我的JSP项目中有三个简单的HttpServlet类，即“ LoginServlet”，“ LogoutServlet”和“
ProfileServlet”。

• LoginServlet：通过将“名称”属性设置为会话来登录用户
• LogoutServlet：注销用户并使会话无效
• ProfileServlet：如果用户已登录，则显示用户欢迎信息

我认为以下两个最后两个servlet是有问题的。

@SuppressWarnings("serial")
public class LogoutServlet extends HttpServlet {
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            response.setContentType("text/html");
            PrintWriter out=response.getWriter();

            HttpSession session=request.getSession(false);
            session.invalidate();

            request.getRequestDispatcher("link.jsp").include(request, response);

            out.print("You are successfully logged out!");

            out.close();
    }
}

和

@SuppressWarnings("serial")
public class ProfileServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        request.getRequestDispatcher("link.jsp").include(request, response);

        HttpSession session = request.getSession(false);
        if (session != null) {
            String name = (String) session.getAttribute("name");

            out.print("Hello, " + name + " Welcome to Profile");
        } else {
            out.print("Please login first");
            request.getRequestDispatcher("login.html").include(request,
                    response);
        }
        out.close();
    }
}

和link.jsp：

<% HttpSession nsession = request.getSession(false);
if(nsession == null) {
%>
<a href="login.html">Login</a>
<%
}
else {
%>
<a href="LogoutServlet">Logout</a>
<%
}
%>
<a href="ProfileServlet">Profile</a>
<hr/>

问题是用户登录时，单击“注销”链接并调用“ LogoutServlet”时，会话未正确无效，并且ProfileServlet仍打印出来

"Hello, null Welcome to Profile"

而不是重定向到“ login.html”页面，因为该会话仍不为null。结果，“登录”链接未显示在“ link.jsp”页面上。这使用户无法尝试再次登录。

编辑： 为了使问题得到澄清，我做了一个新的html页面并更新了servlet以执行此操作

request.getRequestDispatcher("link.html").include(request, response);

和“ link.html”。

<a href="login.html">Login</a>
<a href="LogoutServlet">Logout</a>
<a href="ProfileServlet">Profile</a>
<hr/>

有趣的是，这正是我想要的！我想问题是

request.getRequestDispatcher("link.jsp").include(request, response);

但是我无法解释为什么…