Ok I found the solution. maybe it help someone else in future
If you are using the old JSP 1.2 descriptor, defined by DTD ,for example web.xml
<!DOCTYPE web-app PUBLIC
"-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd" >
<web-app>
//...
</web-app>
The EL is disabled or ignored by default, you have to enable it manually, so that it will outputs the value store in the “msg” model.
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<%@ page isELIgnored="false" %>
</head>
<body>
${msg}
</body>
</html>
If you are using the standard JSP 2.0 descriptor, defined by w3c schema ,for example web.xml
<web-app id="WebApp_ID" version="2.4"
xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
//...
</web-app>
The EL is enabled by default, and you should see the value stored in the “msg” model