记账本开发记录——第十六天（2020.2.3）

写在前面：关于昨天的问题，在发完博客后捣鼓了俩小时搞好了。顺带着基本问题也解决了，是因为时区问题，c3p0默认时间为美国时间，而我们的电脑都是中国时间，时区不一致就没法用（咱也不知道为啥），至于数据库存储数据乱码问题，在连接数据库时写好连接的编码，并且在后台写好编码就可将问题解决。可以看到配置可真是个令人上头的玩意...

今日的学习：今天学习了会话技术Cookie&Session。通过这两个会话技术，可以解决很多业务上的基本问题，如验证码的校验，不同的用户显示不同的界面，如不同人的购物车不同，就可以通过设置session进行实现。

首先是会话技术的概念：从打开一个浏览器访问某个站点，到关闭这个浏览器的整个过程，称为一次会话。可以看到会话的概念是比较广泛的。在会话技术中有两种：cookie和session，cookie存在于本地，session存在于服务器端，由此便可看出cookie是可以被本浏览器清除的（清理垃圾时候的选项），而session存在于服务端，也就加大了服务端的压力。

下面是关于cookie的创建和发送的demo:

package cookie;

import java.io.IOException;
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;

/**
 * Servlet implementation class SendCookieServlet
 */
@WebServlet("/Send")
public class SendCookieServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public SendCookieServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
        //1.创建cookie对象
        Cookie cookie = new Cookie("name", "liuge");
        //1.1 为cookie设置持久化时间-----存放在磁盘上的时间
        cookie.setMaxAge(60*10);//10分钟----时间设置为0代表删除cookie
        //1.2 为cookie设置携带的路径
        //cookie.setPath("/Day16/Send");//访问Send资源时才携带cookie
        //cookie.setPath("/Day16");//访问Day16下的所有资源都携带cookie
        //cookie.setPath("/");//访问目前tomcat下的所有的资源都携带cookie
        //2.将cookie中存储的信息发送到客户端——头
        response.addCookie(cookie);
        
        
    }

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

}

得到cookie的demo:

package cookie;

import java.io.IOException;
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;

/**
 * Servlet implementation class GetCookieServlet
 */
@WebServlet("/GetCookieServlet")
public class GetCookieServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public GetCookieServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
        //获得客户端携带的cookie数据
        Cookie[] cookies = request.getCookies();
        //通过cookie的名称获得想要的cookie
        for(Cookie cookie:cookies) {
            //获得cookie的名称
            String cookiename = cookie.getName();
            if(cookie!=null) {
               if(cookiename.equals("name")) {
                //获得该cookie的值
                String cookieValue = cookie.getValue();
                System.out.println(cookieValue);
            }
            }
        }
    }

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

}

根据cookie的特性，做了一个显示上回访问时间的demo:

package lastaccesstime;

import java.io.IOException;
import java.util.Date;
import java.text.SimpleDateFormat;

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 com.mysql.fabric.xmlrpc.base.Data;

/**
 * Servlet implementation class LastAccessTimeServlet
 */
@WebServlet("/LastAccessTime")
public class LastAccessTimeServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public LastAccessTimeServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获得当前时间
        Date date =new Date();
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd-hh:mm:ss");
        String currentTime = format.format(date);
        //1.创建cookie 记录当前的最新的访问时间
        Cookie cookie = new Cookie("lastAccessTime",currentTime);
        cookie.setMaxAge(60*10*500);
        response.addCookie(cookie);
        //2.获得客户端携带的cookie ----lastAccessTime
        String lastAccessTime = null;
        Cookie[] cookies = request.getCookies();
        if(cookies!=null) {
            for(Cookie coo:cookies) {
                if("lastAccessTime".equals(coo.getName())) {
                    lastAccessTime = coo.getValue();
                }
            }
        }
        response.setContentType("text/html;charset=UTF-8");
        if(lastAccessTime==null) {
            response.getWriter().write("您是第一次访问");
        }
        else {
            response.getWriter().write("您上次访问时间是:"+lastAccessTime);
        }
    }

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

}

需要注意的是，新版本的tomcat无法存储空格，cookie也无法存储中文。

之后是关于session的创建和发送demo:

package session;

import java.io.IOException;
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 javax.servlet.http.HttpSession;

/**
 * Servlet implementation class SessionServlet1
 */
@WebServlet("/SessionServlet1")
public class SessionServlet1 extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public SessionServlet1() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
        //创建该客户端(会话)的私有session区域
        /*request.getSession()方法内部会判断该客户端是否在服务器端已经存在session
         * 如果该客户端在此服务器不存在session 那么就会创建一个新的session对象
         * 如果该客户端在服务求已存在session 就会获得已经存在的该session返回
         */
        HttpSession session = request.getSession();
        
        session.setAttribute("name", "tom");
        String id = session.getId();//该session对象的id
        //手动创建一个存储JSESIONID的Cookie 为该cookie设置持久时间
        Cookie cookie = new Cookie("JSESSIONID", id);
        cookie.setPath("/Day16/");
        cookie.setMaxAge(60*10);
        response.addCookie(cookie);
        response.getWriter().write("JSESSIONID:"+id);
    }
    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

以及显示session的demo:

package session;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class SessionServlet2
 */
@WebServlet("/Session2")
public class SessionServlet2 extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public SessionServlet2() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
        //从session中获得存储的数据
        HttpSession session = request.getSession();
        String attribute = (String) session.getAttribute("name");
        response.getWriter().write(attribute);
    }

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

}

最后，根据session实现了一个验证码校验功能：

package login;

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

/**
 * Servlet implementation class Login
 */
@WebServlet("/Login")
public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public LoginServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
        //验证码的校验
        //获得页面输入的验证
        request.setCharacterEncoding("UTF-8");
        String checkCode_client = request.getParameter("checkCode");
        //获得生成图片的文字的验证码
        String checkCode_session = (String) request.getSession().getAttribute("checkcode_session");
        //将二者进行比对
        if(!checkCode_session.equals(checkCode_client)) {
            request.setAttribute("loginInfo", "您的验证码不正确");
            request.getRequestDispatcher("/login.jsp").forward(request, response);
            return;
        }
        
        //获得页面的用户名和密码进行数据库的校验
        //...
    }

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

}

今日总结:可以看到，通过cookie和session的使用，可以实现一些很简单的业务流程。日后也可在自己的网站中实现。