如何在servlet完成其工作时设置中间(等待/处理)页面

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/waitingPage")
public class WaitingPageServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        request.getRequestDispatcher("waiting.jsp").forward(request, response);
    }

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

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/processingPage")
public class ProcessingPageServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 处理请求的逻辑
        request.setAttribute("result", "处理结果");
        request.getRequestDispatcher("processing.jsp").forward(request, response);
    }

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

<web-app>
   <servlet>
       <servlet-name>WaitingPageServlet</servlet-name>
       <servlet-class>com.example.WaitingPageServlet</servlet-class>
    </servlet>
   <servlet>
       <servlet-name>ProcessingPageServlet</servlet-name>
       <servlet-class>com.example.ProcessingPageServlet</servlet-class>
    </servlet>
   <servlet-mapping>
       <servlet-name>WaitingPageServlet</servlet-name>
        <url-pattern>/waitingPage</url-pattern>
    </servlet-mapping>
   <servlet-mapping>
       <servlet-name>ProcessingPageServlet</servlet-name>
        <url-pattern>/processingPage</url-pattern>
    </servlet-mapping>
</web-app>