1. Cookie基本使用

过程：
当浏览器发出请求1给服务器端A时，A Servlet就会创建一个cookie对象数据，A在做响应时，就会发送给浏览器，浏览器就把cookie保存在内存之中；
当浏览器在同一次会话中，再次发送请求时，就会携带cookie访问B Servlet，而B就可以访问到cookie中的数据。

1.1 发送cookie

创建AServlet

@WebServlet("/aServlet")
public class AServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //发送Cookie

        //1. 创建Cookie对象
       	Cookie cookie = new Cookie("username","zs");

        //2. 发送Cookie，response
        response.addCookie(cookie);
    }

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

启动服务器在谷歌中查询cookie

1.2 获取cookie

创建BServlet

@WebServlet("/bServlet")
public class BServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取Cookie

        //1. 获取Cookie数组
        Cookie[] cookies = request.getCookies();

        //2. 遍历数组
        for (Cookie cookie : cookies) {
            //3. 获取数据
            String name = cookie.getName();
            if("username".equals(name)){
                String value = cookie.getValue();
                //URL解码
                value = URLDecoder.decode(value,"UTF-8");
                
                System.out.println(name+":"+value);

                break;
            }
        }

    }

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

访问AServlet之后，继续访问BServlet，控制台输出

2. cookie原理及细节

2.1 cookie原理

发送cookie，Tomcat服务器是基于HTTP协议的，放的是HTTP的响应数据，当服务器发现是发送cookie数据时，Tomcat就在响应数据中加了一个响应头set-cookie，然后浏览器接收并解析，获取数据存储至内存。
当浏览器同一会话中再次访问时，携带cookie访问BServlet，浏览器会自动加请求头cookie，然后BServlet获取请求头数据，然后通过request对象，把所有的数据获取出来。

2.2 cookie细节

2.2.1 cookie的存活时间

@WebServlet("/aServlet")
public class AServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //发送Cookie

        //1. 创建Cookie对象
        Cookie cookie = new Cookie("username","zs");
        
        //设置存活时间   ，1周 7天
        cookie.setMaxAge(60*60*24*7);

        //2. 发送Cookie，response
        response.addCookie(cookie);
    }

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

2.2.2 cookie存储中文

cookie中不能直接使用中文，需要进行URL编码再解码

@WebServlet("/aServlet")
public class AServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //发送Cookie
        
        String value = "张三";
        //URL编码
        value = URLEncoder.encode(value, "UTF-8");
        System.out.println("存储数据："+value);
		//1. 创建Cookie对象
        Cookie cookie = new Cookie("username",value);

        //设置存活时间   ，1周 7天
        cookie.setMaxAge(60*60*24*7);

        //2. 发送Cookie，response
        response.addCookie(cookie);
    }

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

@WebServlet("/bServlet")
public class BServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取Cookie

        //1. 获取Cookie数组
        Cookie[] cookies = request.getCookies();

        //2. 遍历数组
        for (Cookie cookie : cookies) {
            //3. 获取数据
            String name = cookie.getName();
            if("username".equals(name)){
                String value = cookie.getValue();
                //URL解码
                value = URLDecoder.decode(value,"UTF-8");

                System.out.println(name+":"+value);

                break;
            }
        }

    }

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

先进行URL编码，这里还设置cookie的存活时间为一周

URL解码