ModelAndView’s model value is not displayed in JSP via EL-null-星河码客

Problem

In Spring MVC development, developer try to set a value into a model, and display the value in JSP via EL, e.g ${msg}, but it just outputs the result as it is – ${msg}, not the “value” stored in the model. The EL is just not working in JSP, why?

Spring’s Controller

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.AbstractController;

public class ABCController extends AbstractController{

	@Override
	protected ModelAndView handleRequestInternal(HttpServletRequest request,
		HttpServletResponse response) throws Exception {

		ModelAndView model = new ModelAndView("HelloWorldPage");
		model.addObject("msg", "hello world");
		
		return model;
	}
	
}

JSP page

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<body>
             ${msg}
</body>
</html>

Solution

This is the common asked question in the most Spring MVC hello world example. Actually it’s caused by the old JSP 1.2 descriptor.

1. JSP 1.2

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>

2. JSP 2.0

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, which is “hello world”.

This is my code to fix the problem:

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.1" 
	     xmlns="http://xmlns.jcp.org/xml/ns/javaee" 
	     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
	     xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee 
	     http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd">
	<display-name>Archetype Created Web Application</display-name>
	
......
	
</web-app>

Reference

Write JSP code that uses the directives