Cookie如何在servlet 中使用

package com.learn;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

/**
 * 
 */
public class CookieServlet extends HttpServlet {

 @Override
 protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  //cookie引用
  Cookie cookie = null;
  //设置返回类型为文本类型
  resp.setContentType("text/plain");
  //获取输出对象
  PrintWriter out = resp.getWriter();

  //从请求参数中获取cookies
  Cookie[] cookies = req.getCookies();
  if(cookies != null){
   for (int i = 0; i < cookies.length ; i++) {
    out.println("name:"+cookies[i].getName());
    out.println("value:"+cookies[i].getValue());
    //如果cookie值为user，则赋值给cookie
    if(cookies[i].getName().equals("user")){
     cookie = cookies[i];
    }
   }

  } else {
   out.print("no cookie");
  }

  if(cookie == null){
   cookie = new Cookie("user","tom");
   //设置cookie最大值为60分钟
   cookie.setMaxAge(60*60);
   resp.addCookie(cookie);
  } else if(cookie.getValue().equals("tom")){
   cookie.setValue("jack");
   resp.addCookie(cookie);
  } else if(cookie.getValue().equals("jack")){
   cookie.setMaxAge(0);
   resp.addCookie(cookie);
  }

  out.close();
 }

 @Override
 protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  super.doPost(req, resp);
 }
}

<servlet>
  <servlet-name>cookie</servlet-name>
  <servlet-class>com.learn.CookieServlet</servlet-class>
 </servlet>
 <servlet-mapping>
  <servlet-name>cookie</servlet-name>
  <url-pattern>/cookie</url-pattern>
</servlet-mapping>