Untitled

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class LoginServlet extends HttpServlet {
  public static String USER_KEY = "ServletLogin.user";

  public static String FIELD_USER = "username";

  public static String FIELD_PASSWORD = "password";

  public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException,
      java.io.IOException {
    resp.setContentType("text/html");
    java.io.PrintWriter out = resp.getWriter();
    resp.setHeader("Expires", "Tues, 01 Jan 1980 00:00:00 GMT");
    String uri = req.getRequestURI();

    HttpSession session = req.getSession();
    String user = (String) session.getAttribute(USER_KEY);

    if (user == null) {
      login(out, uri);
      return;
    }
    out.println("<html>");
    out.println("<head>");
    out.println("<title>Welcome</title>");
    out.println("</head>");
    out.println("<body>");
    out.println("<center><h2>Welcome to our site!</h2>");
    out.println("</center><br><br>");
    out.println("</body>");
    out.println("</html>");
    out.flush();
  }

  public void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException,
      java.io.IOException {
    resp.setContentType("text/html");
    java.io.PrintWriter out = resp.getWriter();
    HttpSession session = req.getSession(true);
    String user = (String) session.getAttribute(USER_KEY);

    if (user == null) {
      String username = req.getParameter(FIELD_USER);
      String password = req.getParameter(FIELD_PASSWORD);

      if (!validUser(username, password)) {
        out.println("<html>");
        out.println("<title>Invalid User</title>");
        out.println("<body><center><h2>" + "Invalid User!</h2><br>");
        out.println("Press the 'Back' button to try again");
        out.println("</center></body></html>");
        out.flush();
        return;
      }
      session.setAttribute(USER_KEY, username);
    }
    resp.sendRedirect(req.getRequestURI());
  }

  protected void login(java.io.PrintWriter out, String uri) throws java.io.IOException {
    out.println("<html>");
    out.println("<head>");
    out.println("<title>Login</title>");
    out.println("<center><h2>Welcome! Please login</h2>");
    out.println("<br><form method=POST action=\"" + uri + "\">");
    out.println("<table>");
    out.println("<tr><td>User ID:</td>");
    out.println("<td><input type=text name=" + FIELD_USER + " size=30></td></tr>");
    out.println("<tr><td>Password:</td>");
    out.println("<td><input type=password name=" + FIELD_PASSWORD + " size=10></td></tr>");
    out.println("</table><br>");
    out.println("<input type=submit value=\"Login\">");
    out.println("</form></center></body></html>");
  }

  protected boolean validUser(String username, String password) {
    boolean valid = false;
    if ((username != null) && (username.length() > 0)) {
      valid = username.equals(password);
    }

    return valid;
  }
}