Java 11 CompletableFuture Not Handling Exceptions as Expected in Async Processing
I've tried everything I can think of but I'm experimenting with I'm optimizing some code but I'm stuck on something that should probably be simple... I'm working with Java 11 and using `CompletableFuture` to handle asynchronous processing in my application. I have a use case where I fetch data from a remote API and process it. However, I'm running into an scenario where exceptions thrown during the processing phase are not being caught as expected. Here's a simplified version of my code: ```java import java.util.concurrent.CompletableFuture; import java.util.concurrent.ExecutionException; public class AsyncExample { public static void main(String[] args) { CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> { // Simulate API call if (Math.random() > 0.5) { throw new RuntimeException("API call failed"); } return "Data from API"; }).thenApply(data -> { // Process data if (data.equals("Data from API")) { throw new IllegalArgumentException("Processing behavior"); } return data.toUpperCase(); }); try { String result = future.get(); // This hangs if there's an exception System.out.println(result); } catch (ExecutionException e) { System.err.println("Caught exception: " + e.getCause().getMessage()); } catch (InterruptedException e) { Thread.currentThread().interrupt(); } } } ``` When I run this, if the `supplyAsync` method throws an exception, it seems to propagate correctly to the `ExecutionException`. However, when the `thenApply` stage throws an exception, the `future.get()` hangs indefinitely, and I never reach the catch block. I expected to see the exception caught and handled. I've tried adding a `handle` method to manage exceptions, but that doesn't seem to resolve the hanging scenario. ```java CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> { // Same logic as before }).handle((result, throwable) -> { if (throwable != null) { System.err.println("Handled exception: " + throwable.getMessage()); return null; } return result; }); ``` Despite this, the future still doesn't complete as expected when an exception occurs in `thenApply`. Am I missing something in my usage of `CompletableFuture`, or is there a specific handling I should be doing for exceptions in chained stages? Any help would be greatly appreciated! I'm working on a CLI tool that needs to handle this. What am I doing wrong? For reference, this is a production mobile app. Hoping someone can shed some light on this. I'm on Ubuntu 20.04 using the latest version of Java. The stack includes Java and several other technologies. Is there a better approach?