Authentication filter and servlet for login

Question

I\'ve a filter used for the login. It performs a textual checking, on fields \"Username\" and \"Password\". If and only if the textual checking is correctly done the request

Answer 1

Preface: I gather you're using homegrown login instead of container managed login. For all ways, see How to handle authentication/authorization with users in a database?

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The filter (the interceptor) shouldn't check the validity of the username/password combo. That's the responsibility of the servlet (the controller).

The filter should merely check if the user is logged-in or not (usually by just checking the presence of a session attribute) and then continue the request or block it by redirecting back to the login page.

@WebFilter("/*")
public class LoginFilter 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 loginURI = request.getContextPath() + "/login";

        boolean loggedIn = session != null && session.getAttribute("user") != null;
        boolean loginRequest = request.getRequestURI().equals(loginURI);

        if (loggedIn || loginRequest) {
            chain.doFilter(request, response);
        } else {
            response.sendRedirect(loginURI);
        }
    }

    // ...
}

The servlet should collect the submitted data, find the associated User in database and if found then store it as a session attribute and then redirect to the home page, else redisplay the form with validation errors.

@WebServlet("/login")
public class LoginServlet extends HttpServlet {

    @EJB
    private UserService userService;

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.getRequestDispatcher("/WEB-INF/login.jsp").forward(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        Map<String, String> messages = new HashMap<String, String>();

        if (username == null || username.isEmpty()) {
            messages.put("username", "Please enter username");
        }

        if (password == null || password.isEmpty()) {
            messages.put("password", "Please enter password");
        }

        if (messages.isEmpty()) {
            User user = userService.find(username, password);

            if (user != null) {
                request.getSession().setAttribute("user", user);
                response.sendRedirect(request.getContextPath() + "/home");
                return;
            } else {
                messages.put("login", "Unknown login, please try again");
            }  
        }

        request.setAttribute("messages", messages);
        request.getRequestDispatcher("/WEB-INF/login.jsp").forward(request, response);
    }

}

See also:

• Our servlet-filters wiki page
• Our servlets wiki page