如何使用 OkHttp/Afterfit 重试 HTTP 请求？

I don't know if this is an option for you but you could use RxJava together with Retrofit.

Retrofit is able to return Observables upon rest calls. On Oberservables you can just call retry(count) to resubscribe to the Observable when it emits an error.

You would have to define the call in your interface like this:

@GET("/data.json")
Observable<DataResponse> fetchSomeData();

Then you can subscribe to this Observable like this:

restApi.fetchSomeData()
.retry(5)  // Retry the call 5 times if it errors
.subscribeOn(Schedulers.io())  // execute the call asynchronously
.observeOn(AndroidSchedulers.mainThread())  // handle the results in the ui thread
.subscribe(onComplete, onError);
// onComplete and onError are of type Action1<DataResponse>, Action1<Throwable>
// Here you can define what to do with the results

I had the same problem like you and this was actually my solution. RxJava is a really nice library to use in combination with Retrofit. You can even do many cool things in addition to retrying (like e.g. composing and chaining calls).

It seems it will be present in retrofit 2.0 from the API Spec: https://github.com/square/retrofit/issues/297. Currently, the best way seems to be catch exception and retry manually.

For Retrofit 2.x;

You can use Call.clone() method to clone request and execute it.

For Retrofit 1.x;

You can use Interceptors. Create a custom interceptor

    OkHttpClient client = new OkHttpClient();
client.setConnectTimeout(CONNECT_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS);
client.setReadTimeout(READ_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS);
client.interceptors().add(new Interceptor() {
@Override
public Response intercept(Chain chain) throws IOException {
Request request = chain.request();


// try the request
Response response = chain.proceed(request);


int tryCount = 0;
while (!response.isSuccessful() && tryCount < 3) {


Log.d("intercept", "Request is not successful - " + tryCount);


tryCount++;


// retry the request
response.close()
response = chain.proceed(request);
}


// otherwise just pass the original response on
return response;
}
});

And use it while creating RestAdapter.

new RestAdapter.Builder()
.setEndpoint(API_URL)
.setRequestInterceptor(requestInterceptor)
.setClient(new OkClient(client))
.build()
.create(Adapter.class);

As stated in the docs, a better might be to use the baked in authenticators, eg: private final OkHttpClient client = new OkHttpClient();

  public void run() throws Exception {
client.setAuthenticator(new Authenticator() {
@Override public Request authenticate(Proxy proxy, Response response) {
System.out.println("Authenticating for response: " + response);
System.out.println("Challenges: " + response.challenges());
String credential = Credentials.basic("jesse", "password1");
return response.request().newBuilder()
.header("Authorization", credential)
.build();
}


@Override public Request authenticateProxy(Proxy proxy, Response response) {
return null; // Null indicates no attempt to authenticate.
}
});


Request request = new Request.Builder()
.url("http://publicobject.com/secrets/hellosecret.txt")
.build();


Response response = client.newCall(request).execute();
if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);


System.out.println(response.body().string());
}

The problem with response.isSuccessful() is when you have an exception like SocketTimeoutException.

I modified the original code to fix it.

OkHttpClient client = new OkHttpClient();
client.setConnectTimeout(CONNECT_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS);
client.setReadTimeout(READ_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS);
client.interceptors().add(new Interceptor() {
@Override
public Response intercept(Chain chain) throws IOException {
Request request = chain.request();
Response response = null;
boolean responseOK = false;
int tryCount = 0;


while (!responseOK && tryCount < 3) {
try {
response = chain.proceed(request);
responseOK = response.isSuccessful();
}catch (Exception e){
Log.d("intercept", "Request is not successful - " + tryCount);
}finally{
tryCount++;
}
}


// otherwise just pass the original response on
return response;
}
});

Hope it helps. Regards.

I found the way(OKHttpClient intercepter) provided by Sinan Kozak does not work when http connection failed, there is nothing yet concerned with HTTP response.

So i use another way to hook the Observable object, call .retryWhen on it. Also, i have added retryCount limit.

import retrofit2.Call;
import retrofit2.CallAdapter;
import retrofit2.Retrofit;
import retrofit2.adapter.rxjava.HttpException;
import retrofit2.adapter.rxjava.RxJavaCallAdapterFactory;
import retrofit2.converter.jackson.JacksonConverterFactory;
import rx.Observable;
import java.io.IOException;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;

Then

    RxJavaCallAdapterFactory originCallAdaptorFactory = RxJavaCallAdapterFactory.create();


CallAdapter.Factory newCallAdaptorFactory = new CallAdapter.Factory() {
@Override
public CallAdapter<?> get(Type returnType, Annotation[] annotations, Retrofit retrofit) {


CallAdapter<?> ca = originCallAdaptorFactory.get(returnType, annotations, retrofit);


return new CallAdapter<Observable<?>>() {


@Override
public Type responseType() {
return ca.responseType();
}


int restRetryCount = 3;


@Override
public <R> Observable<?> adapt(Call<R> call) {
Observable<?> rx = (Observable<?>) ca.adapt(call);


return rx.retryWhen(errors -> errors.flatMap(error -> {
boolean needRetry = false;
if (restRetryCount >= 1) {
if (error instanceof IOException) {
needRetry = true;
} else if (error instanceof HttpException) {
if (((HttpException) error).code() != 200) {
needRetry = true;
}
}
}


if (needRetry) {
restRetryCount--;
return Observable.just(null);
} else {
return Observable.error(error);
}
}));
}
};
}
};

Then add or replace

.addCallAdapterFactory(RxJavaCallAdapterFactory.create())

with

.addCallAdapterFactory(newCallAdaptorFactory)

For example:

return new Retrofit
.Builder()
.baseUrl(baseUrl)
.client(okClient)
.addCallAdapterFactory(newCallAdaptorFactory)
.addConverterFactory(JacksonConverterFactory.create(objectMapper));

Note: For simplicity, i just treat HTTP code > 404 code as retry, please modify it for yourself.

Besides, if http response is 200, then above rx.retryWhen will not get called, if you insist check such a response, you can add rx.subscribeOn(...throw error... before .retryWhen.

I have play a lot with this problem trying to find how is the best way to retry Retrofit requests. I am using Retrofit 2 so my solution is for Retrofit 2. For Retrofit 1 you have to use Interceptor like the accepted answer here. The answer of @joluet is correct but he did not mention that retry method need to be called before .subscribe(onComplete, onError) method. This is very important otherwise the request wouldn't be retried again like @pocmo mentioned in @joluet answer. Here is my example:

final Observable<List<NewsDatum>> newsDetailsObservable = apiService.getCandidateNewsItem(newsId).map((newsDetailsParseObject) -> {
return newsDetailsParseObject;
});


newsDetailsObservable.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.retry((integer, throwable) -> {
//MAX_NUMBER_TRY is your maximum try number
if(integer <= MAX_NUMBER_TRY){
return true;//this will retry the observable (request)
}
return false;//this will not retry and it will go inside onError method
})
.subscribe(new Subscriber<List<NewsDatum>>() {
@Override
public void onCompleted() {
// do nothing
}


@Override
public void onError(Throwable e) {
//do something with the error
}


@Override
public void onNext(List<NewsDatum> apiNewsDatum) {
//do something with the parsed data
}
});

apiService is my RetrofitServiceProvider object.

BTW : I am using Java 8 so a lot of lambda expressions are inside the code.

For those prefer an interceptor to deal with the issue of retrying - Building upon Sinan's answer, here is my proposed interceptor, which includes both retry count and back-off delay, and only retries attempts when network is available, and when request wasn't cancelled. (only deals with IOExceptions (SocketTimeout, UnknownHost, etc.))

    builder.addInterceptor(new Interceptor() {
@Override
public Response intercept(Chain chain) throws IOException {
Request request = chain.request();


// try the request
Response response = null;
int tryCount = 1;
while (tryCount <= MAX_TRY_COUNT) {
try {
response = chain.proceed(request);
break;
} catch (Exception e) {
if (!NetworkUtils.isNetworkAvailable()) {
// if no internet, dont bother retrying request
throw e;
}
if ("Canceled".equalsIgnoreCase(e.getMessage())) {
// Request canceled, do not retry
throw e;
}
if (tryCount >= MAX_TRY_COUNT) {
// max retry count reached, giving up
throw e;
}


try {
// sleep delay * try count (e.g. 1st retry after 3000ms, 2nd after 6000ms, etc.)
Thread.sleep(RETRY_BACKOFF_DELAY * tryCount);
} catch (InterruptedException e1) {
throw new RuntimeException(e1);
}
tryCount++;
}
}


// otherwise just pass the original response on
return response;
}
});

Courtesy to the top answer,This is what worked for me. If there is a connectivity issues, its better to wait for a few seconds before retry.

public class ErrorInterceptor implements Interceptor {
ICacheManager cacheManager;
Response response = null;
int tryCount = 0;
int maxLimit = 3;
int waitThreshold = 5000;
@Inject
public ErrorInterceptor() {


}


@Override
public Response intercept(Chain chain){


// String language =  cacheManager.readPreference(PreferenceKeys.LANGUAGE_CODE);
Request request = chain.request();
response =  sendReqeust(chain,request);
while (response ==null && tryCount < maxLimit) {
Log.d("intercept", "Request failed - " + tryCount);
tryCount++;
try {
Thread.sleep(waitThreshold); // force wait the network thread for 5 seconds
} catch (InterruptedException e) {
e.printStackTrace();
}
response = sendReqeust(chain,request);
}
return response;
}


private Response sendReqeust(Chain chain, Request request){
try {
response = chain.proceed(request);
if(!response.isSuccessful())
return null;
else
return response;
} catch (IOException e) {
return null;
}
}

}

Just want to share my version. It uses rxJava retryWhen method. My version retries connection every N=15 sec and almost immediately emit retry when internet connection recover.

public class RetryWithDelayOrInternet implements Function<Flowable<? extends Throwable>, Flowable<?>> {
public static boolean isInternetUp;
private int retryCount;


@Override
public Flowable<?> apply(final Flowable<? extends Throwable> attempts) {
return Flowable.fromPublisher(s -> {
while (true) {
retryCount++;
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
attempts.subscribe(s);
break;
}
if (isInternetUp || retryCount == 15) {
retryCount = 0;
s.onNext(new Object());
}
}
})
.subscribeOn(Schedulers.single());
}}

And you should use it before .subscribe like this:

.retryWhen(new RetryWithDelayOrInternet())

You should manually change isInternetUp field

public class InternetConnectionReceiver extends BroadcastReceiver {




@Override
public void onReceive(Context context, Intent intent) {
boolean networkAvailable = isNetworkAvailable(context);
RetryWithDelayOrInternet.isInternetUp = networkAvailable;
}
public static boolean isNetworkAvailable(Context context) {
ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();
return activeNetworkInfo != null && activeNetworkInfo.isConnected();
}}

I am of the opinion that you shouldn't mix API handling (done by retrofit/okhttp) with retries. Retrying mechanisms are more orthogonal, and can be used in many other contexts as well. So I use Retrofit/OkHTTP for all the API calls and request/response handling, and introduce another layer above, for retrying the API call.

In my limited Java experience so far, I have found jhlaterman's Failsafe library (github: jhalterman/failsafe) to be a very versatile library for handling many 'retry' situations cleanly. As an example, here's how I would use it with a retrofit instantiated mySimpleService, for authentication -

AuthenticationResponse authResp = Failsafe.with(
new RetryPolicy().retryOn(Arrays.asList(IOException.class, AssertionError.class))
.withBackoff(30, 500, TimeUnit.MILLISECONDS)
.withMaxRetries(3))
.onRetry((error) -> logger.warn("Retrying after error: " + error.getMessage()))
.get(() -> {
AuthenticationResponse r = mySimpleAPIService.authenticate(
new AuthenticationRequest(username,password))
.execute()
.body();


assert r != null;


return r;
});

The code above catches socket exceptions, connection errors, assertion failures, and retries on them maximum of 3 times, with exponential backoff. It also allows you to customise on-retry behaviour, and allows you to specify a fallback as well. It's quite configurable, and can adapt to most of the retry situations.

Feel free to check the documentation of the library as it offers many other goodies apart from just retries.

A solution that worked for me on OkHttp 3.9.1 (considering other answers for this question):

@NonNull
@Override
public Response intercept(@NonNull Chain chain) throws IOException {
Request  request      = chain.request();
int      retriesCount = 0;
Response response     = null;


do {
try {
response = chain.proceed(request);


// Retry if no internet connection.
} catch (ConnectException e) {
Log.e(TAG, "intercept: ", e);
retriesCount++;


try {
Thread.sleep(RETRY_TIME);


} catch (InterruptedException e1) {
Log.e(TAG, "intercept: ", e1);
}
}


} while (response == null && retriesCount < MAX_RETRIES);


// If there was no internet connection, then response will be null.
// Need to initialize response anyway to avoid NullPointerException.
if (response == null) {
response = chain.proceed(newRequest);
}


return response;
}

Working prod solution.

public int callAPI() {
return 1; //some method to be retried
}


public int retrylogic()  throws InterruptedException, IOException{
int retry = 0;
int status = -1;
boolean delay = false;
do {
if (delay) {
Thread.sleep(2000);
}


try {
status = callAPI();
}
catch (Exception e) {
System.out.println("Error occured");
status = -1;
}
finally {
switch (status) {
case 200:
System.out.println(" **OK**");
return status;
default:
System.out.println(" **unknown response code**.");
break;
}
retry++;
System.out.println("Failed retry " + retry + "/" + 3);
delay = true;


}
}while (retry < 3);


System.out.println("Aborting download of dataset.");
return status;
}

As a previous user said, if your are using Retrofit2 call.clone would suffice, but I also wanted to add a quick example on how that would look:

public class CallbackImpl implements Callback<ResponseBody> {
private final Set<Integer> retryCode = new HashSet<>(Arrays.asList(503, 504));
int requestRetry  = 1;


@Override
public void onResponse(Call<ResponseBody> call, Response<ResponseBody> response) {
if (response.code() == 201) {
// Object was created.
} else {
if (requestRetry != 0 && retryCode.contains(response.code())) {
call.clone().enqueue(this);
} else {
// Handle the error
}
}
}


@Override
public void onFailure(Call<ResponseBody> call, Throwable throwable) {
if (throwable instanceof IOException) {
// Network failure
} else {
// Conversion Issue
}
}
}

Resilience4j offers a highly configurable way of defining your retry behaviour and has retrofit adapters as an add-on module.

Example of the available options:

private final Retry retry = Retry.of("id", RetryConfig.<Response<String>>custom()
.maxAttempts(2)
.waitDuration(Duration.ofMillis(1000))
.retryOnResult(response -> response.code() == 500)
.retryOnException(e -> e instanceof WebServiceException)
.retryExceptions(IOException.class, TimeoutException.class)
.ignoreExceptions(BusinessException.class, OtherBusinessException.class)
.failAfterMaxAttempts(true)
.build());

See the resilience4j documentation on how to integrate that with Retrofit.