Java中的域对象

快来打我* 2023-09-24 14:46 33阅读 0赞

> 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 {
        @Override
        protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            // 向request域中添加数据
            List<String> 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 {
        @Override
        protected 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<String> list =(List<String>) 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 {
        @Override
        protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            // 向Session域中添加数据
            HttpSession session = req.getSession();
            List<String> 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 {
        @Override
        protected 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<String> list =(List<String>) 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 {
        @Override
        protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            // 向Application域中添加数据
            ServletContext application = req.getServletContext();
            List<String> 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 {
        @Override
        protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            ServletContext application = this.getServletContext();
            // 从application域中读取数据
            List<String> list =(List<String>) application.getAttribute("list");
            System.out.println(list);
            System.out.println(application.getAttribute("gender"));
            System.out.println(application.getAttribute("name"));
        }
    }