We have a form at client side. When user fills the details and clicks on submit button then the rest api called which process the data and stored in database. Now what I want is user should redirect (POST method) to third party payment gateway page from server itself with required parameters, also I don't want to use query parameter string because its visible to user. I know there are two ways of doing it,

1. Using sendRedirect method :

   For redirection I used resp.sendRedirect("paymentgateway url"); but the problem with redirect method is that the post parameters are not sent to payment gateway.

2. Posting form with hidden fields :

   The payment gateway redirection should be done via posting form with hidden fields but I don't know how to do it at controller level.

<form method="post" action="paymentgateway url">
    <input type="hidden" name="txnid" value="98765">
    <input type="hidden" name="amt" value="100">
</form>

Also I want to show the user loading page after he clicks submit button.

Any help will be appreciated!