/** 
 * This program is an example from the book "Internet 
 * programming with Java" by Svetlin Nakov. It is freeware. 
 * For more information: http://www.nakov.com/books/inetjava/ 
 */ 
import java.io.*; 
import javax.servlet.*; 
import javax.servlet.http.*; 
 
public class LoginServlet extends HttpServlet { 
    public void doGet(HttpServletRequest aRequest, 
        HttpServletResponse aResponse) 
    throws IOException, ServletException { 
        String username = aRequest.getParameter("username"); 
        String password = aRequest.getParameter("password"); 
        PrintWriter out = aResponse.getWriter(); 
        if ((username==null) || (password==null)) { 
            showLoginForm("Please login:", out); 
        } else if (username.equals(password)) { 
            HttpSession session = aRequest.getSession(); 
            session.setAttribute("USER", username); 
            aResponse.sendRedirect("main"); 
        } else { 
            showLoginForm("Invalid login! Try again:", out); 
        } 
    } 
 
    public void doPost(HttpServletRequest aRequest, 
        HttpServletResponse aResponse) 
    throws IOException, ServletException { 
        doGet(aRequest, aResponse); 
    } 
 
    private void showLoginForm( 
            String aCaptionText, PrintWriter aOutput) { 
        aOutput.println( 
            "<html><title>Login</title><body>\n" + 
            "<form method='POST' action='login'>\n" + 
            aCaptionText + "<br>\n" + 
            "<input type='text' name='username'><br>\n" + 
            "<input type='password' name='password'><br>\n" + 
            "<input type='submit' value='Login'>\n" + 
            "</body></form></html>" 
        ); 
    } 
}
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