如何在 JSP EL 中检查会话? [英] How to check for session in JSP EL?

问题描述

如何检查EL中的请求是否存在会话?我正在尝试类似的东西:

How do you check if a session exists for the request in EL? I'm trying something like:

<c:if test="${pageContext.request.session != null}"> ... </c:if>

但它似乎永远不会为空.

but it seems like it's never null.

推荐答案

确实永远不会null.会话总是出现在 JSP EL 中，除非添加

It's indeed never null. The session is always present in JSP EL, unless you add

<%@page session="false" %>

到 JSP 的顶部.然后，您可以按如下方式检查会话(仅限 EL 2.2！):

to top of JSP. You could then check for the session as follows (EL 2.2 only!):

<c:if test="${pageContext.request.getSession(false) != null}">
    <p>The session has been created before.</p>
</c:if>

我不确定具体的功能要求是什么.如果您想检查会话是新会话还是已经创建，请使用 HttpSession#isNew().

I'm not sure what's the concrete functional requirement is. If you'd like to check if the session is new or has already been created, use HttpSession#isNew() instead.

<c:if test="${not pageContext.session['new']}">
    <p>You've already visited this site before.</p>
</c:if>
<c:if test="${pageContext.session['new']}">
    <p>You've just started the session with this request!</p>
</c:if>

(new 的大括号符号是强制性的，因为 new 是 Java 语言中的保留字面量)

(the brace notations for new are mandatory because new is a reserved literal in Java language)

如果您依赖于特定会话属性，例如设置为的登录用户

Of if you're relying on a specific session attribute, such as the logged-in user which is been set as

session.setAttribute("user", user);

那么你应该拦截它而不是:

then you should rather be intercepting on that instead:

<c:if test="${not empty user}">
    <p>You're still logged in.</p>
</c:if>
<c:if test="${empty user}">
    <p>You're not logged in!</p>
</c:if>

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