sendRedirect with passing some values.

[Vinoth Thirunavukarasu]

Hi,
I'm using a servlet to check whether the userName and password are exist if it is false I have to redirect to the login page with some message like "Invalid user name or password".
Now I used session.setAttribute("error",msg);
Is there any other way to pass error message to login page.

[Bauke Scholtz]

You can use a request parameter for that. You can just do a forward instead of redirect.

[Steve Luke]

You can pass the error to the next page as a url parameter:
String url = "/login?error="+URLEncoder.encode("Invalid Username or Password", "UTF-8");
The URLEncoder is needed to encode spaces so they don't break the URL.

A way to make passing the parameter easier is to store the possible errors in a central location with a lookup table. You would use a basic lookup value (like an integer) as a key for the lookup value, which simplifies the URL from:
/login?error=Invalid+Username+or+Password
to
/login?error=1

Here is an example below. Note that I don't have the webapp where I used this with me and I haven't done servlet/jsp programming in a few months so I am likely making mistakes, so take it as a guideline.

Central store for the error messages

package net.thelukes.store;
 
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
 
public enum WebUIErrors {
LoginError("Invalid Username or Password"),
MissingLink("The resource requested can not be found."),
AccountLocked("Your login has been blocked by the administrator (perhaps because "+
"of too many failed login attempts).  Please contact your administrator for help")
//...
;
private final String message;
WebUIErrors(String msg) {
this.message = msg;
}
public String getMessage() {
return message;
}

/**
 * The error map will let us store the errors in an easy lookup for contexts
 * where using enums isn't so easy, like in JSPs where you can use EL to 
 * lookup in a map, but not get enums easily.
 */
private static final Map<Integer, String> errorMap;
static {
Map<Integer, String> temp = new HashMap<Integer, String>();
WebUIErrors[] errors = WebUIErrors.values();
for (WebUIErrors error : errors) {
temp.put(error.ordinal(), error.message);
}
errorMap = Collections.unmodifiableMap(temp);
}
public static Map<Integer, String> getErrorMap() {
return errorMap;
}
}

Somewhere early in the webapp, like a context listener

            servletContext.setAttribute("errorMap", WebUIErrors.getErrorMap());

In the Servlet that detects the error and does the forward

            String url = "/login?error="+WebUIErrors.LoginError.ordinal();
            response.sendRedirect(url);

In the JSP that displays the login form:

            <div class="error">${errorMap[params.error]}</div>

[ December 19, 2008: Message edited by: Steve Luke ]

[Knaresh Gupta]

Hello you can simple write the HTML Code in else part like this
out.println("<li><i>we con't find the username/password provided by you</i></li>");
return;

it simply display the message in browser and automatically come back.