Java 8: Struggling to Handle Custom Exceptions within CompletableFuture Chain
I've been struggling with this for a few days now and could really use some help. I'm working with an scenario when using `CompletableFuture` in Java 8 and trying to manage custom exceptions that occur during an asynchronous computation. I have a method that fetches user data from an API and processes it, but if the API call fails, I want to throw a custom exception. Instead of catching the exception and handling it gracefully, the entire future appears to be completed exceptionally with an `ExecutionException`, which is not what I expected. When I try to handle the exception in the `handle` method, it keeps returning the original exception instead of letting me define a fallback behavior. Here's a simplified version of my code: ```java import java.util.concurrent.CompletableFuture; public class UserService { public CompletableFuture<User> fetchUser(int userId) { return CompletableFuture.supplyAsync(() -> { // Simulating API call if (userId < 1) { throw new UserNotFoundException("User not found: " + userId); } return new User(userId, "John Doe"); }); } public CompletableFuture<User> getUserWithFallback(int userId) { return fetchUser(userId) .handle((user, throwable) -> { if (throwable != null) { // Here, I want to return a default user or log the behavior System.out.println(throwable.getMessage()); return new User(0, "Default User"); } return user; }); } } ``` When I invoke `getUserWithFallback(-1)`, I receive an `ExecutionException` instead of my custom fallback user. Here’s the stack trace I see: ``` java.util.concurrent.CompletionException: User not found: -1 at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:273) at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:280) ... ``` Is there a better way to handle this situation? I want to ensure that my custom exception is caught and handled correctly within the `CompletableFuture` chain without propagating the original exception. Any insights or best practices would be greatly appreciated! What's the best practice here?