User newUser = new User("Zhang San", 25);
   Call<UserResponse> call = service.createUser(newUser);
   call.enqueue(new Callback<UserResponse>() {
       @Override
       public void onResponse(Call<UserResponse> call, Response<UserResponse> response) {
           if (response.isSuccessful()) {
               Log.d("TAG", "onResponse: Success");
           } else {
               Log.d("TAG", "onResponse: Error " + response.code());
           }
       }
   
       @Override
       public void onFailure(Call<UserResponse> call, Throwable t) {
           Log.e("TAG", "onFailure: " + t.getMessage());
       }
   });

Summary

Through the above steps, you can use the Retrofit library in your Android project to send JSON objects. This method not only has a clear code structure but also, through Retrofit's encapsulation, makes network requests more concise and easier to manage.