Cookie存储以前的值Servlet

Question

大家好我正在开发一个servlet，它使用以前存储的值来丢失参数。如果用户第一次访问该页面并且未输入任何值，则显示参数值的错误;我的问题是当值为null时它不显示错误。其次，我的cookie存储以前的值一次。例如，如果我输入缺失值，它将显示先前输入的值，但如果我连续执行，则第二次显示它将显示null。这是我的代码：

protected void service(HttpServletRequest request, HttpServletResponse          response) throws ServletException, IOException {
Cookie cookie1,cookie2,cookie3;
    String getfirst=request.getParameter("first");
    String getlast=request.getParameter("last");
    String getemail=request.getParameter("email");
    cookie1 = new Cookie("firstname", getfirst);
    cookie2 = new Cookie("lastname", getlast);
    cookie3 = new Cookie("email", getemail);
    cookie1.setMaxAge(3600);
    cookie2.setMaxAge(3600);
    cookie3.setMaxAge(3600);
    response.addCookie(cookie1);
    response.addCookie(cookie2);
    response.addCookie(cookie3);
PrintWriter out=response.getWriter();



Cookie[] cookies = request.getCookies();

if (cookies!=null) {
    Cookie ck;

    for (int i = 0; i < cookies.length; i++) {
        ck = cookies[i];
        out.println(ck.getName() + " "
                + ck.getValue());
    }}
     else{
        out.println("Unknown value");


}