什么是域对象?   

那些能放数据并存储传递数据作为数据存放区域的对象

能够存储数据,获取数据,传递数据的对象

Servlet三大域对象

• Request域                HTTPServletRequest          一次请求/请求转发
• Session域                 HTTPSession                       一次会话(跨请求)
• Application域          ServletContext                    任意一次请求和会话(跨会话)

setAttribute(name,value); 设置修改数据
getAttribute(name);获得数据的方法
removeAttribute(name);移除数据的方法

JSP四大域对象

• Page域
• Request域
• Session域
• Application域

1.Request域

有范围  :  一次请求内有效,请求转发时数据可以传递,除此之外该域没有办法实现数据共享

生命周期  :  创建 每发生一次请求创建一个独立的请求域

使用service方法中或者请求转发有效

销毁 请求结束,已经向浏览器响应数据

测试代码

向request域中放入数据

package com.msb.testRequest;
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 java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
/*** @Author: Ma HaiYang* @Description: MircoMessage:Mark_7001*/
@WebServlet(urlPatterns = "/addToRequest.do")
public class Servlet1 extends HttpServlet {@Overrideprotected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 向request域中添加数据List x=new ArrayList<>();Collections.addAll(x, "a","b","c");req.setAttribute("list", x);req.setAttribute("gender","boy");req.setAttribute("gender","girl");req.setAttribute("name","晓明");// 请求转发req.getRequestDispatcher("/readFromRequest.do").forward(req,resp);// 重定向//resp.sendRedirect("readFromRequest.do");}
}

request域中读取数据

package com.msb.testRequest;
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 java.io.IOException;
import java.util.List;
/*** @Author: Ma HaiYang* @Description: MircoMessage:Mark_7001*/
@WebServlet(urlPatterns="/readFromRequest.do")
public class Servlet2 extends HttpServlet {@Overrideprotected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 移除域中的互数据req.removeAttribute("gender");// 从request域中读取数据List list =(List) req.getAttribute("list");System.out.println(list);System.out.println(req.getAttribute("gender"));System.out.println(req.getAttribute("name"));//获取Request中的请求参数System.out.println(req.getParameter("username"));System.out.println(req.getParameter("password"));}
}

2.Session域

有效范围 : 单次会话内有效,可以跨多个请求

生命周期 :   创建 会话的产生,第一次发生请求,会话的开始

使用 本次会话之内,浏览器和服务器之间发生多次请求和响应有效

销毁 会话结束,如:浏览器失去JSESSIONID、到达最大不活动时间、手动清除

测试代码

Session域中放入数据

package com.msb.testSession;
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;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
/*** @Author: Ma HaiYang* @Description: MircoMessage:Mark_7001*/
@WebServlet(urlPatterns = "/addToSession.do")
public class Servlet1 extends HttpServlet {@Overrideprotected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 向Session域中添加数据HttpSession session = req.getSession();List x=new ArrayList<>();Collections.addAll(x, "a","b","c");session.setAttribute("list", x);session.setAttribute("gender","boy");session.setAttribute("gender","girl");session.setAttribute("name","晓明");// 重定向resp.sendRedirect("readFromSession.do");}
}

从Session域中读取数据

package com.msb.testSession;
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;
import java.util.List;
/*** @Author: Ma HaiYang* @Description: MircoMessage:Mark_7001*/
@WebServlet(urlPatterns="/readFromSession.do")
public class Servlet2 extends HttpServlet {@Overrideprotected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {HttpSession session = req.getSession();// 移除域中的互数据//session.removeAttribute("gender");// 从request域中读取数据List list =(List) session.getAttribute("list");System.out.println(list);System.out.println(session.getAttribute("gender"));System.out.println(session.getAttribute("name"));//获取Request中的请求参数System.out.println(req.getParameter("username"));System.out.println(req.getParameter("password"));}
}

3.Application域

有效范围 :  当前web服务内,跨请求,跨会话

生命周期 : 创建 项目启动 ,使用 项目运行任何时间有效

销毁 项目关闭

测试代码

Application域中放入数据

import javax.servlet.ServletContext;
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;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
/*** @Author: Ma HaiYang* @Description: MircoMessage:Mark_7001*/
@WebServlet(urlPatterns = "/addToApplication.do")
public class Servlet1 extends HttpServlet {@Overrideprotected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 向Application域中添加数据ServletContext application = req.getServletContext();List x=new ArrayList<>();Collections.addAll(x, "a","b","c");application.setAttribute("list", x);application.setAttribute("gender","girl");application.setAttribute("name","晓明");}
}

Application域中读取数据

package com.msb.testApplication;
import javax.servlet.ServletContext;
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;
import java.util.List;
/*** @Author: Ma HaiYang* @Description: MircoMessage:Mark_7001*/
@WebServlet(urlPatterns="/readFromApplication.do")
public class Servlet2 extends HttpServlet {@Overrideprotected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {ServletContext application = this.getServletContext();// 从application域中读取数据List list =(List) application.getAttribute("list");System.out.println(list);System.out.println(application.getAttribute("gender"));System.out.println(application.getAttribute("name"));}
}