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社区首页 >专栏 >第74节：Java中的Cookie和Session

第74节：Java中的Cookie和Session

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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
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文章被收录于专栏：达达前端达达前端
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

代码语言：javascript
复制
// 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>
代码语言：javascript
复制
// 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

代码语言：javascript
复制
// 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);
    }

}
代码语言：javascript
复制
// 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

代码语言：javascript
复制
// 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);
    }

}
代码语言：javascript
复制
// 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>
代码语言：javascript
复制
// 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

代码语言：javascript
复制
// 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

代码语言：javascript
复制
<!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

代码语言：javascript
复制
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.

代码语言：javascript
复制
Cookie cookie = new Cookie("a","b");
// 响应
response.addCookie(cookie);

获取Cookie

代码语言：javascript
复制
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

代码语言：javascript
复制
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

代码语言：javascript
复制
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?

代码语言：javascript
复制
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.

代码语言：javascript
复制
servlet?id=1;
servlet?id=2;
获取cookie 1
1#2
setValue("1#2");

jsp

效果

效果

代码语言：javascript
复制
// 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

代码语言：javascript
复制
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;
    }
}
代码语言：javascript
复制
                <!-- 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>
                <%
                    }
                }
                %>
代码语言：javascript
复制
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

代码语言：javascript
复制
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

代码语言：javascript
复制
request.getCookie();
response.addCookie();

Cookie分类

代码语言：javascript
复制
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

代码语言：javascript
复制
public interface httpSession

常用的方法

代码语言：javascript
复制
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

代码语言：javascript
复制
// 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>
代码语言：javascript
复制
// 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);
    }

}
代码语言：javascript
复制
// 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

代码语言：javascript
复制
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
代码语言：javascript
复制
// 可以改的 conf\web.xml 有效期30分钟
<session-config>
 <session-timeout>30</session-timeout>
</session-config>
代码语言：javascript
复制
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

代码语言：javascript
复制
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);
    }

}
代码语言：javascript
复制
<%@ 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

代码语言：javascript
复制
// 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

代码语言：javascript
复制
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);
    }

}
代码语言：javascript
复制
<%@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

代码语言：javascript
复制
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

代码语言：javascript
复制
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

代码语言：javascript
复制
setAttribute 存放数据
getAttribute 取数据
removeAttribute 移除
getSessionId() 获取会话id
invalidate() 让会话失效
代码语言：javascript
复制
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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目录
  • ServletContext:
  • HttpServletRequest:
  • HttpServletResponse:
  • Cookie
  • Session
  • 小结
  • 结语
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