Snippet

ThreadLocal Memory Leak Prevention in Custom Spring Interceptors

When using ThreadLocal variables in a thread-pooled environment like Spring MVC on Tomcat, failing to invoke remove() in afterCompletion causes memory leaks and stale tenant context retention across reused worker threads.

snippet.java

java

@Component
public class TenantContextInterceptor implements HandlerInterceptor {
    private static final ThreadLocal<String> TENANT_HOLDER = new ThreadLocal<>();
 
    public static String getCurrentTenant() {
        return TENANT_HOLDER.get();
    }
 
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
        String tenantId = request.getHeader("X-Tenant-ID");
        if (tenantId != null) {
            TENANT_HOLDER.set(tenantId);
        }
        return true;
    }
 
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
        TENANT_HOLDER.remove();
    }
}

spring

Breakdown

private static final ThreadLocal<String> TENANT_HOLDER = new ThreadLocal<>();

Maintains thread-confined state across service boundaries for the active HTTP request.

TENANT_HOLDER.set(tenantId);

Allocates tenant identity in the current thread's ThreadLocalMap.

TENANT_HOLDER.remove();

Explicitly removes the entry in afterCompletion to prevent memory leaks during thread reuse.

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ThreadLocal Memory Leak Prevention in Custom Spring Interceptors

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