Java 如何从包含的servlet请求属性中获取servlet请求属性？

我在一个servlet中有以下代码：

dispatcher = request.getRequestDispatcher("LoginModel");
dispatcher.include(request, response);
if ((boolean) request.getAttribute("Successful")) {}

在第二个servlet中：

request.setAttribute("Successful", true);

---

但是，我在

请求中不断收到
NullPointerException
。getAttribute（“成功”）

代码执行此操作的唯一原因是没有调用您的

LoginModel

servlet（顺便说一句，您调试过它以进行检查吗？）

之所以出现

NullPointerException

，是因为您试图将null引用强制转换为

boolean

（安全检查可以解决此问题，但不会解决调用本身）

请参见一个正常工作的示例：

Servlet 1:

@WebServlet(urlPatterns = "/serv")
public class Serv extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        RequestDispatcher dispatcher = request.getRequestDispatcher("serv2");
        dispatcher.include(request, response);
        if (request.getAttribute("Successful") != null
                && (boolean) request.getAttribute("Successful")) {
            System.out.println("Success!");
        } else {
            System.out.println("No success!");
        }
    }
}

@WebServlet(urlPatterns = "/serv2")
public class Serv2 extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        request.setAttribute("Successful", true);
    }
}

Servlet 2:

@WebServlet(urlPatterns = "/serv")
public class Serv extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        RequestDispatcher dispatcher = request.getRequestDispatcher("serv2");
        dispatcher.include(request, response);
        if (request.getAttribute("Successful") != null
                && (boolean) request.getAttribute("Successful")) {
            System.out.println("Success!");
        } else {
            System.out.println("No success!");
        }
    }
}

@WebServlet(urlPatterns = "/serv2")
public class Serv2 extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        request.setAttribute("Successful", true);
    }
}

最终结果：

Success!

---

第二个servlet的url映射是否为

LoginModel

？@Arvind yes it isHi，似乎是第二个servlet中的一个捕获导致了NPE，现在刚刚解决了捕获发生的原因！