Gather a username and password, validates the user, then allows the user to access other pages.
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 FormLogin 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;
}
}
Related examples in the same category
