Servlet和jsp中跨应用的Session怎么取？

注意跨应用的Session是取不出来的。我的应用是ServletHello，第二个应用名字叫CookieTest，你可以观察到QueryCookie这个Servlet已经运行了，但就是Session取不出来。可以考虑用文件、数据库，URL传值、隐藏表单传递session id等。初学者不必关心。
package com;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;
public class ServletHello2 extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        HttpSession hs=request.getSession();
        hs.setAttribute("isLogin", "true");
        response.sendRedirect("http://localhost:8080/CookieTest/QueryCookie");
    }
}

package com;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class QueryCookie extends HttpServlet {
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        HttpSession hs=request.getSession();
        System.out.println("isLogin in Cookie Test Project is "+ hs.getAttribute("isLogin"));
    }
}
 

输出结果是：

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