Cookie、Session
会话
**会话:**用户打开一个浏览器,点击了很多超链接,访问多个web资源,关闭浏览器,这个过程可以称为会话。
有状态会话:
一个网站,怎么证明你来过?
- 客户端 服务端
- 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即可;cookie
- 服务器登记你来过,下次你来的时候进行匹配;session
保存会话的两种技术
- cookie
- 客户端技术(响应,请求)(服务端传给客户端通过响应,客户端传给服务端通过请求)
- session
- 服务器技术,利用这个技术,可以保存用户的会话信息,可以把信息或者数据放在Session中!
常见场景:网站登录之后,你下次不用再登录,第二次直接登录上去
Cookie
- 从请求中拿到cookie
- 服务器响应给客户端cookie
Cookie[] cookies = req.getCookies(); //获取cookie,服务器端从客户端获取 req
cookie.getName() //获得cookie中的key
cookie.getValue() //获得cookie中的值 value
Cookie cookie = new Cookie("lastLoginTime", System.currentTimeMillis()+""); //新建一个cookie
cookie.setMaxAge(24*60*60); //cookie 有效期为一天 设置cookie的有效期
resp.addCookie(cookie); //响应给客户端 一个cookie
package com.kk.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.net.URLEncoder;
import java.util.Date;
//保存用户上一次访问的时间
public class CookieDemo01 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//服务器 告诉你 来的时间 把这个世界封装成功一个 信件 下次带来,就知道你来了
//解决中文乱码
req.setCharacterEncoding("UTF-8");
resp.setCharacterEncoding("UTF-8");
//服务器 向 客户端反馈的时候 需要用resp.getWriter();流向客户端 输出数据 (服务器中的数据响应给客户端 resp)
PrintWriter out = resp.getWriter();
//Cookie 服务器端从客户端获取 使用request从客户端中获取Cookie
//这里返回数组,说明cookie可能存在多个
Cookie[] cookies = req.getCookies();
//判断cookie是否存在
if (cookies!=null){
//如果存在
out.write("你上一次访问的时间是:");
for (int i = 0; i < cookies.length; i++) {
Cookie cookie = cookies[i]; //遍历数组 找到对应的值
//获取cookie的名字
if (cookie.getName().equals("lastLoginTime")){
//获取cookie中的值
long lastLoginTime = Long.parseLong(cookie.getValue()); //转化为long的长整型
Date date = new Date(lastLoginTime);
out.write(date.toLocaleString());
}
}
}else{
out.write("这是您第一次访问本站!");
}
//服务器给客户端响应一个cookie
Cookie cookie = new Cookie("lastLoginTime", System.currentTimeMillis()+"");
cookie.setMaxAge(24*60*60); //cookie 有效期为一天
resp.addCookie(cookie);//使用resp (服务器响应给客户端 resp)
}
}
<servlet>
<servlet-name>CookieDemo01</servlet-name>
<servlet-class>com.kk.servlet.CookieDemo01</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>CookieDemo01</servlet-name>
<url-pattern>/c1</url-pattern>
</servlet-mapping>
一个网站cookie是否存在上限!
- 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;
- 这是有效期时间为0.
package com.kk.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 CookieDemo02 extends HttpServlet {
@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()+"");
//将cookie 有效期设置为0 立马过期
cookie.setMaxAge(0);
resp.addCookie(cookie);
}
}
<servlet>
<servlet-name>CookieDemo02</servlet-name>
<servlet-class>com.kk.servlet.CookieDemo02</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>CookieDemo02</servlet-name>
<url-pattern>/c2</url-pattern>
</servlet-mapping>
中文数据传递:
package com.kk.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.net.URLEncoder;
import java.util.Date;
//中文数据传递
public class CookieDemo03 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.setCharacterEncoding("utf-8");
resp.setCharacterEncoding("utf-8");
PrintWriter out = resp.getWriter();
//Cookie 服务器端从客户端获取 req
Cookie[] cookies = req.getCookies(); //这里放回数组,说明cookie可能存在多个
//判断cookie是否存在
if (cookies!=null){
//如果存在
out.write("你上一次访问的时间是:");
// for (Cookie cookie : cookies) {
//
// }
for (int i = 0; i < cookies.length; i++) {
Cookie cookie = cookies[i];
//获取cookie的名字
if (cookie.getName().equals("name")){
System.out.println(cookie.getValue());
//解码
out.write(URLEncoder.encode(cookie.getValue(),"utf-8"));
}
}
}else{
out.write("这是您第一次访问本站!");
}
//服务器给客户端响应一个cookie
//编码
Cookie cookie = new Cookie("name", URLEncoder.encode("陈","utf-8"));
//使用resp (服务器响应给客户端 resp)
resp.addCookie(cookie);
}
}
<servlet>
<servlet-name>CookieDemo03</servlet-name>
<servlet-class>com.kk.servlet.CookieDemo03</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>CookieDemo03</servlet-name>
<url-pattern>/c3</url-pattern>
</servlet-mapping>
Session
什么是Session?
- 服务器会给每一个用户(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;
- 用户登陆之后,整个网站都可以访问(保存用户的信息等… …)
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是把用户的数据写到用户独占Session中,服务器端保存(保存重要的信息,减少服务器资源浪费)
- Session对象由服务器创建
使用场景:
- 保存一个登录用户的信息;
- 购物车信息;
- 在整个网站中经常会使用的数据,我们将它保存在Session中;
SessionDemo01
package com.kk.servlet;
import pojo.Person;
import javax.servlet.ServletException;
import javax.servlet.http.*;
import java.io.IOException;
public class SessionDemo01 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();
//给Session中存东西
session.setAttribute("name",new Person("陈",18));
//获取Session的ID
String sessionId = session.getId();
//判断Session是不是新创建的
if (session.isNew()){
resp.getWriter().write("Session创建成功!,ID:"+sessionId);
}else{
resp.getWriter().write("Session已经在服务器存在!,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.kk.servlet;
import 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());
}
}
SessionDemo03
package com.kk.servlet;
import 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 SessionDemo03 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
HttpSession session = req.getSession();
session.removeAttribute("name");
//手动注销Session
session.invalidate();//注销
}
}
Person
package pojo;
public class Person {
private String name;
private int age;
public Person() {
}
public Person(String name, int age) {
this.name = name;
this.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;
}
@Override
public String toString() {
return "Person{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}
xml
<servlet>
<servlet-name>SessionDemo01</servlet-name>
<servlet-class>com.kk.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.kk.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.kk.servlet.SessionDemo03</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>SessionDemo03</servlet-name>
<url-pattern>/s3</url-pattern>
</servlet-mapping>
<!--设置Session默认的失效时间-->
<session-config>
<!--15分钟后Session失效(以分钟为单位)-->
<session-timeout>15</session-timeout>
</session-config>