Why does Authorization Redirect on Session Expiration Behave Differently for Page Navigation and Form Submit in JSF?

Authorization Redirect on Session Expiration: Different Outcomes Between Page Navigation and Form Submit

Customizing the FacesServlet to implement authorization and session management is a common practice in JSF applications. However, a peculiar issue arises where redirecting on session expiration behaves differently for page navigation and form submissions.

Problem Description

When using a custom FacesServlet to check authorization and redirect unauthorized users, the redirect response fails to take effect when a JSF form is submitted. The page remains unchanged despite the redirect command in the servlet.

Understanding the Difference

The divergence between behavior for page navigation and form submit resides in the type of request they send. Page navigation involves a regular HTTP request, while JSF form submissions trigger an AJAX request.

Ajax and XML Response

AJAX requests expect an XML response. If a redirect is sent as an AJAX response, the AJAX engine re-sends the request to the redirect URL. Since the redirect URL returns an HTML page instead of the required XML, the browser fails to handle the response properly.

Filter as a Better Solution

Rather than using a modified FacesServlet, a servlet filter is a more suitable approach for this authorization scenario. Filters can intercept requests before they reach servlets, making them an ideal choice for security and session handling.

Example Filter Implementation

Below is an example of a servlet filter that implements authorization and session expiration handling:

<code class="java">@WebFilter("/*")
public class AuthorizationFilter implements Filter {

    // ...

    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws ServletException, IOException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;
        HttpSession session = request.getSession(false);
        String loginURL = request.getContextPath() + "/login.xhtml";

        boolean loggedIn = (session != null) && (session.getAttribute("user") != null);
        boolean loginRequest = request.getRequestURI().equals(loginURL);
        boolean resourceRequest = request.getRequestURI().startsWith(request.getContextPath() + ResourceHandler.RESOURCE_IDENTIFIER + "/");
        boolean ajaxRequest = "partial/ajax".equals(request.getHeader("Faces-Request"));

        if (loggedIn || loginRequest || resourceRequest) {
            // Continue request without intervention
            chain.doFilter(request, response);
        } else if (ajaxRequest) {
            // Send an AJAX-style redirect response
            response.setContentType("text/xml");
            response.setCharacterEncoding("UTF-8");
            response.getWriter().printf(AJAX_REDIRECT_XML, loginURL);
        } else {
            // Perform standard synchronous redirect
            response.sendRedirect(loginURL);
        }
    }
}</code>

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