Failsafe RetryPolicy - throw exception from supplyAsync

Question

I'm implementing a retry policy. Basically what I want to do is retry a POST request on a separate thread. I'm using Failsafe (https://failsafe.dev/async-execution/#async-integration) Here is my code

Failsafe.with(retryPolicy).with(executor).future(() -> CompletableFuture.supplyAsync(() -> {
            try {
                CloseableHttpResponse response = client.execute(httpPost);
                httpPost.releaseConnection();
                client.close();
                return response;
            } catch (IOException e) {
                return null;
            }
        }).thenApplyAsync(response -> "Response: " + response)
          .thenAccept(System.out::println));

I don't want to catch the IOException here. It is handled by the retry policy. Currently retrying won't happen since I'm catching the exception here. Is there a way to throw an exception from 'supplyAsync' so it will be handled by the retry policy? Thanks. Thanks

Answer 1

CompletionStage API gives several different ways of handling and dealing with unchecked exceptions. But in your case what you get is a Checked exception and you are out of luck. You either have to handle it or throw it outward towards your caller. Here's a one way of doing it, if you prefer the latter approach.

Failsafe.with(retryPolicy).with(executor).future(() -> CompletableFuture.supplyAsync(() -> {
            try {
                // Remainder omitted
                return response;
            } catch (IOException e) {
                throw new CompletionException(e);
            }
        }).thenApplyAsync(response -> "Response: " + response)
          .thenAccept(System.out::println));