技術標籤：cookieservletsessionjava

package com.CookieDemo;

import com.utils.CookieUtils;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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.text.SimpleDateFormat;
import java.util.Date;

@WebServlet(name = "ServletCookieDemo",urlPatterns="/4")
public class ServletCookieDemo extends HttpServlet {
    protected void doPost(HttpServletRequest request,
 
 HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//        response.setContentType("text/html;charset=UTF-8");
 

//        response.getWriter().println("你好，歡迎來到本網站1");
        Cookie[] cookies =request.getCookies();
        Cookie cookie= CookieUtils.findCookie(cookies,"a");
        if(cookie == null){
            response.setContentType("text/html;charset=UTF-8");
            response.getWriter().println("你好，歡迎來到本網站");
        }else{
            String value = cookie.getValue();
            response.setContentType("text/html;charset=UTF-8");
            response.getWriter().println("你好，歡迎來到本網站,你上次的訪問時間為"+value+"");
        }
        String currentTime = new SimpleDateFormat("yyyy-M-d:hh:mm:ss").format(new Date());
        Cookie c=new Cookie("a",currentTime);
        response.addCookie(c);

    }
}

package com.utils;

import javax.servlet.http.Cookie;

/**
 * 查詢指定名稱Cookie的工具類
 */
public class CookieUtils {
    public static Cookie findCookie(Cookie[] cookies,String name){
        if(cookies==null){
            return null;
        }else {
            for(Cookie cookie:cookies){
                if(name.equals(cookie.getName())){
                    return cookie;
                }
            }return null;
        }
    }
}

實驗了一個上午終於成功了，導致失敗的原因是因為2點：
第一，在Utils工具類中，分以下情況去討論：
1.瀏覽器中沒有cookies；
2.瀏覽器中有cookie；
-2.1與給定的cookie同名
-2.2與給定的cookie不同名
在2.2這種情況下不小心將return寫到{}外面,導致最終結果怎麼樣都是null。
第二，用了過時的toLocalString()方法