NetworkUtils.java

import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
public class NetworkUtils {
    /**
     * 获取活动网路信息
     *
     * @param context 上下文
     * @return NetworkInfo
     */
    private static NetworkInfo getActiveNetworkInfo(Context context) {
        ConnectivityManager cm = (ConnectivityManager) context
                .getSystemService(Context.CONNECTIVITY_SERVICE);
        return cm.getActiveNetworkInfo();
    }
    /**
     * 判断网络是否可用
     * <p>需添加权限 android.permission.ACCESS_NETWORK_STATE</p>
     */
    public static boolean isAvailable(Context context) {
        NetworkInfo info = getActiveNetworkInfo(context);
        return info != null && info.isAvailable();
    }

}

RetrofitApplication.java

import android.app.Application;
import android.content.Context;
public class RetrofitApplication extends Application {
    private static RetrofitApplication application;

    @Override
    public void onCreate() {
        super.onCreate();
        application = this;
    }

    private RetrofitApplication getApplication(){
        return application;
    }
    public static Context getContext(){
        return  application.getApplicationContext();
    }

}

RetrofitManager.java

import com.jakewharton.retrofit2.adapter.rxjava2.RxJava2CallAdapterFactory;
import java.io.File;
import java.io.IOException;
import java.util.concurrent.TimeUnit;
import okhttp3.Cache;
import okhttp3.CacheControl;
import okhttp3.Interceptor;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
import okhttp3.logging.HttpLoggingInterceptor;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;
public class RetrofitManager {
    private static final String CACHE_NAME  = "retrofitcache";
    private static Retrofit retrofit = null;
    private static String url = "";
    public static Retrofit getInstance(String baseUrl) {
        url = baseUrl;
        if (retrofit == null) {
            return create();
        } else {
            return retrofit;
        }
    }

    private static Retrofit create() {
        OkHttpClient.Builder builder = new OkHttpClient.Builder();
        // log用拦截器
        HttpLoggingInterceptor loggingInterceptor = new HttpLoggingInterceptor();
        // 开发模式记录整个body，否则只记录基本信息如返回200，http协议版本等
        if (BuildConfig.DEBUG) {
            loggingInterceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
        } else {
            loggingInterceptor.setLevel(HttpLoggingInterceptor.Level.BASIC);
        }

        //设置缓存目录
        File cacheFile = new File(RetrofitApplication.getContext().getExternalCacheDir(), CACHE_NAME);
        //生成缓存，50M
        Cache cache = new Cache(cacheFile, 1024 * 1024 * 50);
        //缓存拦截器
        Interceptor cacheInterceptor = new Interceptor() {
            @Override
            public Response intercept(Chain chain) throws IOException {
                Request request = chain.request();
                //网络不可用
                if (!NetworkUtils.isAvailable(RetrofitApplication.getContext())) {
                    //在请求头中加入：强制使用缓存，不访问网络
                    request = request.newBuilder()
                            .cacheControl(CacheControl.FORCE_CACHE)
                            .build();
                }
                Response response = chain.proceed(request);
                //网络可用
                if (NetworkUtils.isAvailable(RetrofitApplication.getContext())) {
                    int maxAge = 0;
                    // 有网络时 在响应头中加入：设置缓存超时时间0个小时
                    response.newBuilder()
                            .header("Cache-Control", "public, max-age=" + maxAge)
                            .removeHeader("pragma")
                            .build();
                } else {
                    // 无网络时，在响应头中加入：设置超时为4周
                    int maxStale = 60 * 60 * 24 * 28;
                    response.newBuilder()
                            .header("Cache-Control", "public, only-if-cached, max-stale=" + maxStale)
                            .removeHeader("pragma")
                            .build();
                }
                return response;
            }
        };
        builder.addInterceptor(loggingInterceptor)
        .addInterceptor(cacheInterceptor)
        .cache(cache)
        .connectTimeout(15, TimeUnit.SECONDS)//设置超时
        .readTimeout(20, TimeUnit.SECONDS)
        .writeTimeout(20, TimeUnit.SECONDS)
        .retryOnConnectionFailure(true);//错误重连
        OkHttpClient client = builder.build();
        retrofit = new Retrofit.Builder()
                .baseUrl(url)
                //设置 Json 转换器
                .addConverterFactory(GsonConverterFactory.create())
                //RxJava 适配器
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .client(client)
                .build();
        return retrofit;
    }
}