第74节：Java中的Cookie和Session

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第74节：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：

// 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);
		}
	}
}

登录

// 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>

// 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);
	}

}

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

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

// 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=" 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);
	}

}

// 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 confweb.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

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>

// 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>

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>

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
小礼物走一走 or 点赞

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原文地址：https://www.cnblogs.com/dashucoding/p/10312527.html

第74节：Java中的Cookie和Session

ServletContext:

HttpServletRequest:

HttpServletResponse:

Cookie

Session

小结

结语

`ServletContext`:

`HttpServletRequest`:

`HttpServletResponse`:

`Cookie`

`Session`