1.会话
会话:用户打开一个浏览器,点击很多超链接,访问很多个web资源,关闭浏览器,这个过程称之为会话。
有状态会话:一个同学来过,下次再来教室的时候,我们会知道这个同学,曾经来过,称之为有状态会话;
你能怎么证明你是中国人?
国家 你
1.有户籍 国家给你户籍
2.身份证 国家标记你身份
一个网站,怎么证明你来过?
客户端 服务端
1.服务端给客户端一个信件,客户端下次访问服务端带上信件就可以了;cookie
2.服务器登记你来过了,下次你来的时候我来匹配你;session
2.保存会话的两种技术
cookie:
客户端技术 (请求,响应)
session:
服务器技术,利用这个技术,可以保存会话信息?。我们可以把信息或者数据放在session中。
常见:网站登录之后,你下次不用再登录了,第二次访问直接就上去了。
cookie:
1.从请求中拿到cookie信息 2.服务端响应给客户端cookie
//cookie,服务器从客户端获取 Cookie[] cookies = req.getCookies();//这里返回数组,说 明cookie可能存在多个 cookie.getName();//获取cookie中key cookie.getValue();//获取cookie中的是vlaue Cookie cookie = new Cookie("lastLoginTime",System.currentTimeMillis()+"");新建一个cookie resp.addCookie(cookie);//给客户端响应一个cookie
cookie:一般会保存在本地的用户目录下appdata
问题:一个网站cookie是否存在上限!细节!:
一个cookie只能保存一个信息
一个web站点可以给浏览器发送多个cookie,最多存放20个cookie;
cookie大小有限制4kb
300个cookie浏览器上限
删除cookie:
不设置有效期,关闭浏览器,自动失效。
设置有效期为0;
实现代码如下:
//CookieDemo01 package com.kuang.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; //保存用户上一次访问的时间 public class CookieDemo01 extends HttpServlet { @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req,resp); } @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //服务器,告诉你,你来的时间,把这个时间封装成一个信件,你带来,我就知道你来了了 //解决中文乱码 req.setCharacterEncoding("utf-8"); resp.setCharacterEncoding("utf-8"); resp.setContentType("text/html;charset=utf-8"); System.out.println("sjfskahfs"); PrintWriter out = resp.getWriter(); //cookie,服务器从客户端获取 Cookie[] cookies = req.getCookies();//这里返回数组,说明cookie可能存在多个 //判断cookie是否存在 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]; //获取cookie的名字 if( cookie.getName().equals("lastLoginTime")){ // 获取cookie中的值 long lastLoginTime = Long.parseLong(cookie.getValue()); Date date = new Date(lastLoginTime); out.write(date.toLocaleString()); } } }else { out.write("这是您第一次访问本站"); } //服务给客户端响应一个cookie Cookie cookie = new Cookie("lastLoginTime",System.currentTimeMillis()+""); resp.addCookie(cookie); } } //CookieDemo02 package com.kuang.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 CookieDemo02 extends HttpServlet { @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req,resp); } @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //创建一个cookie,名字必须要和删除的名字一致。 Cookie cookie = new Cookie("lastLoginTime",System.currentTimeMillis()+""); cookie.setMaxAge(0);//将cookie有效期设置为零 resp.addCookie(cookie); } } //web.xml <!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd" > <web-app> <display-name>Archetype Created Web Application</display-name> <servlet> <servlet-name>CookieDemo01</servlet-name> <servlet-class>com.kuang.servlet.CookieDemo01</servlet-class> </servlet> <servlet-mapping> <servlet-name>CookieDemo01</servlet-name> <url-pattern>/c</url-pattern> </servlet-mapping> <servlet> <servlet-name>CookieDemo02</servlet-name> <servlet-class>com.kuang.servlet.CookieDemo02</servlet-class> </servlet> <servlet-mapping> <servlet-name>CookieDemo02</servlet-name> <url-pattern>/c2</url-pattern> </servlet-mapping> </web-app>
session
什么是session:
服务器会给每个用户(浏览器)创建一个session对象;
一个session独占一个浏览器,只要浏览器没有关闭,这个session就存在
用户登录后,整个网站它都可以访问!
列:保存用户的信息;
保存购物车的信息;
session和cookie的区别:
cookie是把用户的数据写给用户的浏览器,浏览器保存,可以保存多个
session把用户的数据保存到用户独占的session中,服务端保存,保存重要的信息,减少服务器资源浪费
session对象由服务创建
使用场景:
保存一个登陆用户的信息
购物车信息
在整个网站中经常会使用的数据,将他保存到session中
附上代码:
//Person package com.kuang.pojo; public class Person { private String name; private int age; public Person(String name,int age) { this.name = name; this.age = age; } @Override public String toString() { return "Person{" + "name='" + name + '\'' + ", age=" + age + '}'; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } } //SessionDemo01 package com.kuang.servlet; import com.kuang.pojo.Person; import javax.servlet.ServletException; import javax.servlet.http.*; import java.io.IOException; public class SessionDemo01 extends HttpServlet { @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { super.doPost(req, resp); } @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //解决乱码问题 resp.setContentType("text/html;charset=utf-8"); resp.setCharacterEncoding("UTF-8"); req.setCharacterEncoding("UTF-8"); //得到session HttpSession session = req.getSession(); //给session中存东西 Person person = new Person("耶耶耶",20); session.setAttribute("name",person); //获取sessionID String sessionId = session.getId(); //判断session是不是新建 if (session.isNew()){ resp.getWriter().write("session创建成功,ID:"+ sessionId); }else { System.out.println(session.getAttribute("name"));//获取session值 resp.getWriter().write("session以及在服务器中存在了,ID:"+sessionId); } //session创建的时候做了什么事情 //Cookie cookie = new Cookie("JSESSIONID",sessionId); //resp.addCookie(cookie); } } //SessionDemo02 package com.kuang.servlet; import com.kuang.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 SessionDemo02 extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //解决乱码问题 req.setCharacterEncoding("UTF-8"); resp.setCharacterEncoding("UTF-8"); resp.setContentType("text/html;charset=utf-8"); //得到session 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); } } //SessionDemo03 package com.kuang.servlet; 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 SessionDemo03 extends HttpServlet { @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req,resp); } @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { HttpSession session = req.getSession(); session.removeAttribute("name");//注销session } } //web.xml <!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd" > <web-app> <display-name>Archetype Created Web Application</display-name> <servlet> <servlet-name>CookieDemo01</servlet-name> <servlet-class>com.kuang.servlet.CookieDemo01</servlet-class> </servlet> <servlet-mapping> <servlet-name>CookieDemo01</servlet-name> <url-pattern>/c</url-pattern> </servlet-mapping> <servlet> <servlet-name>CookieDemo02</servlet-name> <servlet-class>com.kuang.servlet.CookieDemo02</servlet-class> </servlet> <servlet-mapping> <servlet-name>CookieDemo02</servlet-name> <url-pattern>/c2</url-pattern> </servlet-mapping> <servlet> <servlet-name>SessionDemo01</servlet-name> <servlet-class>com.kuang.servlet.SessionDemo01</servlet-class> </servlet> <servlet-mapping> <servlet-name>SessionDemo01</servlet-name> <url-pattern>/s1</url-pattern> </servlet-mapping> <servlet> <servlet-name>SessionDemo02</servlet-name> <servlet-class>com.kuang.servlet.SessionDemo02</servlet-class> </servlet> <servlet-mapping> <servlet-name>SessionDemo02</servlet-name> <url-pattern>/s2</url-pattern> </servlet-mapping> <servlet> <servlet-name>SessionDemo03</servlet-name> <servlet-class>com.kuang.servlet.SessionDemo03</servlet-class> </servlet> <servlet-mapping> <servlet-name>SessionDemo03</servlet-name> <url-pattern>/s3</url-pattern> </servlet-mapping> <!--设置session默认值的失效时间--> <session-config> <!--1分钟后session自动失效,以分钟为单位--> <session-timeout>1</session-timeout> </session-config> </web-app>
servletcontext作用域比session与cookie大,session与cookie都是针对个人的,但servletcontext是所有人共享的。