Servlet的四大作用域：Page，Request，Session，Application。主要是用来存放共享数据！
一、 Page作用域对应的作用域访问对象为pageContext对象。
作用范围：当前整个jsp页面。
生命周期：当对JSP的请求时开始，当响应结束时销毁。
package com.ape.view;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet("/Demo1Servlet")
public class Demo1Servlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//处理乱码
request.setCharacterEncoding("utf-8");
response.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
//获取资源
PrintWriter out = response.getWriter();
out.print("页面1");
// page域(当前页面使用)
String name1="张无忌";
out.print(name1);
out.close();
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
输出结果为：
当我们在页面2输出name1时，发现直接报错输出不了的，证明只在当前页面起作用。
二、Request作用域
对应的作用域访问对象为request对象。
作用范围：request表示一个请求，只要发出一个请求就会创建一个request，它作用于整个请求链（转发并不会终止此请求链）。
生命周期：当浏览器发送请求到后台时创建，当请求结束，request被销毁。
package com.ape.view;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet("/Demo1Servlet")
public class Demo1Servlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//处理乱码
request.setCharacterEncoding("utf-8");
response.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
//获取资源
PrintWriter out = response.getWriter();
out.print("页面1");
//request域(在同一个请求中使用，需要转发)
String name2="周芷若";
request.setAttribute("name2", name2);
out.print(request.getAttribute("name2"));
//转发
// request.getRequestDispatcher("Demo2Servlet").forward(request, response);
out.close();
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
当不转发时，拿到的页面1和页面2的结果如下：
当做了转发后，地址栏并未改变，但是页面2就拿到了值：
三、Session作用域对应的作用域访问对象为session对象。
作用范围：在当前浏览器进行数据共享，一次会话。
生命周期：在浏览器启动时会创建，当浏览器关闭时被销毁，存在无操作默认销毁时间。
package com.ape.view;
import java.io.IOException;
import java.io.PrintWriter;
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;
@WebServlet("/Demo1Servlet")
public class Demo1Servlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//处理乱码
request.setCharacterEncoding("utf-8");
response.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
//获取资源
PrintWriter out = response.getWriter();
HttpSession session = request.getSession();
out.print("页面1");
//session域(在同一个会话中)
String name3="赵敏";
session.setAttribute("name3", name3);
out.print(session.getAttribute("name3"));
out.close();
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
package com.ape.view;
import java.io.IOException;
import java.io.PrintWriter;
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;
@WebServlet("/Demo2Servlet")
public class Demo2Servlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//处理乱码
request.setCharacterEncoding("utf-8");
response.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
//获取资源
PrintWriter out = response.getWriter();
HttpSession session = request.getSession();
out.print("页面2");
//session域(在同一个会话中)
out.print(session.getAttribute("name3"));
out.close();
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
输出结果为：
四、Application作用域
对应的作用域访问对象为application对象。
作用范围：整个web项目。
生命周期：在启动Web项目时创建，代表整个web项目，是其中最大的作用域，当服务关闭或时项目停止时被销毁。
package com.ape.view;
import java.io.IOException;
import java.io.PrintWriter;
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;
@WebServlet("/Demo1Servlet")
public class Demo1Servlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//处理乱码
request.setCharacterEncoding("utf-8");
response.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
//获取资源
PrintWriter out = response.getWriter();
ServletContext sc = getServletContext();
out.print("页面1");
//application域(整个应用中，服务器重启)
String name4="殷离";
sc.setAttribute("name4", name4);
out.print(sc.getAttribute("name4"));
out.close();
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
package com.ape.view;
import java.io.IOException;
import java.io.PrintWriter;
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;
@WebServlet("/Demo2Servlet")
public class Demo2Servlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//处理乱码
request.setCharacterEncoding("utf-8");
response.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
//获取资源
PrintWriter out = response.getWriter();
ServletContext sc = getServletContext();
out.print("页面2");
//application域(整个应用中，服务器重启)
out.print(sc.getAttribute("name4"));
out.close();
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
输出结果为：
四个作用域的区别：
Application > Session > Request > Page
小结：
