404 error in servlets

Question

It's my first day trying servlets. It's just a simple login function, but I get an error that doesn't explain what I'm doing wrong. It just says

404: The requested resource is not available.

Here's my servlet:

public class Login extends HttpServlet {
    private static final long serialVersionUID = 1L;

    public Login() {
        super();
    }

    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();
        String key = "ole";
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        response.sendRedirect("NewFile.jsp");
        if (session.getAttribute(username).equals(key)
                && session.getAttribute(password).equals(key)) {
            response.sendRedirect("secret.jsp");
        } else {
            response.sendRedirect("NewFile.jsp");
        }
    }

    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
    }

}

And here's my login page:

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Login page</title>
</head>
<body>

    Enter username and password below.
    <form method=get action="hej">
        <input type="text" user="username" /> <input type="password"
            user="password" /> <input type="submit" value="Login" />
    </form>
</body>
</html>

There is a file called secret.jsp as well, but there's nothing interesting in there. I don't understand why it's returning 404. When I have remove the if statement it works... only then, there's not much function.

What is the address displayed in the address bar when you get that 404? — JB Nizet, Nov 13 '14 at 18:50
A wrong name! So I learned that. It still gives me a NullPointerException at my if statement. I can't see what I'm not providing... — Rasmus, Nov 13 '14 at 18:52
The stack trace tells you that. Read it. And post it if you don't understand it. Note that `` doesn't have any `user` attribute. It has a `name` attribute though. — JB Nizet, Nov 13 '14 at 18:56
Make sure all your filenames are correct, and what the heck is `hej` — James Parsons, Nov 13 '14 at 19:19

score 2 · Answer 1 · answered Nov 14 '14 at 05:48

As you say it works without IF-ELSE then I guess your web.xml entry is correct.

First change this to

<input type="password" user="password" />

this

<input type="password" name="password" />

input tag does not have any user attribute , it's name.

Next mistake is , you are using session.getAttribute to access parameters that you have not set, yet.

Your code should be

if (username.equals(key)
        && password.equals(key)) {
    response.sendRedirect("secret.jsp");
} else {
    response.sendRedirect("NewFile.jsp");
}

session.getAttribute can only be used when you have in your code session.setAttribute example session.setAttribute("username","ole");session.setAttribute("password","ole");.

Then only you could get a value with session.getAttribute("username") OR session.getAttribute("password"). But right now it only returns NULL. So code won`t work.

You could add this code in your existing code and it will work.

session.setAttribute(username,username);
session.setAttribute(password,password);

Your complete code should be

String username = request.getParameter("username");
String password = request.getParameter("password");
session.setAttribute(username,username);
session.setAttribute(password,password);

//response.sendRedirect("NewFile.jsp");

if (session.getAttribute(username).equals(key)
        && session.getAttribute(password).equals(key)) {
    response.sendRedirect("secret.jsp");
} else {
    response.sendRedirect("NewFile.jsp");
}

I tried it out, I learned a lot from the post, however I still get a NullPointerException at the if. I also dont understand why it's not .setAttribute("username", username); ... you take the parameter from the .jsp file, yes? — Rasmus, Nov 14 '14 at 11:59
@Rasmus why it's not .setAttribute("username", username); because you are accessing the attributes as session.getAttribute(username) not session.getAttribute("username"). For getting NULL at IF , either the value returned by getAttribute is NULL OR the attribute is not present. Can you provide your updated code — Anurag Anand, Nov 16 '14 at 04:04
@Rasmus You can use session.getAttribute("username") if you set the attributes like this session.setAttribute("username", username);. Key should be matching. — Anurag Anand, Nov 16 '14 at 04:05
@Rasmus you should also check if username or password are not NULL , before setting them as attributes. — Anurag Anand, Nov 16 '14 at 06:18

score 0 · Answer 2 · answered Nov 13 '14 at 21:45

0

Replace user="... by name="... in your HTML and it will work.

answered Nov 13 '14 at 21:45

Romeo Kienzler

3,373
3
36
58

score 0 · Answer 3 · answered Nov 13 '14 at 21:49

0

Replace user="... by name="... in your HTML and it will work. NullPointerException is thrown because because of the wrong HTML the request parameters are NULL and these are used for the session lookup.

answered Nov 13 '14 at 21:49

Romeo Kienzler

3,373
3
36
58

404 error in servlets

3 Answers3