Returning multiple form errors

[KingdomX]

The idea:
A user fills a form and it goes through several checks on server side after a form submit. Let's say we have 4 different checks from the form:
1 - Checks the password pattern.
2 - Checks the password length.
3 - Checks the password for invalid characters like ⌐ or ☼.
4 - Checks if both password fields match

Let's say that all of these checks HAVE failed, so then we must return the user to the form and inform the checks he has failed on.

The problem:
I'm currently using the session to return the value to the form through an error string. But this will just be hell to manage. Suppose the user leaves the page... i'll have to unset that session, if i don't, he could click on a link to go to the form and it would display the errors all over again.

The code:

        String errors = "";
        // Checks the user's e-mail pattern
        if ( SecureInputs.patternEmail(mail1) ){
            errors += "<li> {invalidEmail}</li>"; 
        }
        // Checks if both e-mail fields match
        if ( SecureInputs.areEmailsDifferent(mail1, mail2) ){
            errors += "<li> {emailFieldsDontMatch}</li>"; 
        }
        // Checks the user's password pattern
        if ( SecureInputs.patternPassword(pw1) ){
            errors += "<li> {passwordInvalidCharacter}</li>"; 
        }
        // Checks the user's password length
        if ( SecureInputs.passwordLength(pw1) ){
            errors += "<li> {passwordBelowLength}</li>"; 
        }
        // Checks if both password fields match
        if ( SecureInputs.arePasswordsDifferent(pw1, pw2) ){
            errors += "<li> {passwordFieldsDontMatch}</li>"; 
        }
        // Checks if the user has agreed to the privacy terms
        if ( this.agreeCheck(agree) ){
            errors += "<li> {doesntAgreeTerms}</li>"; 
        }

        
        // If any errors were found, redirects the user back to the form
        if( !"".equals(errors) ){
            Session.session.setAttribute("errors", errors);
            Main.redirect(Main.registerPageLoc);
        }

I could really use some ideas on how to do this. I've been searching this for two days and couldn't find a way to return this to the form.

Thanks in advance!

[Eranga]

In such situation what I am doing is simply use a URL parameter. On the login page load validate the parameter and display the relevant message. Reason was, as you feel, managing the sessions is quite difficult in most of the situations.