前言：
本文内容：Cookie讲解、Session讲解
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Cookie讲解
会话
用户打开浏览器，点击多个超链接，访问多个web资源，到关闭浏览器的整个过程称为会话；
有状态会话
每个用户有自己特有的一个实例，在用户的生存期内，bean保持了用户的信息，即“有状态”；一旦用户灭亡（调用结束或实例结束），bean的生命期也告结束。
保存会话的两种技术
Cookie
Session
Cookie
- 从请求中拿到cookie信息
- 服务器响应给客户端的cookie
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| Cookie[] cookies = req.getCookies();
cookie.getName();
cookie.getValue();
new Cookie("lastLoginTime",System.currentTimeMillis()+"");
cookie.setMaxAge(24*60*60);
resp.addCookie(cookie);
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Cookie小拓展：
- 一个Cookie只能存在一个信息
- 一个站点可以给浏览器发送多个cookie，最多存放20个cookie
- cookie大小限制4kb
- 300个cookie浏览器上限制
删除Cookie
- 不设置有效期，关闭浏览器后自动失效
- 设置有效时间为0
编码解码：
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URLEncoder.encode("张三","utf-8");
URLDecoder.decode(cookie,getValue(),"utf-8")
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Cookie练习：
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| package com.jokerdig.servlet;
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 java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;
public class CookieDemo1 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.setCharacterEncoding("utf-8");
resp.setContentType("text/html;charset=utf-8");
PrintWriter out = resp.getWriter();
Cookie[] cookies = req.getCookies();
if(cookies!=null){
out.write("你上一次访问的时间是：");
for (int i = 0; i < cookies.length; i++) {
Cookie cookie = cookies[i];
if(cookie.getName().equals("lastLoginTime")){
long lastLoginTime = Long.parseLong(cookie.getValue());
Date date = new Date(lastLoginTime);
out.write(date.toLocaleString());
}
}
}else{
out.write("这是第一次访问网站");
}
Cookie cookie = new Cookie("lastLoginTime", System.currentTimeMillis()+"");
cookie.setMaxAge(24*60*60);
resp.addCookie(cookie);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
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Session讲解
Session
服务器为了保存用户状态而创建的一个特殊的对象。(例如登录信息，购物车信息等)
当浏览器第一次访问服务器时，服务器创建一个session对象(该 对象有一个唯一的id,一般称之为sessionId),服务器会将sessionId 以cookie的方式发送给浏览器。
当浏览器再次访问服务器时，会将sessionId发送过来，服务器依据 sessionId就可以找到对应的session对象。
Session和Cookie的区别
- Cookie把用户的数据写给用户的浏览器，浏览器保存(可保存多个)
- Session把用户的数据写到用户独占Session中，服务器端保存(保存重要信息，减少服务器资源浪费)
- Session对象由服务创建
Session使用场景
- 保存用户登录信息
- 购物车信息
- 将整个网站中经常使用的数据放入session
Session练习
发送Session
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| package com.jokerdig.servlet;
import com.jokerdig.pojo.Person;
import javax.servlet.ServletException;
import javax.servlet.http.*;
import java.io.IOException;
import java.io.PrintWriter;
public class SessionDemo1 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.setCharacterEncoding("utf-8");
resp.setContentType("text/html;charset=utf-8");
HttpSession session = req.getSession();
session.setAttribute("name",new Person("李四",20));
String sessionid = session.getId();
if (session.isNew()){
resp.getWriter().write("session创建成功,sessionID："+sessionid);
}else{
resp.getWriter().write("session已经被创建,sessionID："+sessionid);
}
Cookie cookie = new Cookie("JSESSIONID", sessionid);
resp.addCookie(cookie);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
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接收Session
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| package com.jokerdig.servlet;
import com.jokerdig.pojo.Person;
import javax.servlet.ServletException;
import javax.servlet.http.*;
import java.io.IOException;
public class SessionDemo2 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.setCharacterEncoding("utf-8");
resp.setContentType("text/html;charset=utf-8");
HttpSession session = req.getSession();
Person person = (Person) session.getAttribute("name");
System.out.println(person.toString());
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
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手动注销Session
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| package com.jokerdig.servlet;
import com.jokerdig.pojo.Person;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
public class SessionDemo3 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.setCharacterEncoding("utf-8");
resp.setContentType("text/html;charset=utf-8");
HttpSession session = req.getSession();
session.removeAttribute("name");
session.invalidate();
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
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Web.xml配置
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| <?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
version="4.0"
metadata-complete="true">
<servlet>
<servlet-name>cookie</servlet-name>
<servlet-class>com.jokerdig.servlet.CookieDemo1</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>cookie</servlet-name>
<url-pattern>/cookie</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>session</servlet-name>
<servlet-class>com.jokerdig.servlet.SessionDemo1</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>session</servlet-name>
<url-pattern>/se</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>session2</servlet-name>
<servlet-class>com.jokerdig.servlet.SessionDemo2</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>session2</servlet-name>
<url-pattern>/se2</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>session3</servlet-name>
<servlet-class>com.jokerdig.servlet.SessionDemo3</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>session3</servlet-name>
<url-pattern>/se3</url-pattern>
</servlet-mapping>
<session-config>
<session-timeout>15</session-timeout>
</session-config>
</web-app>
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