尚硅谷JavaWeb笔记——Cookie（一文读懂什么是Cookie技术）

深碍√TFBOYSˉ_ 2022-11-01 10:58 201阅读 0赞

### 文章目录 ###

*  Cookie饼干
 *   *  Cookie简介
     *  Cookie有关操作
     *   *  Cookie的创建
         *  Cookie的获取
         *  Cookie值的修改
     *  Cookie的生命周期
     *  练习：免用户名登陆

# Cookie饼干 #

## Cookie简介 ##

**什么是Cookie？**

答：Cookie是服务器同志客户端保存键值对的一种技术，客户端有了Cookie后，每次请求都会发送给服务器。每个Cookie的大小都不能超过4kb。

## Cookie有关操作 ##

### Cookie的创建 ###

Cookie的创建流程如下所示

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说明：Cookie是服务器中**Servlet程序创建**并通过`response`返回给客户端浏览的的键值对信息。在服务器中需要执行**两个关键的操作**：

//1 创建Cookie对象
    Cookie cookie = new Cookie("key0", "v0");
    Cookie cookie1 = new Cookie("key1", "v1");
    Cookie cookie2 = new Cookie("key2", "v2");
    //2 通知客户端保存Cookie
    response.addCookie(cookie);
    response.addCookie(cookie1);
    response.addCookie(cookie2);
    response.getWriter().write("Cookie 创建 ");

如果不执行`response.addCookie(cookie)`，浏览器将无法知道服务器创建了cookie，可以在浏览器的检查中查看到Cookies信息

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### Cookie的获取 ###

cookie获取的流程图

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服务器获取客户端的Cookie只需要一行代码

protected void getCookie(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
      Cookie[] cookies = request.getCookies();
    
      Cookie iWannaCookie = CookieUtils.findCookie("key1", cookies);}
    
    // 如果不等于null，说明赋过值，也就是找到了需要的Cookie
    if (iWannaCookie != null) { 
      response.getWriter().write("OK 找到了！cookie : " + iWannaCookie.getName() + " = " + iWannaCookie.getValue() + "<br/>");
    
    }
    }

**查找cookie工具类**

public class CookieUtils { 
      /** * 查找指定名称的Cookie对象 * @param name * @param cookies * @return */
      public static Cookie findCookie(String name, Cookie cookies[]) { 
        if (name == null || cookies == null || cookies.length == 0) { 
          return null;
        }
        for (Cookie cookie: cookies) { 
    			// 如果找到了cookie
          if (name.equals(cookie.getName())) { 
            return cookie;
          }
        }
        return null;
      }
    }

### Cookie值的修改 ###

**方案一：（创重名再发送）**

1.  先**创建一个要修改的同名**的Cookie对象
2.  在构造器，同时赋予新的**Cookie值**
3.  调用`response.addCookie(Cookie);`

**方案二：（找目标重复值）**

1.  先查找到需要修改的Cookie对象
2.  调用`setValue()`方法赋予新的Cookie值
3.  调用`response.addCookie()`通知客户端保存修改

protected void updateCookie(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
      //方案一：
      //1、先创建一个要修改的同名的Cookie对象
      //2、在构造器，同时赋于新的Cookie值。
      Cookie cookie = new Cookie("key1","newValue1");
      //3、调用response.addCookie( Cookie ); 通知 客户端 保存修改
      resp.addCookie(cookie);
    
      //方案二：
      //1、先查找到需要修改的Cookie对象
      Cookie cookie = CookieUtils.findCookie("key1", request.getCookies());
      if (cookie != null) { 
        //2、调用setValue()方法赋于新的Cookie值。
        cookie.setValue("newV1");
        //3、调用response.addCookie()通知客户端保存修改
        response.addCookie(cookie);
      }
      response.getWriter().write(" ok方案2 ");
    }

⚠️ cookie**值不支持符号以及中文**

## Cookie的生命周期 ##

Cookie的声明控制是指如何管理Cookie什么时候被删除

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**设置Cookie生命周期为默认值**

/** * 默认的会话级别的Cookie * @param request * @param response * @throws ServletException * @throws IOException */
    protected void defaultLifeCookie(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
      Cookie cookie = new Cookie("d1", "d1v1");
    
      cookie.setMaxAge(-1);//设置存活时间
    
      response.addCookie(cookie);
    
    }

**设置Cookie生命周期为立即删除**

/** * 马上删除一个Cookie * @param request * @param response * @throws ServletException * @throws IOException */
    protected void deleteNowCookie(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
      // 先找到你要删除的Cookie对象
      Cookie cookie = CookieUtils.findCookie("key1", request.getCookies());
      if (cookie != null) { 
        // 调用setMaxAge(0);
        cookie.setMaxAge(0);// 表示马上删除，都不需要等待浏览器关闭
      }
      // 调用response.addCookie(cookie);
      response.addCookie(cookie);
      response.getWriter().write("删除 k1 ");
    }

**设置Cookie生命周期为一个小时**

/** * 设置存活1个小时的Cooie * @param request * @param response * @throws ServletException * @throws IOException */
    protected void life3600Cookie(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
      Cookie cookie = new Cookie("life", "life3600");
    
      cookie.setMaxAge(60 * 60);// 设置Cookie一小时之后被删除。无效
      response.addCookie(cookie);
      response.getWriter().write("已经创建了一个存活一小时的Cookie");
    }

**Cookie有效路径Path的设置**

Cookie的path属性可以有效的过滤**那些Cookie可以发给服务器，那些不发**。path属性是通过**请求的地址来进行有效过滤**

protected void pathCookie(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
      Cookie cookie = new Cookie("path1", "pathCookie1");
      // getContextPath() ===>>>> 得到工程路径
      cookie.setPath(request.getContextPath() + "/abc");// ===>>>> /工程路径/abc
      response.addCookie(cookie);
      response.getWriter().write("创建了一个带有Path路径的Cookie");
    }

## 练习：免用户名登陆 ##

免用户名登陆的细节原理及细节

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类加载失败的可能的原因

1.  web.xml出问题（过滤器+路径写错）
2.  tomcat以及javaEE版本不匹配
3.  artifacts中数据缓存，删除artifacts并重新添加

[img-W2SpLNFO-1614148377982_Users_gaojunsong_Library_Application Support_typora-user-images_Java_JAVAWeb_image-20210219102353603.png]: /images/20221024/17a8d86a6d034778b75185b519db8864.png
[img-wqRsp2EC-1614148377984_Users_gaojunsong_Library_Application Support_typora-user-images_Java_JAVAWeb_image-20210219103111791.png]: /images/20221024/913c40a570644b8ab9311c7acbf7ddc0.png
[img-KHs9nsfA-1614148377985_Users_gaojunsong_Library_Application Support_typora-user-images_Java_JAVAWeb_image-20210219104629282.png]: /images/20221024/a7365a0587ce4ec698207bfc6b0e0b7f.png
[img-eHOCBbDH-1614148377987_Users_gaojunsong_Library_Application Support_typora-user-images_Java_JAVAWeb_image-20210219105404934.png]: /images/20221024/0def9102b0e94dd6a81d3e8a1152c961.png
[img-zJ7bSisG-1614148377988_Users_gaojunsong_Library_Application Support_typora-user-images_Java_JAVAWeb_image-20210219111623848.png]: /images/20221024/7b1a91d837a943acaaae4da0f578f52a.png