Create API using Retrofit2, Okhttp3 and Gson (Java)

A memorandum when creating the API. I was able to communicate with this for the time being, without detailed explanation.

• Retrofit2
• Okhttp3
• Gson

procedure

--Set manifestfile to allow communication --Define a class for receiving requests and responses --Create endpoint --Create HTTP client --Execute

Set manifestFile to allow communication

AndroidManifest.Write the following in xml

#### **`AndroidManifest.xml`**
```java

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

Define a class for receiving requests and responses

Request class for login, body of request is sent in this format

LoginRequest.java

package com.example.bookmanager_android.models.requests;

public class LoginRequest {
    private String email;
    private String password;

    public LoginRequest(String email, String passWord){
        this.email = email;
        this.password = passWord;
    }
}

--Response class

Response class for login, response is received in this form

LoginResponse.java

package com.example.bookmanager_android.models.requests.response;

public class LoginResponse {
    public int status;
    public Result result;

    public static class Result {
        public int id;
        public String email;
        public String token;
    }
}

Create an endpoint

Create interface

RequestApiService

public interface RequestApiService {
    @POST("/login") //API endpoint
    Call<LoginResponse> logIn(@Body LoginRequest requestBody); 
    //When the logIn method is called,The body format will be the form of the LoginRequest class created above.
}

Creating an HTTP client

HttpClient.java

public class HttpClient {
    public static RequestApiService apiService;

    private static final String URL = "http://baseurl"; //Specify BaseUrl

    // Okhttp
    private static final OkHttpClient client = new OkHttpClient.Builder()
            .connectTimeout(10, TimeUnit.SECONDS)
            .writeTimeout(10, TimeUnit.SECONDS)
            .readTimeout(30, TimeUnit.SECONDS)
            .build();
    // GSON
    private static final Gson gson = new GsonBuilder()
            .setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
            .create();

    //Create an Http client by combining Retrofit with GSON and Okhttp
    public static RequestApiService getRequestApiService() {
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(URL)
                .addConverterFactory(GsonConverterFactory.create(gson))
                .client(client)
                .build();
        apiService = retrofit.create(RequestApiService.class);
        return apiService;
    }

Run

SignInFragment.java

private boolean starLogin(String emailStr, String passwordStr) {
        //Creating a body
        LoginRequest requestBody = new LoginRequest(emailStr, passwordStr);
        //HTTP client call
        RequestApiService apiService = HttpClient.getRequestApiService();

        //Communication start: The process defined in interface is called
        apiService.logIn(requestBody).enqueue(new Callback<LoginResponse>() {
            @Override
            public void onResponse(Call<LoginResponse> call, Response<LoginResponse> response) {
                if (response.isSuccessful()) {
                   //Describes the processing when communication processing is successful
                } else {
                    Log.e("SignInFragment", "Something wrong On Response: " + response.toString());   
                }
            }

            @Override
            public void onFailure(Call<LoginResponse> call, Throwable t) {
                //Describes the processing when communication processing fails
            }
        });
        return true;
    }

Impressions

There are still things like holding tokens and processing when success or failure occurs, but for the time being, communication was possible.