👀 Views: 99 💬 Answers: 1 📅 Created: 2025-06-07

spring-boot threadlocal memory-leaks filters Java

I'm relatively new to this, so bear with me. I'm working with a question where values set in a `ThreadLocal` variable are not being cleared after the request is processed in my Spring Boot 2.6 application. This leads to memory leaks and stale data being served on subsequent requests. I have a `ThreadLocal` variable that stores user session information, and I'm using it to manage user state effectively across different layers of my application. However, I noticed that if a request fails or if an exception is thrown, the `ThreadLocal` variable still retains its value. Here's the relevant part of my code: ```java public class UserContext { private static final ThreadLocal<String> userId = new ThreadLocal<>(); public static void setUserId(String id) { userId.set(id); } public static String getUserId() { return userId.get(); } public static void clear() { userId.remove(); } } ``` And in my controller, I have a filter that sets the user ID: ```java @Component public class UserContextFilter implements Filter { @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { try { String userIdFromRequest = // logic to extract user ID from request; UserContext.setUserId(userIdFromRequest); chain.doFilter(request, response); } finally { UserContext.clear(); } } } ``` While the `clear()` method is being called in the `finally` block, I still see that under high load, the variable sometimes retains previously set values, especially when multiple requests are processed concurrently. I've added logging to check when `clear()` is called, and it appears to be invoked every time. I also checked that there are no other parts of my code that could be inadvertently calling the `setUserId()` method without a corresponding `clear()`. Is there a specific best practice for managing `ThreadLocal` in a Spring Boot application, or could there be something related to the application's threading model that I'm missing? Any insights would be greatly appreciated!