How to prevent memory leaks in a Java Servlet when using an external API?
I'm wondering if anyone has experience with I'm working on a project and hit a roadblock... I'm currently working on a Java Servlet that interacts with an external REST API to fetch user data. The servlet is designed to handle multiple requests, and it uses a thread pool for managing concurrent requests. However, I've noticed that the application seems to be consuming more memory over time, which leads me to suspect that there might be a memory leak. After profiling the application with VisualVM, I found that instances of a certain class, `UserService`, are not being garbage collected. Here's a snippet of my servlet code: ```java public class UserServlet extends HttpServlet { private ExecutorService executorService = Executors.newFixedThreadPool(10); @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String userId = request.getParameter("userId"); executorService.submit(() -> { try { UserService userService = new UserService(); // suspected leak User user = userService.fetchUserData(userId); response.getWriter().println(user.toString()); } catch (Exception e) { e.printStackTrace(); } }); } } ``` The `UserService` class holds a reference to a large cache of data fetched from the external API, but I'm unsure how to properly manage its lifecycle. I've tried moving the `UserService` instantiation outside the method, thinking it might reduce memory usage, but that led to stale data being used across multiple requests. I also considered using a singleton pattern, but I'm worried about state management and thread safety. Additionally, I have checked for any unclosed resources, like streams or connections, and confirmed they are properly closed after usage. However, the memory usage continues to increase, and I'm receiving a `java.lang.OutOfMemoryError: Java heap space` after a few hours of performance testing. Is there a recommended approach for managing object lifecycles in this context? How can I ensure that I'm not inadvertently holding onto objects longer than necessary? Any insights or best practices would be greatly appreciated. For context: I'm using Java on Linux. What am I doing wrong? I'm working on a API that needs to handle this. What am I doing wrong? This is my first time working with Java stable. Am I missing something obvious?