一. 简介

• 会话:用户打开浏览器，访问web服务器的资源，会话建立，直到有一方断开连接，会话结束。在一次会话中可以包含多次请求和响应

• 会话跟踪:一种维护浏览器状态的方法，服务器需要识别多次请求是否来自于同一浏览器，以便在同一次会话的多次请求间共享数据

• HTTP协议是无状态的,每次浏览器向服务器请求时, 服务器都会将该请求视为新的请求, 因此我们需要回话跟踪技术来实现回话内数据共享

• 实现方式:

1. 客户端回话跟踪技术: Cookie

2. 服务端会话跟踪技术: Session

二. Cookie

Cookie: 客户端会话技术, 将数据保存的客户端, 以后每次请求都携带Cookie数据进行访问

Cookie的基本使用

发送Cookie

1. 创建Cookie对象, 设置数据

Cookie cookie = new Cookie("key","value");

2. 发送Cookie到客户端: 使用response对象

response.addCookie(cookie);

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@WebServlet("/aServlet")
public class AServlet extends HttpServlet {protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//发送cookie//创建cookieCookie cookie = new Cookie("username","guaiwu");//发送到客户端: 使用request对象response.addCookie(cookie);}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doGet(request, response);}
}

获取Cookie

1. 获取客户端携带的所有Cookie, 使用request对象

Cookie[] cookies = request.getCookies();Cookie[] cookies = request.getCookies();

2. 遍历数组,获取所有Cookie对象

3. 使用Cookie对象方法获取数据

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@WebServlet("/bServlet")
public class BServlet extends HttpServlet {protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//获取cookie//获取客户端携带的所有CookieCookie[] cookies = request.getCookies();//遍历数组for (Cookie cookie : cookies) {if(cookie.getName().equals("username")){//使用cookie方法获取数据String name = cookie.getName();String value = cookie.getValue();System.out.println(name+"="+value);}}}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doGet(request, response);}
}

先访问http://localhost:8080/cookieDemo1/aServlet再访问http://localhost:8080/cookieDemo1/bServlet

Cookie原理

Cookie的实现是基于HTTP协议的

响应头: set-cookie

请求头: cookie

Cookie使用细节

Cookie存活时间

默认情况下，Cookie 存储在浏览器内存中，当浏览器关闭，内存释放，则Cookie被销毁

setMaxAge(int seconds): 设置Cookie存活时间(单位:秒)

1. 正数:将 Cookie写入浏览器所在电脑的硬盘，持久化存储。到时间自动删除

2. 负数:默认值，Cookie在当前浏览器内存中，当浏览器关闭，则 Cookie被销毁

3. 零:删除对应 Cookie

Cookie存储中文

Cookie不能直接存储中文

如果要存储中文必须进行转码: URL编码

代码

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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.net.URLEncoder;@WebServlet("/aServlet")
public class AServlet extends HttpServlet {protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//发送cookie//创建cookie//Cookie cookie = new Cookie("username","guaiwu");String value = "怪物";//URL编码value = URLEncoder.encode(value, "utf-8");Cookie cookie = new Cookie("username",value);//发送到客户端: 使用request对象response.addCookie(cookie);}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doGet(request, response);}
}

javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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.net.URLDecoder;@WebServlet("/bServlet")
public class BServlet extends HttpServlet {protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//获取cookie//获取客户端携带的所有CookieCookie[] cookies = request.getCookies();//遍历数组for (Cookie cookie : cookies) {if(cookie.getName().equals("username")){//使用cookie方法获取数据String name = cookie.getName();String value = cookie.getValue();//URL解码value = URLDecoder.decode(value, "utf-8");System.out.println(name+"="+value);break;}}}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doGet(request, response);}
}

结果展示

三. Session

服务端会话跟踪技术:将数据保存到服务端

JavaEE 提供 HttpSession接口，来实现一次会话的多次请求间数据共享功能

Session的基本使用

获取Session对象

HttpSession session = request.getSession();

Session对象功能

• void setAttribute(String name, Object o): 存储数据到 session 域中

• Object getAttribute(String name): 根据 key，获取值

• void removeAttribute(String name): 根据 key，删除该键值对

代码

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;@WebServlet("/demo1")
public class SessionDemo1 extends HttpServlet {protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//获取Session对象HttpSession session = request.getSession();//将数据存到session域中session.setAttribute("username","guaiwu");}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doGet(request, response);}
}

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;@WebServlet("/demo2")
public class SessionDemo2 extends HttpServlet {protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//获取session对象HttpSession session = request.getSession();//调用方法,获取值Object username = session.getAttribute("username");//如果可以打印出guaiwu说明实现了在一次回话的多次请求数据共享System.out.println(username);}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {this.doGet(request, response);}
}

效果展示

Session原理

Session是基于Cookie实现的

http://localhost:8080/cookieDemo1/demo1

http://localhost:8080/cookieDemo1/demo2

Session使用细节

Session 钝化、活化:

服务器重启后，Session中的数据是否还在?

• 钝化:在服务器正常关闭后， Tomcat会自动将 Session数据写入硬盘的文件中

• 活化:再次启动服务器后，从文件中加载数据到Session中

Session销毁

1. 默认情况下,无操作,30分钟后自动销毁

在web.xml下设置

• 50

2. 调用Session对象的invalidate()方法

Cookie和Session的区别

• 存储位置: Cookie 是将数据存储在客户端，Session 将数据存储在服务端

• 安全性: Cookie 不安全，Session 安全

• 数据大小: Cookie 最大3KB，Session 无大小限制

• 存储时间: Cookie 可以长期存储，Session 默认30分钟

• 服务器性能: Cookie 不占服务器资源，Session 占用服务器资源