Can Retrofit with OKHttp use cache data when offline

Edit for Retrofit 2.x:

OkHttp Interceptor is the right way to access cache when offline:

1) Create Interceptor:

private static final Interceptor REWRITE_CACHE_CONTROL_INTERCEPTOR = new Interceptor() {    @Override public Response intercept(Chain chain) throws IOException {        Response originalResponse = chain.proceed(chain.request());        if (Utils.isNetworkAvailable(context)) {            int maxAge = 60; // read from cache for 1 minute            return originalResponse.newBuilder()                    .header("Cache-Control", "public, max-age=" + maxAge)                    .build();        } else {            int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale            return originalResponse.newBuilder()                    .header("Cache-Control", "public, only-if-cached, max-stale=" + maxStale)                    .build();        }    }

2) Setup client:

OkHttpClient client = new OkHttpClient();client.networkInterceptors().add(REWRITE_CACHE_CONTROL_INTERCEPTOR);//setup cacheFile httpCacheDirectory = new File(context.getCacheDir(), "responses");int cacheSize = 10 * 1024 * 1024; // 10 MiBCache cache = new Cache(httpCacheDirectory, cacheSize);//add cache to the clientclient.setCache(cache);

3) Add client to retrofit

Retrofit retrofit = new Retrofit.Builder()        .baseUrl(BASE_URL)        .client(client)        .addConverterFactory(GsonConverterFactory.create())        .build();

Also check @kosiara - Bartosz Kosarzycki's answer. You may need to remove some header from the response.

OKHttp 2.0.x (Check the original answer):

Since OKHttp 2.0.x HttpResponseCache is Cache, setResponseCache is setCache. So you should setCache like this:

        File httpCacheDirectory = new File(context.getCacheDir(), "responses");        Cache cache = null;        try {            cache = new Cache(httpCacheDirectory, 10 * 1024 * 1024);        } catch (IOException e) {            Log.e("OKHttp", "Could not create http cache", e);        }        OkHttpClient okHttpClient = new OkHttpClient();        if (cache != null) {            okHttpClient.setCache(cache);        }        String hostURL = context.getString(R.string.host_url);        api = new RestAdapter.Builder()                .setEndpoint(hostURL)                .setClient(new OkClient(okHttpClient))                .setRequestInterceptor(/*rest of the answer here */)                .build()                .create(MyApi.class);

Original Answer:

It turns out that server response must have Cache-Control: public to make OkClient to read from cache.

Also If you want to request from network when available, you should add Cache-Control: max-age=0 request header. This answer shows how to do it parameterized. This is how I used it:

RestAdapter.Builder builder= new RestAdapter.Builder()   .setRequestInterceptor(new RequestInterceptor() {        @Override        public void intercept(RequestFacade request) {            request.addHeader("Accept", "application/json;versions=1");            if (MyApplicationUtils.isNetworkAvailable(context)) {                int maxAge = 60; // read from cache for 1 minute                request.addHeader("Cache-Control", "public, max-age=" + maxAge);            } else {                int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale                request.addHeader("Cache-Control",                     "public, only-if-cached, max-stale=" + maxStale);            }        }});

All of the anwsers above did not work for me. I tried to implement offline cache in retrofit 2.0.0-beta2. I added an interceptor using okHttpClient.networkInterceptors() method but received java.net.UnknownHostException when I tried to use the cache offline. It turned out that I had to add okHttpClient.interceptors() as well.

The problem was that cache wasn't written to flash storage because the server returned Pragma:no-cache which prevents OkHttp from storing the response. Offline cache didn't work even after modifying request header values. After some trial-and-error I got the cache to work without modifying the backend side by removing pragma from reponse instead of the request - response.newBuilder().removeHeader("Pragma");

Retrofit: 2.0.0-beta2; OkHttp: 2.5.0

OkHttpClient okHttpClient = createCachedClient(context);Retrofit retrofit = new Retrofit.Builder()        .client(okHttpClient)        .baseUrl(API_URL)        .addConverterFactory(GsonConverterFactory.create())        .build();service = retrofit.create(RestDataResource.class);

...

private OkHttpClient createCachedClient(final Context context) {    File httpCacheDirectory = new File(context.getCacheDir(), "cache_file");    Cache cache = new Cache(httpCacheDirectory, 20 * 1024 * 1024);    OkHttpClient okHttpClient = new OkHttpClient();    okHttpClient.setCache(cache);    okHttpClient.interceptors().add(            new Interceptor() {                @Override                public Response intercept(Chain chain) throws IOException {                    Request originalRequest = chain.request();                    String cacheHeaderValue = isOnline(context)                         ? "public, max-age=2419200"                         : "public, only-if-cached, max-stale=2419200" ;                    Request request = originalRequest.newBuilder().build();                    Response response = chain.proceed(request);                    return response.newBuilder()                        .removeHeader("Pragma")                        .removeHeader("Cache-Control")                        .header("Cache-Control", cacheHeaderValue)                        .build();                }            }    );    okHttpClient.networkInterceptors().add(            new Interceptor() {                @Override                public Response intercept(Chain chain) throws IOException {                    Request originalRequest = chain.request();                    String cacheHeaderValue = isOnline(context)                         ? "public, max-age=2419200"                         : "public, only-if-cached, max-stale=2419200" ;                    Request request = originalRequest.newBuilder().build();                    Response response = chain.proceed(request);                    return response.newBuilder()                        .removeHeader("Pragma")                        .removeHeader("Cache-Control")                        .header("Cache-Control", cacheHeaderValue)                        .build();                }            }    );    return okHttpClient;}

...

public interface RestDataResource {    @GET("rest-data")     Call<List<RestItem>> getRestData();}

My solution:

private BackendService() {    httpCacheDirectory = new File(context.getCacheDir(),  "responses");    int cacheSize = 10 * 1024 * 1024; // 10 MiB    Cache cache = new Cache(httpCacheDirectory, cacheSize);    httpClient = new OkHttpClient.Builder()            .addNetworkInterceptor(REWRITE_RESPONSE_INTERCEPTOR)            .addInterceptor(OFFLINE_INTERCEPTOR)            .cache(cache)            .build();    Retrofit retrofit = new Retrofit.Builder()            .baseUrl("https://api.backend.com")            .client(httpClient)            .addConverterFactory(GsonConverterFactory.create())            .build();    backendApi = retrofit.create(BackendApi.class);}private static final Interceptor REWRITE_RESPONSE_INTERCEPTOR = chain -> {    Response originalResponse = chain.proceed(chain.request());    String cacheControl = originalResponse.header("Cache-Control");    if (cacheControl == null || cacheControl.contains("no-store") || cacheControl.contains("no-cache") ||            cacheControl.contains("must-revalidate") || cacheControl.contains("max-age=0")) {        return originalResponse.newBuilder()                .header("Cache-Control", "public, max-age=" + 10)                .build();    } else {        return originalResponse;    }};private static final Interceptor OFFLINE_INTERCEPTOR = chain -> {    Request request = chain.request();    if (!isOnline()) {        Log.d(TAG, "rewriting request");        int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale        request = request.newBuilder()                .header("Cache-Control", "public, only-if-cached, max-stale=" + maxStale)                .build();    }    return chain.proceed(request);};public static boolean isOnline() {    ConnectivityManager cm = (ConnectivityManager) MyApplication.getApplication().getSystemService(Context.CONNECTIVITY_SERVICE);    NetworkInfo netInfo = cm.getActiveNetworkInfo();    return netInfo != null && netInfo.isConnectedOrConnecting();}