Issues with Java Stream API and Performance When Filtering Large Collections
Hey everyone, I'm running into an issue that's driving me crazy. Does anyone know how to I've been banging my head against this for hours. I'm encountering a significant performance issue when using the Java Stream API to filter large collections. My application processes a list of `User` objects to find those who are active and have a specific role. The collection can contain over a million records, and I noticed that the filtering operation takes an unexpectedly long time, especially when running it in a multi-threaded environment. Here's a simplified version of the code I'm using: ```java import java.util.List; import java.util.stream.Collectors; public class User { private String name; private boolean isActive; private String role; // Constructor, getters, and setters } public class UserService { private List<User> users; public List<User> getActiveUsersWithRole(String role) { return users.stream() .filter(User::isActive) .filter(user -> user.getRole().equals(role)) .collect(Collectors.toList()); } } ``` I've tried profiling the application using VisualVM, and it shows that the filtering step accounts for the majority of the processing time, particularly when there's a high number of inactive users. Loading the `users` list from a database and performing the filtering in-memory seems to be the bottleneck, particularly if the list contains many irrelevant entries. Also, I attempted to parallelize the stream using `parallelStream()`, but it didn’t yield a noticeable improvement. In fact, I sometimes noticed worse performance with `parallelStream()` due to thread contention. Is there a more efficient way to handle this filtering process, especially given that I need to scale the application to handle even larger datasets? Any best practices or alternative approaches would be appreciated. Am I missing something obvious? This is part of a larger service I'm building. This is happening in both development and production on Linux.