You cannot cache POST requests. Only GET requests can be cached. Inside the interceptors, you need to get chain. request() to get the current request and add Cache options to it.
Some image loading library like Picasso or Glide provide this caching when loading and displaying images but retrofit does not use this by default for its requests.
Basically: The client will send out something like timestamp or Etag of the last request. The server can then check if there is some data has changed in during that period of time or not. If nothing has changed, the server can just give a special code (304 -not modified) without sending the whole same response again.
OkHttp is a pure HTTP/SPDY client responsible for any low-level network operations, caching, requests and responses manipulation. In contrast, Retrofit is a high-level REST abstraction build on top of OkHttp. Retrofit is strongly coupled with OkHttp and makes intensive use of it.
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 cache
File httpCacheDirectory = new File(context.getCacheDir(), "responses");
int cacheSize = 10 * 1024 * 1024; // 10 MiB
Cache cache = new Cache(httpCacheDirectory, cacheSize);
//add cache to the client
client.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.
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);
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();
}
The answer is YES, based on the above answers, I started writing unit tests to verify all possible use cases :
I built a small helper lib to configure OKHttp cache easily, you can see the related unittest here on Github : https://github.com/ncornette/OkCacheControl/blob/master/okcache-control/src/test/java/com/ncornette/cache/OkCacheControlTest.java
Unittest that demonstrates the use of cache when offline :
@Test
public void test_USE_CACHE_WHEN_OFFLINE() throws Exception {
//given
givenResponseInCache("Expired Response in cache", -5, MINUTES);
given(networkMonitor.isOnline()).willReturn(false);
//when
//This response is only used to not block when test fails
mockWebServer.enqueue(new MockResponse().setResponseCode(404));
Response response = getResponse();
//then
then(response.body().string()).isEqualTo("Expired Response in cache");
then(cache.hitCount()).isEqualTo(1);
}
As you can see, cache can be used even if it has expired. Hope it will help.
building on @kosiara-bartosz-kasarzycki's answer, I created a sample project that properly loads from memory->disk->network using retrofit, okhttp, rxjava and guava. https://github.com/digitalbuddha/StoreDemo
Cache with Retrofit2 and OkHTTP3:
OkHttpClient client = new OkHttpClient
.Builder()
.cache(new Cache(App.sApp.getCacheDir(), 10 * 1024 * 1024)) // 10 MB
.addInterceptor(new Interceptor() {
@Override public Response intercept(Chain chain) throws IOException {
Request request = chain.request();
if (NetworkUtils.isNetworkAvailable()) {
request = request.newBuilder().header("Cache-Control", "public, max-age=" + 60).build();
} else {
request = request.newBuilder().header("Cache-Control", "public, only-if-cached, max-stale=" + 60 * 60 * 24 * 7).build();
}
return chain.proceed(request);
}
})
.build();
NetworkUtils.isNetworkAvailable() static method:
public static boolean isNetworkAvailable(Context context) {
ConnectivityManager cm =
(ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeNetwork = cm.getActiveNetworkInfo();
return activeNetwork != null &&
activeNetwork.isConnectedOrConnecting();
}
Then just add client to the retrofit builder:
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(BASE_URL)
.client(client)
.addConverterFactory(GsonConverterFactory.create())
.build();
Original source: https://newfivefour.com/android-retrofit2-okhttp3-cache-network-request-offline.html
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