RestClient.java

package com.verdad.core;

import android.content.Context;

import com.google.gson.FieldNamingPolicy;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

import java.util.HashMap;
import java.util.Map;

import retrofit.RequestInterceptor;
import retrofit.RestAdapter;
import retrofit.converter.GsonConverter;

public class RestClient {

    private final String TAG = this.getClass().getSimpleName();
    private static RestClient instance;

    private RestAdapter mRestAdapter;

    // creating a kind of cache for using different clients
    private Map<String, Object> mClients = new HashMap<String, Object>();

    // singleton pattern
    public static RestClient getInstance() {
        if (null == instance) {
            instance = new RestClient();
        }
        return instance;
    }

    // used on Application.OnCreate() to initialize the service
    public void configureRestAdapter(final Context context, String baseServerPath, RequestInterceptor interceptor ) {
        Gson gson = new GsonBuilder()
                .setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
                .create();

        mRestAdapter = new RestAdapter.Builder()
                .setEndpoint(baseServerPath)
                .setConverter(new GsonConverter(gson))
                .setLogLevel(RestAdapter.LogLevel.FULL)
                .setRequestInterceptor(interceptor)
                .build();
    }

    @SuppressWarnings("unchecked")
    public <T> T getClient(Class<T> clazz) {

        // guard for uninitialized mRestAdapter
        if (mRestAdapter == null) {
            return null;
        }

        // initializing generic client
        T client = null;

        // check service cache for client
        if ((client = (T) mClients.get(clazz.getCanonicalName())) != null) {
            return client;
        }

        // create a new client and save it in cache
        client = mRestAdapter.create(clazz);
        mClients.put(clazz.getCanonicalName(), client);
        return client;
    }

}

VedadApplication.java

package com.ringseven.verdad.domain;

import android.app.Application;
import android.content.SharedPreferences;

import com.ringseven.verdad.core.RestClient;
import com.ringseven.verdad.core.helpers.EncryptionHelper;
import com.ringseven.verdad.core.helpers.UserAgentHelper;
import com.ringseven.verdad.domain.Constants;

import retrofit.RequestInterceptor;
import se.simbio.encryption.Encryption;

import static com.ringseven.verdad.domain.Constants.Prefs.TOKEN;
import static com.ringseven.verdad.domain.Constants.SHARED_PREFS;

/**
 * Created by samgubler on 4/30/15.
 */
public class VerdadApplication extends Application {

    private Session session;

    @Override
    public void onCreate() {
        super.onCreate();

        initializeRestClient();

        // Prime the encryption helper
        EncryptionHelper.primeInstance(Constants.IV);
    }

    private void initializeRestClient() {
        RestClient.getInstance().configureRestAdapter(this, Constants.MOCK_API_URL_STRING, new RequestInterceptor() {
            @Override
            public void intercept(RequestFacade request) {
                request.addHeader("App-User-Agent", UserAgentHelper.agentString(getApplicationContext()));
                request.addHeader(("Content-Type"), "application/json");
            }
        });
    }

    public Session getSession() {
        if (session == null) {
            session = new Session();
        }
        return session;
    }

}