为什么Servlet转发后，会回到原来Servlet继续执行输出语句？

为什么转发只有一次请求而Request对象在转发后发生了改变？

代码如下：

@WebServlet("/demo2")
public class ServletDemo2 extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

          System.out.println("demo2......第一次");
          System.out.println("demo2:"+request);
          request.getRequestDispatcher("/demo1").forward(request, response);
          System.out.println("demo2......第二次");
          System.out.println("demo2:"+request);

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

}

@WebServlet("/demo1")
public class ServletDemo1 extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

          System.out.println("demo1.......");
          System.out.println("demo1:"+request);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    this.doPost(request,response);
}

}

输出结果如下：

demo2......第一次
demo2:org.apache.catalina.connector.RequestFacade@4fb8968f
demo1.......
demo1:org.apache.catalina.core.ApplicationHttpRequest@1fdba35b
demo2......第二次
demo2:org.apache.catalina.connector.RequestFacade@4fb8968f