Summary
Implementing remember-me functionality can be challenging, as seen in the given example. The author tried various approaches, including solutions proposed by BalusC and Ilyua Basin, but faced issues such as session inconsistencies and cookie management problems.
Root Cause
The root cause of the problems lies in the incorrect handling of sessions and cookies in the filter and servlet. Specifically, the filter is called multiple times during the login process, and the session is not properly managed, leading to null sessions and incorrect cookie management.
Why This Happens in Real Systems
This issue occurs in real systems due to the complexities of handling sessions and cookies in a servlet-based system. The filter and servlet need to work together seamlessly to manage the session and cookies, which can be challenging, especially when dealing with multiple requests and redirects.
Real-World Impact
The impact of this issue is significant, as it affects the user experience and security of the application. Users may be unable to log in or stay logged in, and the application may be vulnerable to security breaches due to incorrect cookie management.
Example or Code
public class MyServletFilter extends SecurityParentServlet implements Filter {
//...
@Override
public void doFilter(ServletRequest req, ServletResponse resp, FilterChain fchain) throws IOException, ServletException {
//...
// Check if the user is logged in and has a valid session
HttpSession session = request.getSession(false);
if ((session!= null) && (session.getAttribute("user")!= null)) {
fchain.doFilter(req, resp);
return;
}
//...
}
}How Senior Engineers Fix It
Senior engineers fix this issue by properly managing sessions and cookies in the filter and servlet. They ensure that the session is correctly created and managed throughout the login process and that cookies are properly set and deleted. They also handle multiple requests and redirects correctly, ensuring that the filter and servlet work together seamlessly.
Why Juniors Miss It
Junior engineers may miss this issue due to a lack of experience with servlet-based systems and session and cookie management. They may not fully understand the complexities of handling multiple requests and redirects, leading to incorrect session and cookie management. Additionally, they may not thoroughly test their code, missing potential issues and edge cases.