问题
How can I add retry functionality to the requests sent by Retrofit 2 library. Something like:
service.listItems().enqueue(new Callback<List<Item>>() {
@Override
public void onResponse(Response<List<Item>> response) {
...
}
@Override
public void onFailure(Throwable t) {
...
}
}).retryOnFailure(5 /* times */);
回答1:
I finally did something like this, for anyone interested:
1
First I made an abstract class CallbackWithRetry
public abstract class CallbackWithRetry<T> implements Callback<T> {
private static final int TOTAL_RETRIES = 3;
private static final String TAG = CallbackWithRetry.class.getSimpleName();
private final Call<T> call;
private int retryCount = 0;
public CallbackWithRetry(Call<T> call) {
this.call = call;
}
@Override
public void onFailure(Throwable t) {
Log.e(TAG, t.getLocalizedMessage());
if (retryCount++ < TOTAL_RETRIES) {
Log.v(TAG, "Retrying... (" + retryCount + " out of " + TOTAL_RETRIES + ")");
retry();
}
}
private void retry() {
call.clone().enqueue(this);
}
}
Using this class I can do something like this:
serviceCall.enqueue(new CallbackWithRetry<List<Album>>(serviceCall) {
@Override
public void onResponse(Response<List<Album>> response) {
...
}
});
2
This is not completely satisfactory because I have to pass same serviceCall twice. This can confusing as one can think the second serviceCall (that goes into constructor of CallbackWithRetry) should or could be something different from first one (which we invoke enqueue method on it)
So I implemented a helper class CallUtils:
public class CallUtils {
public static <T> void enqueueWithRetry(Call<T> call, final Callback<T> callback) {
call.enqueue(new CallbackWithRetry<T>(call) {
@Override
public void onResponse(Response<T> response) {
callback.onResponse(response);
}
@Override
public void onFailure(Throwable t) {
super.onFailure(t);
callback.onFailure(t);
}
});
}
}
And I can use it like this:
CallUtils.enqueueWithRetry(serviceCall, new Callback<List<Album>>() {
@Override
public void onResponse(Response<List<Album>> response) {
...
}
@Override
public void onFailure(Throwable t) {
// Let the underlying method do the job of retrying.
}
});
With this I have to pass a standard Callback to enqueueWithRetry method and it makes me implement onFailure (Though in the previous method I can implement it too)
So this is how I've solved the issue. Any suggestion for a better design would be appreciated.
回答2:
I've made custom implementation of the Callback interface, you can pretty much use it in place of original callback. If call is successful, the onResponse() method is called. If after retrying for set amount of repetitions call fails, onFailedAfterRetry() is called.
public abstract class BackoffCallback<T> implements Callback<T> {
private static final int RETRY_COUNT = 3;
/**
* Base retry delay for exponential backoff, in Milliseconds
*/
private static final double RETRY_DELAY = 300;
private int retryCount = 0;
@Override
public void onFailure(final Call<T> call, Throwable t) {
retryCount++;
if (retryCount <= RETRY_COUNT) {
int expDelay = (int) (RETRY_DELAY * Math.pow(2, Math.max(0, retryCount - 1)));
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
retry(call);
}
}, expDelay);
} else {
onFailedAfterRetry(t);
}
}
private void retry(Call<T> call) {
call.clone().enqueue(this);
}
public abstract void onFailedAfterRetry(Throwable t);
}
https://gist.github.com/milechainsaw/811c1b583706da60417ed10d35d2808f
回答3:
Go with RxJava Observable and call retry() Doc: https://github.com/ReactiveX/RxJava/wiki/Error-Handling-Operators
回答4:
I did something quite similar to Ashkan Sarlak, but since Retrofit 2.1 passes the Call<T> into the onFailure method, you can simplify to one CallbackWithRetry<T> abstract class. See:
public abstract class CallbackWithRetry<T> implements Callback<T> {
private static final String TAG = "CallbackWithRetry";
private int retryCount = 0;
private final Logger logger;
private final String requestName;
private final int retryAttempts;
protected CallbackWithRetry(@NonNull Logger logger, @NonNull String requestName, int retryAttempts) {
this.logger = logger;
this.requestName = requestName;
this.retryAttempts = retryAttempts;
}
@Override
public void onFailure(Call<T> call, Throwable t) {
if (retryCount < retryAttempts) {
logger.e(TAG, "Retrying ", requestName, "... (", retryCount, " out of ", retryAttempts, ")");
retry(call);
retryCount += 1;
} else {
logger.e(TAG, "Failed request ", requestName, " after ", retryAttempts, " attempts");
}
}
private void retry(Call<T> call) {
call.clone().enqueue(this);
}
}
回答5:
ashkan-sarlak answer work great and i'm just try to make it up to date.
From retrofit 2.1
onFailure(Throwable t)
Change to
onFailure(Call<T> call, Throwable t)
So this make it so easy now.just create CallbackWithRetry.java like this
public abstract class CallbackWithRetry<T> implements Callback<T> {
private static final int TOTAL_RETRIES = 3;
private static final String TAG = CallbackWithRetry.class.getSimpleName();
private int retryCount = 0;
@Override
public void onFailure(Call<T> call, Throwable t) {
Log.e(TAG, t.getLocalizedMessage());
if (retryCount++ < TOTAL_RETRIES) {
Log.v(TAG, "Retrying... (" + retryCount + " out of " + TOTAL_RETRIES + ")");
retry(call);
}
}
private void retry(Call<T> call) {
call.clone().enqueue(this);
}
}
That's all! you can simply use it like this
call.enqueue(new CallbackWithRetry<someResponseClass>() {
@Override
public void onResponse(@NonNull Call<someResponseClass> call, @NonNull retrofit2.Response<someResponseClass> response) {
//do what you want
}
@Override
public void onFailure(@NonNull Call<someResponseClass> call, @NonNull Throwable t) {
super.onFailure(call,t);
//do some thing to show ui you trying
//or don't show! its optional
}
});
回答6:
I think for android we no need to go for retrofit for this.We can make use of Workmanager (which predefine android api). We can use "ListenableWorker.Result.SUCCESS","ListenableWorker.Result.RETRY" ,etc and achieve the above goals.
回答7:
With Retrofit 2.5
Now it's possible to make async sync calls through java.util.concurrent.CompletableFuture, the code waits for it's completion wich is very nice.
Here's a gist with a working solution.
来源：https://stackoverflow.com/questions/32579754/retrying-the-request-using-retrofit-2