👀 Views: 83 💬 Answers: 1 📅 Created: 2025-07-22

java stream optional Java

I need help solving I'm facing a problem when using the Stream API combined with Optional in Java 17 while processing a nested data structure. I have a list of `User` objects, and each `User` has an `Optional<List<Order>>` field. The goal is to filter users who have at least one order and then collect their usernames into a list. However, I’m getting a `NoSuchElementException` when trying to access the orders. Here's a simplified version of my code: ```java import java.util.*; import java.util.stream.Collectors; class User { private String username; private Optional<List<Order>> orders; public User(String username, Optional<List<Order>> orders) { this.username = username; this.orders = orders; } public String getUsername() { return username; } public Optional<List<Order>> getOrders() { return orders; } } class Order { private String orderId; public Order(String orderId) { this.orderId = orderId; } } public class Main { public static void main(String[] args) { List<User> users = Arrays.asList( new User("Alice", Optional.of(Arrays.asList(new Order("1")))), new User("Bob", Optional.empty()), new User("Charlie", Optional.of(Arrays.asList(new Order("2")))) ); List<String> usernamesWithOrders = users.stream() .filter(user -> user.getOrders().isPresent() && !user.getOrders().get().isEmpty()) .map(User::getUsername) .collect(Collectors.toList()); System.out.println(usernamesWithOrders); } } ``` When I run this code, it works fine, but I've noticed that if I have a user with an empty `Optional` list instead of an empty `List`, I sometimes get an exception on the line where I call `.get()` on `user.getOrders()`. I suspect it's related to the order in which the checks happen in the filter. I've tried using `flatMap` instead of `isPresent()` and `get()`, but that resulted in an empty list being returned even when there are valid users. What is the best approach to handle this situation without running into exceptions? Any suggestions or best practices for working with nested Optionals in this context? What's the best practice here? I recently upgraded to Java 3.10. Has anyone else encountered this?