Q題目

要求：

顯示上次訪問頁面時間，並新增清除Cookie功能

如下圖：

清除Cookie

A 程式碼

實現Cookie顯示上次訪問時間

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;
/**
 *說明：
 *1.該方式將時間直接以long型別存進Cookie
 *2.從Cookie中取出值後，需要先做日期格式化，才能展示
 *
 *優點：避免某些電腦瀏覽器因為Cookie值儲存長短限制不能顯示上次訪問時間
 *
 *比如：“2017-05-04 20:33:22”,日期轉為該格式後，不能存進Cookie中，因為Cookie長度限制
 *   但直接以--時間戳（long型別）--的方式，可以直接存進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 {
        //編碼格式
        response.setContentType("text/html;charset=utf-8"
 
);
        PrintWriter writer=response.getWriter();

        writer.write("上次訪問時間：");

        Cookie[] cookies=request.getCookies();
        if(cookies!=null){
            //遍歷cookies，取出lastAccessTime這個cookie
            for (int i = 0; i < cookies.length; i++) {
                Cookie c=cookies[i];
                if("lastAccessTime".equals(c.getName())){
                    //取值上次訪問時間，並顯示出來
                    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>");

        //獲取當前時間，並存儲到Cookie中
        Long currentTime=System.currentTimeMillis();
        Cookie cookie=new Cookie("lastAccessTime", currentTime.toString());
        cookie.setMaxAge(5*60);//設定Cookie有效時間，5min內關閉再開啟瀏覽器Cookie會一直存在
        response.addCookie(cookie);

    }

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

}

清除Cookie

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;

/**
 * 說明：
 *      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時，完全沒必要先將cookie遍歷出來，再去清除cookie，儘管下面的方法可以實現清除cookie
        //我們可以根據cookie的特性，名字相同的cookie，後面設定的值會覆蓋前面的值
        /*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);
    }

}