Cookie应用：显示上次访问页面时间

Q题目

显示上次访问页面时间，并添加清除Cookie功能

A 代码

package com.tcb.cookie;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
*说明：
*1.该方式将时间直接以long类型存进Cookie
*2.从Cookie中取出值后，需要先做日期格式化，才能展示
*
*优点：避免某些电脑浏览器因为Cookie值存储长短限制不能显示上次访问时间
*
*比如：“2017-05-04 20:33:22”,日期转为该格式后，不能存进Cookie中，因为Cookie长度限制
*   但直接以--时间戳（long类型）--的方式，可以直接存进Cookie
*/
public class CookieServlet01 extends HttpServlet {
private static final long serialVersionUID = 1L;

public CookieServlet01() {
super();
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//编码格式
response.setContentType("text/html;charset=utf-8");
PrintWriter writer=response.getWriter();

writer.write("上次访问时间：");

Cookie[] cookies=request.getCookies();
if(cookies!=null){
//遍历cookies，取出lastAccessTime这个cookie
for (int i = 0; i < cookies.length; i++) {
Cookie c=cookies[i];
if("lastAccessTime".equals(c.getName())){
//取值上次访问时间，并显示出来
String time=c.getValue();
time=new Date(Long.parseLong(time)).toLocaleString();
writer.write(String.valueOf(time));
}
}
}

writer.write("<a href="+request.getContextPath()+"/ClearCookieServlet>清除Cookie</a>");

//获取当前时间，并存储到Cookie中
Long currentTime=System.currentTimeMillis();
Cookie cookie=new Cookie("lastAccessTime", currentTime.toString());

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cookie.setMaxAge(5*60);//设置Cookie有效时间，5min内关闭再打开浏览器Cookie会一直存在
response.addCookie(cookie);

}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}

}

package com.tcb.cookie;

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

/**
* 说明：
*      清楚Cookie
*/
public class ClearCookieServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

public ClearCookieServlet() {
super();
}

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

//清除cookie时，完全没必要先将cookie遍历出来，再去清除cookie，尽管下面的方法可以实现清除cookie
//我们可以根据cookie的特性，名字相同的cookie，后面设置的值会覆盖前面的值
/*Cookie[] cookies=request.getCookies();
if(cookies!=null){
for (Cookie cookie : cookies) {
if("lastAccessTime".equals(cookie.getName())){
cookie.setMaxAge(0);
response.addCookie(cookie);
}
}
}*/

//便捷做法
Cookie cookie=new Cookie("lastAccessTime", "");
cookie.setMaxAge(0);
response.addCookie(cookie);

}

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

}