JavaScript and JSP

I have 2 problems:
1. I am embedding JavaScript in JSP to check the value of a text box as following :
function Check()
{
var n =<%= Integer.parseInt((String)request.getAttribute("quantity"))%>
if(1 > n > 20)
alert(" Please enter valid number");
}
please let me know if this is the right way to embed the javascript.. and do java code need to be in <% --code-- %> in the aboce script. help would be greately appreciated.
2. when i click on the refresh button on the browser, it submits the form again. Is there a way so that form is not submitted on clicking refresh button.
looking forward to your help. .thanks

But then what is calling your function? Is there a reason you are not using plain javascript with the HTML form? Why not check the value of "quantity" before you process the page? You can use onSubmit or onClick with your form to check the value before submission.
As far as refreshing the page, if your page has already been submitted and what you are looking at is the results after returning from form processing, you are always going to resubmit the form on refresh. You'd have to use your back button to get back to the original form. Does that make sense or sound like babbling?
I hope this helps.