How to use interceptor to add Headers in Android Retrofit

In this android programming source code example, we are going to use interceptor to add Headers in Android Retrofit.

You can copy and adopt this source code example to your android project without reinventing the wheel.

Below is a step by step source code to use interceptor to add Headers in Android Retrofit.

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/list"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</RelativeLayout>

MainActivity.java

import android.app.ProgressDialog;
import android.content.Context;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.DividerItemDecoration;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;
import com.google.gson.annotations.SerializedName;

import java.io.IOException;
import java.util.List;
import java.util.concurrent.TimeUnit;

import okhttp3.Interceptor;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;
import retrofit2.http.GET;

public class RetrofitActivity11 extends AppCompatActivity {
    private RecyclerView list;
    private ProgressDialog progressDialog;
    private String baseUrl;
    private List<RetrofitGetResponse> responseList;
    private adapter recyclerAdapter;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_retrofit11);
        list = (RecyclerView)findViewById(R.id.list);
        baseUrl = "http://dummy.restapiexample.com/";
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        list.setLayoutManager(layoutManager);
        recyclerAdapter = new adapter(RetrofitActivity11.this, responseList);
        list.addItemDecoration(new DividerItemDecoration(RetrofitActivity11.this, DividerItemDecoration.VERTICAL));
        list.setAdapter(recyclerAdapter);
        fetchData();
    }

    private void fetchData(){
        progressDialog = new ProgressDialog(RetrofitActivity11.this);
        progressDialog.setMessage(getString(R.string.loading));
        progressDialog.setCancelable(false);
        progressDialog.show();
        //Defining retrofit api service
        OkHttpClient client = new OkHttpClient.Builder()
                .connectTimeout(60, TimeUnit.SECONDS)
                .writeTimeout(60, TimeUnit.SECONDS)
                .readTimeout(60, TimeUnit.SECONDS)
                .addInterceptor( HeaderInterceptor() )
                .build();
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(baseUrl)
                .addConverterFactory(GsonConverterFactory.create())
                .client(client)
                .build();


        ApiService service = retrofit.create(ApiService.class);
        Call<List<RetrofitGetResponse>> call = service.GetEmployeeData();
        //calling the api
        call.enqueue(new Callback<List<RetrofitGetResponse>>() {
            @Override
            public void onResponse(Call<List<RetrofitGetResponse>> call, Response<List<RetrofitGetResponse>> response) {
                //hiding progress dialog
                progressDialog.dismiss();
                //if there is no error
                responseList = response.body();
                recyclerAdapter.setEmployeeList(responseList);
            }

            @Override
            public void onFailure(Call<List<RetrofitGetResponse>> call, Throwable t) {
                progressDialog.dismiss();
                Toast.makeText(getApplicationContext(), t.getMessage(), Toast.LENGTH_LONG).show();
            }
        });

    }

    public Interceptor HeaderInterceptor() {
        return new Interceptor() {
        @Override
        public okhttp3.Response intercept(Chain chain) throws IOException {
            okhttp3.Request request = chain.request();
            request = request.newBuilder()
                    .addHeader("Content-Type", "application/json")
                    .build();
            okhttp3.Response response = chain.proceed(request);
            return response;
        }
        };
    }

    private class adapter extends RecyclerView.Adapter<adapter.myViewHolder> {
        Context context;
        List<RetrofitGetResponse> responseList;

        public adapter(Context context, List<RetrofitGetResponse> data) {
            this.context = context;
            this.responseList = data;
        }

        public void setEmployeeList(List<RetrofitGetResponse> resList) {
            this.responseList = resList;
            notifyDataSetChanged();
        }

        @Override
        public adapter.myViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(context).inflate(R.layout.retrofit_adapter1, parent, false);
            return new myViewHolder(view);
        }

        @Override
        public void onBindViewHolder(adapter.myViewHolder holder, int position) {
            holder.name.setText(responseList.get(position).getEmployeeName());
            holder.salary.setText(responseList.get(position).getEmployeeSalary());
            holder.age.setText(responseList.get(position).getEmployeeAge());
        }

        @Override
        public int getItemCount() {
            if(responseList != null){
                return responseList.size();
            }
            return 0;

        }

        public class myViewHolder extends RecyclerView.ViewHolder {
            TextView name;
            TextView salary;
            TextView age;

            public myViewHolder(View itemView) {
                super(itemView);
                name = (TextView) itemView.findViewById(R.id.Name);
                salary = (TextView) itemView.findViewById(R.id.Salary);
                age = (TextView) itemView.findViewById(R.id.Age);
            }
        }
    }

    private interface ApiService {
        @GET("api/v1/employees")
        Call<List<RetrofitGetResponse>> GetEmployeeData();
    }

    private class RetrofitGetResponse{
        @SerializedName("profile_image")
        private String profileImage;
        @SerializedName("employee_name")
        private String employeeName;
        @SerializedName("employee_salary")
        private String employeeSalary;
        @SerializedName("id")
        private String id;
        @SerializedName("employee_age")
        private String employeeAge;

        public void setProfileImage(String profileImage){
            this.profileImage = profileImage;
        }
        public String getProfileImage(){
            return profileImage;
        }
        public void setEmployeeName(String employeeName){
            this.employeeName = employeeName;
        }
        public String getEmployeeName(){
            return employeeName;
        }
        public void setEmployeeSalary(String employeeSalary){
            this.employeeSalary = employeeSalary;
        }
        public String getEmployeeSalary(){
            return employeeSalary;
        }
        public void setId(String id){
            this.id = id;
        }
        public String getId(){
            return id;
        }
        public void setEmployeeAge(String employeeAge){
            this.employeeAge = employeeAge;
        }
        public String getEmployeeAge(){
            return employeeAge;
        }
    }
}

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