第74节：Java中的Cookie和Session

达达前端

发布于 2019-07-03 14:42:38

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发布于 2019-07-03 14:42:38

文章被收录于专栏：达达前端

第74节：Java中的Cookie和Session

`ServletContext`:

什么是ServletContext,有什么用哦，怎么用呢？

启动服务器后，会给每个应用程序创建一个ServletContext,并且这个ServletContext对象只有一个。可以用于获取全局参数，工程下的资源，和存取数据，共享数据。

例子，如何获取全局参数，如何获取工程下的资源，如何进行存取数据，用例子代码进行展示。

getServletContext().getInitParams();和getServletConfig().getInitParams();

getServletContext().getRealPath() getServletContext().getReasourceAsStream()

InputStream is = getClass().getClassLoader().getReasourceAsStream();

相对路径和绝对路径

getServletContext().setAttribute()

getServletContext().getAttribute()

获取登录成功次数

`HttpServletRequest`:

请求对象，用于封装客户端提交过来的数据或者信息。可以获取头信息，提交过来的数据： `request.getParameter("name"); // dashucoding url连接拼接

中文乱码情况

`HttpServletResponse`:

响应对象，服务器要返回给客户端的数据

跳转页面： response.setStatus(302);

response.setHeader("Location","success.html");

文件下载：输出流和输入流的对接

下载中文名字的资源：

效果

效果

// index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>

    默认servlet去下载<br>
    <a href="download/aa.jpg">aa.jpg</a><br>
    <a href="download/bb.txt">bb.txt</a><br>
    <a href="download/cc.rar">cc.rar</a><br>

    <br>手动下载<br>
    <a href="Demo01?filename=aa.jpg">aa.jpg</a><br>
    <a href="Demo01?filename=bb.txt">bb.txt</a><br>
    <a href="Demo01?filename=cc.rar">cc.rar</a><br>
    <a href="Demo01?filename=达叔.png">达叔.png</a><br>
</body>
</html>

// Demo01.java
package com.dashucoding.servlet;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Demo01
 */
public class Demo01 extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        // 获取要下载的文件名字
        String fileName = request.getParameter("filename");
        // 获取这个文件在tomcat里面的绝对路径地址
        String path = getServletContext().getRealPath("download/"+fileName);
        
        // 用于用户下载
        response.setHeader("Content-Disposition", "attachment; filename="+fileName);
        
        // 转化成输入流
        InputStream is = new FileInputStream(path);
        OutputStream os = response.getOutputStream();
        
        int len = 0;
        byte[] buffer = new byte[1024];
        while( (len = is.read(buffer)) != -1) {
            os.write(buffer, 0, len);
        }
        
        os.close();
        is.close();
        
    }

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

}

浏览器

// Demo01.java
package com.dashucoding.servlet;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLEncoder;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Demo01
 */
public class Demo01 extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        // 获取要下载的文件名字
        String fileName = request.getParameter("filename");
        
        // get请求有中文
        //byte[] bytes = fileName.getBytes("ISO-8859-1");
        //new String(bytes, "UTF-8");
        fileName = new String(fileName.getBytes("ISO-8859-1"), "UTF-8");
        System.out.println("fileName="+fileName);
        
        // 获取这个文件在tomcat里面的绝对路径地址
        String path = getServletContext().getRealPath("download/"+fileName);
        
        // 对中文的名字进行编码处理
        // 获取来访客户端的类型
        String clientType = request.getHeader("User-Agent");
        
        if (clientType.contains("Firefox")) {
            fileName = DownLoadUtil.base64EncodeFileName(fileName);
        }else {
            fileName = URLEncoder.encode(fileName, "UTF-8");
        }
        
        // 用于用户下载
        response.setHeader("Content-Disposition", "attachment; filename="+fileName);
        
        // 转化成输入流
        InputStream is = new FileInputStream(path);
        OutputStream os = response.getOutputStream();
        
        int len = 0;
        byte[] buffer = new byte[1024];
        while( (len = is.read(buffer)) != -1) {
            os.write(buffer, 0, len);
        }
        
        os.close();
        is.close();
        
    }

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

}

// DownLoadUtil
package com.dashucoding.servlet;

import java.io.UnsupportedEncodingException;

import sun.misc.BASE64Encoder;

public class DownLoadUtil {
    public static String base64EncodeFileName(String fileName) {
        BASE64Encoder base64Encoder = new BASE64Encoder();
        try {
            return "=?UTF-8?B?"
                    + new String(base64Encoder.encode(fileName
                            .getBytes("UTF-8"))) + "?=";
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }
}

效果

登录

效果

// LoginServlet
package com.dashucoding.servlet;

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

/**
 * Servlet implementation class LoginServlet
 */
public class LoginServlet extends HttpServlet {
    
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        // public void setContextType(String type)
        // 设置将发送到客户端的响应的内容类型,如果该响应尚未提交,给定内容类型可能包含字符编码规范,例如
        // text/html;charseet=UTF-8,如果在调用 getWriter之前调用此方法,则只根据给定内容类型设置响应的字符编码
        
        response.setContentType("text/html;charset=utf-8");
        
        String userName = request.getParameter("username");
        String password = request.getParameter("password");
        
        if("admin".equals(userName) && "123".equals(password)) {
            response.getWriter().write("登录成功");
        }else {
            response.getWriter().write("登录失败");
        }
        
    }

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

}

// web
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>RequestRedirctionDemo</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <description></description>
    <display-name>LoginServlet</display-name>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>com.dashucoding.servlet.LoginServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/login</url-pattern>
  </servlet-mapping>
</web-app>

// login
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>

    <form action="login">
        账号: <input type="text"  name="username"/><br>
        密码: <input type="text"  name="password"/><br>
        <input type="submit"  value="登录"/><br>
    </form>
</body>
</html>

效果

效果

效果

// LoginServlet
package com.dashucoding.servlet;

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

/**
 * Servlet implementation class LoginServlet
 */
public class LoginServlet extends HttpServlet {
    
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        // public void setContextType(String type)
        // 设置将发送到客户端的响应的内容类型,如果该响应尚未提交,给定内容类型可能包含字符编码规范,例如
        // text/html;charseet=UTF-8,如果在调用 getWriter之前调用此方法,则只根据给定内容类型设置响应的字符编码
        
        response.setContentType("text/html;charset=utf-8");
        
        String userName = request.getParameter("username");
        String password = request.getParameter("password");
        
        if("admin".equals(userName) && "123".equals(password)) {
            // response.getWriter().write("登录成功");
            response.setStatus(302);
            response.setHeader("Location", "login_success.html");
        }else {
            response.getWriter().write("登录失败");
        }
        
    }

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

}

效果

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<h1>登录成功!!!</h1>
</body>
</html>

效果

重定向

package com.dashucoding.servlet;

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

/**
 * Servlet implementation class LoginServlet
 */
public class LoginServlet extends HttpServlet {
    
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        // public void setContextType(String type)
        // 设置将发送到客户端的响应的内容类型,如果该响应尚未提交,给定内容类型可能包含字符编码规范,例如
        // text/html;charseet=UTF-8,如果在调用 getWriter之前调用此方法,则只根据给定内容类型设置响应的字符编码
        
        response.setContentType("text/html;charset=utf-8");
        
        String userName = request.getParameter("username");
        String password = request.getParameter("password");
        
        if("admin".equals(userName) && "123".equals(password)) {
            // response.getWriter().write("登录成功");
            /*response.setStatus(302);
            response.setHeader("Location", "login_success.html");*/
            
            // 重定向写法,重新定位方向
            // response.sendRedirect("login_success.html");
            
            // 请求转发的写法
            request.getRequestDispatcher("login_success.html").forward(request, response);
            
        }else {
            response.getWriter().write("登录失败");
        }
        
    }

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

}

`Cookie`

用于自动登录,浏览记录等,是服务器给客户端的.

Cookie cookie = new Cookie("a","b");
// 响应
response.addCookie(cookie);

获取Cookie

package com.dashucoding.servlet;

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;

/**
 * Servlet implementation class Demo01
 */
public class Demo01 extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
        //Cookie的简单使用。
        
        //cookie 发送给客户端，并且保存在客户端上的一份小数据
        
        response.setContentType("text/html;charset=utf-8");
        
        //发送cookie给客户端
        Cookie cookie = new Cookie("aa", "bb");
        //给响应，添加一个cookie
        response.addCookie(cookie);
        response.getWriter().write("请求成功了...");
        
        
        
        //获取客户端带过来的cookie
        Cookie[] cookies = request.getCookies();
        if(cookies != null){
            for (Cookie c : cookies) {
                String cookieName = c.getName();
                String cookieValue = c.getValue();
                System.out.println(cookieName + " = "+ cookieValue);
            }
        }
        
    }

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


}

Cookie是一份小数据,是服务器给客户端,存储在客户端上的一份小数据.

http请求是无状态的.

在响应的时候添加Cookie

Cookie cookie = new Cookie("name", "value");
// 添加cookie
response.addCookie(cookie);

在客户端信息里,响应头中多了Set-Cookie

获取客户端带来的Cookie

Cookie[] cookies = request.getCookies();
if(cookies != null){
 for(Cookie c : cookies){
  String cookieName = c.getName();
  String cookieValue = c.getValue();
  System.out.println(cookieName + " = " + cookieValue);
 }
}

cookie过期

public int getMaxAge() 返回以秒为单位指定的cookie的最大生存时间.

public void setMaxAge(int expiry) 设置cookie的最大生存时间,以秒为单位.

如何显示上次登录时间

可以进行判断账号密码,如果上次有登录过,那么显示上次的登录时间.这里分两种情况,获取带过来的cookie进行判断,第一种是没有cookie的,第一次登录,输出登录成功或者失败,然后给客户端添加cookie,new Cookie(),第二种的登录过的,还是要输出登录成功或者是失败,获取以前的cookie.时间戳要重置怎么理解?

package com.dashucoding.servlet;

import java.io.IOException;
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;

import com.dashucoding.util.CookieUtil;

/**
 * Servlet implementation class Demo03
 */
public class Demo03 extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
        response.setContentType("text/html;charset=utf-8");
        
        String userName = request.getParameter("username");
        String password = request.getParameter("password");
        
        if("admin".equals(userName) && "123".equals(password)){
            //获取cookie last-name --- >
            Cookie [] cookies = request.getCookies();
            
            //从数组里面找出我们想要的cookie
            Cookie cookie = CookieUtil.findCookie(cookies, "last");
            
            //是第一次登录，没有cookie
            if(cookie == null){
                
                Cookie c = new Cookie("last", System.currentTimeMillis()+"");
                c.setMaxAge(60*60); //一个小时
                response.addCookie(c);
                
                response.getWriter().write("欢迎您, "+userName);
                
            }else{
                //1. 去以前的cookie第二次登录，有cookie
                long lastVisitTime = Long.parseLong(cookie.getValue());
                
                //2. 输出到界面，
                response.getWriter().write("欢迎您, "+userName +",上次来访时间是："+new Date(lastVisitTime));
                
                
                //3. 重置登录的时间
                cookie.setValue(System.currentTimeMillis()+"");
                response.addCookie(cookie);
            }
        }else{
            response.getWriter().write("登陆失败 ");
        }
    
    }

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

如何显示商品浏览记录

获取提交过来的id,把id放入到cookie里,跳转界面.

servlet?id=1;
servlet?id=2;
获取cookie 1
1#2
setValue("1#2");

jsp

效果

效果

// index.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
 <br>---------1------------<br>
 <%! int a = 123; %>
 <br>---------2------------<br>
 <% int b = 123456; %>
 <br>---------3------------<br>
 <%=a %><br>
 <%=b %>
</body>
</html>

浏览记录

package com.dashucoding.util;

import javax.servlet.http.Cookie;

public class CookieUtil {
    /**
     * 从一个cookie数组中找到具体我们想要的cookie对象
     * @param cookies
     * @param name
     * @return
     */
    public static Cookie findCookie(Cookie[] cookies , String name){
        if(cookies != null){
            for (Cookie cookie : cookies) {
                if(name.equals(cookie.getName())){
                    return cookie;
                }
            }
        }
        return null;
    }
}

                <!-- 显示浏览记录 -->
                <%
                Cookie[] cookies = request.getCookies();
                Cookie cookie = CookieUtil.findCookie(cookies, "history");
                 // 如果cookie是空,表明没有浏览商品
                 if(cookie == null){
                %>
                 <h2> 您还没有浏览任何商品! </h2>
                <%
                }else{
                    // 不是空,表明有浏览记录
                    String[] ids = cookie.getValue().split("#");
                    for(String id : ids){
                %>
                <li style="width: 150px;height: 216;text-align: center;"><img src="products/1/cs1000<%=id %>.jpg" width="130px" height="130px" /></li>
                <%
                    }
                }
                %>

package com.dashucoding.servlet;

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;

import com.dashucoding.util.CookieUtil;

public class ProductInfoServlet extends HttpServlet {
    
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String id = request.getParameter("id");
        Cookie[] cookies = request.getCookies();
        Cookie cookie = CookieUtil.findCookie(cookies, "history");
        if (cookie==null) {
            Cookie cook = new Cookie("history", id);
            cook.setMaxAge(60*60*24*7);
            response.addCookie(cook);
        }else{
            String id2 = cookie.getValue();
            cookie.setValue(id+"#"+id2);
            cookie.setMaxAge(60*60*24*7);
            response.addCookie(cookie);
        }
        response.sendRedirect("product_info.htm");
    }


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

清除浏览记录

清除cookie

package com.dashucoding.servlet;

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;

/**
 * Servlet implementation class ClearHistory
 */
public class ClearHistory extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        // 清除cookie
        Cookie c = new Cookie("history", "");
        c.setMaxAge(0);
//      c.setPath("/demo1");
        response.addCookie(c);
        response.sendRedirect("product_list.jsp");
    }

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

}

获取cookie,添加cookie

request.getCookie();
response.addCookie();

Cookie分类

cookie.setMaxAge(0); // 删除
cookie.setMaxAge(100); // 100秒

Cloneable

创建一个cookie,cookie是servlet发送到web浏览器中的少量信息,这些信息是由浏览器保存,然后发送回到服务器中.

cookie的值是唯一标识客户端的,可以用于cookie会话管理.一个cookie拥有一个名,值,可以有一些可选属性.但又cookie也存在一些问题.浏览器支持每个web服务器又20个cookie,共有300个cookie,每个限制在4KB.

安全隐患,大小与个数限制.

`Session`

会话,Session是基于Cookie的一种会话机制.Cookie是服务器返回一部分小数据在客户端,存放在客户端上.

Session是把数据存放在服务端.

interface httpsession

public interface httpSession

常用的方法

package com.dashucoding.servlet;

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

/**
 * Servlet implementation class Demo01
 */
public class Demo01 extends HttpServlet {
    
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        HttpSession session = request.getSession();
        // 得到会话ID
        session.getId();
        // 存值
        session.setAttribute(name, value);
        // 取值
        session.getAttribute(name);
        // 移植
        session.removeAttribute(name);
    }

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

}

效果

效果

// web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>SessionDemo02</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <description></description>
    <display-name>LoginServlet</display-name>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>com.dashucoding.servlet.LoginServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/login</url-pattern>
  </servlet-mapping>
</web-app>

// LoginServlet
package com.dashucoding.servlet;

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

/**
 * Servlet implementation class LoginServlet
 */
public class LoginServlet extends HttpServlet {
    
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().write("收到请求了");
    }

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

}

// login.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
    <form action="login">
        账号: <input type="text"  name="username"/><br>
        密码: <input type="text"  name="password"/><br>
        <input type="submit"  value="登录"/><br>
    </form>
</body>
</html>

session创建与销毁

创建 request.getSession();
销毁 Redis session 存放在服务器内存中的数据
session关闭服务器销毁
session会话时间过期

// 可以改的 conf\web.xml 有效期30分钟
<session-config>
 <session-timeout>30</session-timeout>
</session-config>

package com.dashucoding.servlet;

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

/**
 * Servlet implementation class LoginServlet
 */
public class LoginServlet extends HttpServlet {
    
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        
        response.setContentType("text/html;charset=utf-8");
        
        String sessionid = request.getSession().getId();
        System.out.println("sessionid="+sessionid);
        // cookid id -> sessionid
        response.getWriter().write("收到请求了");
    }

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

}

session分析

商品列表添加商品,点击商品添加到购物车,到servlet.

获取点击商品标识id,存储到购物车,跳转界面.

判断购物车是否有商品,有数量加1,没有数量等于1.

购物车

效果

效果

效果

package com.dashucoding.servlet;

import java.io.IOException;
import java.util.LinkedHashMap;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class CarServlet
 */
public class CarServlet extends HttpServlet {
    
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        
        response.setContentType("text/html;charset=utf-8");
        // 获取添加到购物车的商品id
        int id = Integer.parseInt(request.getParameter("id"));
        // cat dog big pig
        String [] names = {"cat","dog","big","pig"};
        // 取到id对应商品
        
        String name = names[id];
        
        // 获取购物车存放东西的session
        // 把一个map 对象存放到session里面去,保证只有一次
        
        Map<String, Integer> map = (Map<String, Integer>) request.getSession().getAttribute("cat");
        
        if(map == null) {
            // value -> map
            
            map = new LinkedHashMap<String, Integer>();
            
            request.getSession().setAttribute("cat", map);
        }
        
        // 判断购物车里有没有该商品
        if(map.containsKey(name)) {
            // 在原来基础上 +1
            map.put(name, map.get(name)+1);
        }else {
            map.put(name, 1);
        }
        
        response.getWriter().write("<a href='product_list.jsp'><h2>继续购物</h2></a>");
        response.getWriter().write("<a href='cart.jsp'><h2>去购物车结算</h2></a>");
    }


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

}

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
 <a href="CarServlet?id=0"><h2>cat</h2></a><br>
 <a href="CarServlet?id=1"><h2>dog</h2></a><br>
 <a href="CarServlet?id=2"><h2>big</h2></a><br>
 <a href="CarServlet?id=3"><h2>pig</h2></a><br>
</body>
</html>

效果

效果

// cart.jsp
<%@page import="java.util.Map"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
 您的购物车商品如下:
 <%
  // 获取到map
  Map<String,Integer> map = (Map<String,Integer>)session.getAttribute("cat");
  // 遍历
  if(map != null){
      for(String key : map.keySet()){
          int value = map.get(key);
          // key:商品名称 value:商品名称
          // <h3>名称： 数量: </h3>
  %>
        <h3>名称: <%=key %> 数量: <%=value %></h3><br>
  <%
      }
  }
  %>
</body>
</html>

效果

package com.dashucoding.servlet;

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

/**
 * Servlet implementation class ClearCartServlet
 */
public class ClearCartServlet extends HttpServlet {
    
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        
        HttpSession session = request.getSession();
        
        // cat购物车
        session.removeAttribute("cat");
        response.sendRedirect("cart.jsp");
        
    }

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

}

<%@page import="java.util.Map"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
 您的购物车商品如下:
 <%
  // 获取到map
  Map<String,Integer> map = (Map<String,Integer>)session.getAttribute("cat");
  // 遍历
  if(map != null){
      for(String key : map.keySet()){
          int value = map.get(key);
          // key:商品名称 value:商品名称
          // <h3>名称： 数量: </h3>
  %>
        <h3>名称: <%=key %> 数量: <%=value %></h3><br>
  <%
      }
  }
  %>
  <a href="ClearCartServlet"><h4>清空购物车</h4></a>
</body>
</html>

效果

public void invalidate()
使用,会话无效,取消对任何绑定到它的对象.
// 强制干掉会话
// session.invalidate();

小结

cookie和session

Cookie 获取上一次访问时间,获取浏览记录,数据存放在客户端

Session 会话技术,数据存放在服务端

setAttribute 存放数据
getAttribute 取数据
removeAttribute 移除
getSessionId() 获取会话id
invalidate() 让会话失效

response.addCookie(new Cookie())
request.getSession 创建

如果看了觉得不错

点赞！转发！

达叔小生：往后余生，唯独有你 You and me, we are family ! 90后帅气小伙，良好的开发习惯；独立思考的能力；主动并且善于沟通简书博客：达叔小生 https://www.jianshu.com/u/c785ece603d1

结语

下面我将继续对其他知识深入讲解，有兴趣可以继续关注
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原始发表：2019.01.23 ，如有侵权请联系 cloudcommunity@tencent.com 删除

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