为什么 ${bean.property} 在 JSP 中自动创建一个 bean？

Question

我知道 JSP 已被弃用。

Here,提到

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.

为了检查它是否真实，我想到了这个：

像这样的简单 JSP 页面，

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

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

哪里

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

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

它在命中时输出 http://localhost:8080/Leonard/faces/create.jsp:

Rafael Here

请推荐？

Answer 1

这条语句，

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

仅在您使用 JSF 1.1 或更早版本或使用 JSP 2.0 或更早版本时适用。从 JSF 1.2 和 JSP 2.1 开始，JSF EL 为 unified with JSP EL and that's why it started to work (via javax.el.CompositeELResolver).

尽管如此，不建议使用 ${...} 访问 JSF 托管 bean。它是不可写的，而 #{...} 是可写的，所以你真的需要在输入组件中使用 #{...} 。在同一个 JSF 页面中混合使用 ${...} 和 #{...} 可能最终会混淆未来的代码 readers/maintainers.

为什么 ${bean.property} 在 JSP 中自动创建一个 bean？

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

jsf

jsp

el

managed-bean