In the jsp page you may define global js variable and access those variables from the external js like:
jsp file
<script>
myModel=[];
myModel.paramOne='${model.paramOne}';
myModel.paramTwo='${model.paramTwo}';
myModel.paramThree='${model.paramThree}';
</script>
All server side scripts been rendered at server side and those value will be hardcoded once rendered. Once page loaded in the browser, global variables will be created with the rendered hardcoded value. And my myModel can be access in the external file also.
EDIT: Here is the someJsp.jsp file
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<!DOCTYPE>
<html>
<head>
<script>
myModel=[];
myModel.paramOne='${model.paramOne}';
myModel.paramTwo='${model.paramTwo}';
myModel.paramThree='${model.paramThree}';
</script>
<script src="externalJs.js"></script>
</head>
<body>
<!--content-->
</body>
and externalJs.js
$(document).ready(function() {
// myModel will be accessible from here because it's globally declared
alert(myModel);
});