Why does ${bean.property} auto-creates a bean in JSP?

Question

I know JSP has been deprecated.

Here, it is mentioned that

In JSP, the ${} won't autocreate the managed bean when it's not in scope yet. You can thus only use it if you can guarantee that #{} on the very same managed bean is been used somewhere before in the component tree and also take view build time vs view render time lifecycle into account.

Just to check whether its true or not, I came up with this:

A simple JSP page like this,

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

            ${myPlayersBean.playerName}
            Here
        </body>
    </html>

where

@ManagedBean(name = "myPlayersBean")
@RequestScoped
public class PlayersBean {

    private String playerName = "Rafael";
    // getters & setters
}

it does outputs on hitting http://localhost:8080/Leonard/faces/create.jsp:

Rafael Here

Please suggest?

Which JSF impl/version? Behavior may have changed as compared to past. — BalusC, Mar 17 '16 at 11:16
@BalusC: Please edit it accordingly. http://stackoverflow.com/questions/1847751/what-is-the-difference-between-expr-and-expr-in-jsf-are-there-any-cases-w ; http://stackoverflow.com/questions/15526536/immediate-vs-deferred-evalutation-for-reading-bean-properties ; http://stackoverflow.com/questions/11733867/reading-bean-list-using-jstl-and-assigning-to-javascript-variable-in-facelets — Farhan stands with Palestine, Mar 17 '16 at 11:26
Which container impl/version? Did you enable CDI? I will only edit once I know and can explain the cause. I can assure this is never intented to work. At least, not during the Java EE 5 era. — BalusC, Mar 17 '16 at 11:44
Reproduced, nice find. Will look later for the Why. Wondering if the same happens with JSF 1.2. — BalusC, Mar 17 '16 at 11:58
I have updated the answers you linked/found. Thanks for pointing out this! — BalusC, Mar 19 '16 at 11:31

score 1 · Accepted Answer · edited May 23 '17 at 12:31

This statement,

In JSP, the ${} won't autocreate the managed bean when it's not in scope yet

is only applicable when you're using JSF 1.1 or older or when you're using JSP 2.0 or older. Since JSF 1.2 and JSP 2.1, JSF EL was unified with JSP EL and that's why it started to work (via javax.el.CompositeELResolver).

Nonetheless, using ${...} to access JSF managed beans is not recommended. It is not writable, while #{...} is writable so you really need to use #{...} in input components. Mixing ${...} and #{...} in same JSF page may end up to be confusing for future code readers/maintainers.

Why does ${bean.property} auto-creates a bean in JSP?

1 Answers1