你可以用测试HttpServletRequest#getSession(boolean create)用create=false。如果尚未创建，它将返回null。

HttpSession session = request.getSession(false);
if (session == null) {
    // Session is not created.
} else {
    // Session is already created.
}

如果您实际上确实想创建会话（如果它不存在），那么只需抓住它并使用HttpSession#isNew()以下命令测试新鲜度：

HttpSession session = request.getSession();
if (session.isNew()) {
    // Session is freshly created during this request.
} else {
    // Session was already created during a previous request.
}

那就是您在Servlet中要做的。在JSP中，您只能在JSTL和EL的帮助下测试新鲜度。您可以抓住会话PageContext#getSession()，然后再调用isNew()它。

<c:if test="${pageContext.session.new}">
    <p>Session is freshly created during this request.</p>
</c:if>

要么

<p>Session is ${pageContext.session.new ? 'freshly' : 'already'} created.</p>