Can <jsp:useBean> use an EL variable in id attribute?

Posted on 2004-09-06
Medium Priority
Last Modified: 2013-11-24

I'm no expert at either JSP or JSTL, but I'm trying to make my JSP scriptlet free.

Anyway, I'm trying to send a javabean from a servlet to a jsp page using the MVC pattern. The problem I'm having is on the JSP page. I'm running servlet version 2.3, JSP 1.2 and JSTL 1.0 on Tomcat 4.1.30.

I have a servlet that looks something like this:

package test;


public class MainServlet extends HttpServlet {
    public static final String NAME = "beanname";

    public void doGet(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {
    StringBean bean = new StringBean();
    bean.setText("Servlet set text");
    req.setAttribute(NAME, bean);
    RequestDispatcher d = req.getRequestDispatcher("/Main.jsp");
    d.forward(req, resp);

Notice the public static javabean name constant. I want to use this constant in my JSP, and that's my problem.

In my JSP I do something like this:

<%@ taglib uri="http://java.sun.com/jstl/core" prefix="c" %>

<c:set var="myvar">

<jsp:useBean id="${myvar}" class="test.StringBean" scope="request">
  For debugging: Bean created in jsp<br />


Text: <jsp:getProperty name="${myvar}" property="text" />

The trouble is that the compiler useBean's id attribute won't accept the EL variable. I get

    JavaCompile: Syntax error on token "{", ";" expected.

How can I refer to the Servlet constant name in useBean using JSTL/EL? Is there a better way (but not using scriptlets)?
Question by:boomerang061797
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LVL 11

Accepted Solution

sompol_kiatkamolchai earned 200 total points
ID: 11988364
It does not accept run-time expression. since it has to pre-compile to servlet.

If you define
<jsp:useBean id="${myvar}" class="test.StringBean" scope="request">
  For debugging: Bean created in jsp<br />

when servlet container compiler, how servlet container declare variable????

test.StringBean ${myvar} = new test.StringBean();

It is left-value, So it cannot run-time value.
LVL 11

Expert Comment

ID: 11988374
I think it's not important whatever the name is because it's used locally in jsp file.

Author Comment

ID: 11991038
Yes, the name isn't really important however I was trying to have the servlet be in charge of naming the bean. I the servlet should want to change the variable name then I wanted the JSP code to automatically be updated to use the new name.
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LVL 11

Expert Comment

ID: 11991101
It's left value. It cannot change after your jsp translate to servlet code.

Author Comment

ID: 11994795
Ok - so what you're saying is that the id can never be a EL expression or a scriptlet?
LVL 11

Expert Comment

ID: 11994823
Yes. That's right.

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