advanced patterns with CompletableFuture Combining Multiple Async Tasks in Java 17
I'm performance testing and I've searched everywhere and can't find a clear answer. I'm working with an scenario when trying to combine multiple asynchronous tasks using `CompletableFuture` in Java 17. I have a scenario where I want to fetch data from two different APIs concurrently and then merge their results. However, I'm seeing that sometimes the combined result is not what I expect, particularly when one of the API calls fails. Here's a simplified version of my code: ```java CompletableFuture<JsonNode> api1Future = CompletableFuture.supplyAsync(() -> fetchFromApi1()); CompletableFuture<JsonNode> api2Future = CompletableFuture.supplyAsync(() -> fetchFromApi2()); CompletableFuture<JsonNode> combinedFuture = api1Future.thenCombine(api2Future, (result1, result2) -> { // Merging logic return mergeResults(result1, result2); }); try { JsonNode combinedResult = combinedFuture.get(); // Blocking call System.out.println("Combined Result: " + combinedResult); } catch (ExecutionException e) { System.err.println("behavior during execution: " + e.getCause().getMessage()); } catch (InterruptedException e) { Thread.currentThread().interrupt(); } ``` The scenario arises when `fetchFromApi2()` fails due to a timeout. In that case, it seems like `combinedFuture` completes exceptionally, but I can’t figure out how to handle this gracefully. Instead of logging the behavior and returning a fallback value, it throws an `ExecutionException` when I call `get()`. I've tried wrapping the `thenCombine` logic in a `handle()` method, but I still see the same exception. Here's what I attempted: ```java CompletableFuture<JsonNode> combinedFuture = api1Future.handle((result1, throwable) -> { if (throwable != null) { return fallbackValue; } return result1; }).thenCombine(api2Future, (result1, result2) -> { return mergeResults(result1, result2); }); ``` The `handle()` method only deals with the first future's result and not the second. I would appreciate any suggestions on how to effectively manage this situation to prevent an unhandled exception and possibly return a combined result even if one of the API calls fails. Moreover, is there a best practice for merging results from multiple asynchronous operations in Java when potential failures are involved? I'm working on a application that needs to handle this. Is there a better approach? Cheers for any assistance!