👀 Views: 32 💬 Answers: 1 📅 Created: 2025-06-05

java completablefuture exception-handling executorservice Java

I'm building a feature where I'm currently working with Java 11 and running into an issue with `CompletableFuture` when trying to handle exceptions that arise during asynchronous processing... I've set up an `ExecutorService` to manage my tasks, and I'm using `CompletableFuture.supplyAsync()` to execute a task. However, when an exception occurs in the task, it seems like the exception isn't being caught as I expect. Here’s a simplified version of my code: ```java import java.util.concurrent.*; public class CompletableFutureExample { public static void main(String[] args) { ExecutorService executor = Executors.newFixedThreadPool(2); CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> { if (true) throw new RuntimeException("Simulated exception"); return "Task completed"; }, executor); future.exceptionally(ex -> { System.out.println("Caught exception: " + ex.getMessage()); return "Default Value"; }); future.thenAccept(result -> System.out.println("Result: " + result)); executor.shutdown(); } } ``` When I run this code, I see the message "Caught exception: Simulated exception" being printed, but then I also see that the `thenAccept` stage is being called with a `null` value. I expected the `exceptionally` block to handle the exception and provide a default value that should then be passed to the `thenAccept` stage. Instead, it seems like the execution is just moving forward with `null`. I've tried moving the `thenAccept` to be within the `exceptionally` block, but that didn’t resolve the issue either. Shouldn't the `result` in `thenAccept` be the default value I returned in the `exceptionally` block? What am I missing here in the flow of `CompletableFuture`? Any insights would be greatly appreciated! Is this even possible?