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