JSP之四大作用域（pageContext,request,session,application）

小灰灰 2024-04-01 09:46 78阅读 0赞

JSP的四大作用域的存储和获取数据的方式一样，差别在于取值的范围不同。

四大域各自作用范围为：

pageContext:当前JSP页面有效

request:请求有效

session:会话有效（关闭浏览器则失效）

application:整个Web应用有效（服务器关闭或者重启则失效）

**1、pageContext作用域**  
(pageContextScope:键值，设值：李四)

由于输出脚本中的a是字符类型，所以需要对pageContext.getAttribute进行强制类型转换String a = (String)来解决输出脚本a的报错

jsp代码：创建一个jsp页面，在body标签里面书写以下代码

<%
    	pageContext.setAttribute("pageContextScope", "李四");
    	String a = (String) pageContext.getAttribute("pageContextScope");
    %>

servlet完整代码：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    	pageEncoding="UTF-8"%>
    <!DOCTYPE html>
    <html>
    <head>
    <meta charset="UTF-8">
    <title>pageConext作用域</title>
    </head>
    <body>
    	<%
    	pageContext.setAttribute("pageContextScope", "李四");
    	String a = (String) pageContext.getAttribute("pageContextScope");
    	%>
    
    	<h2>
    		pageContextScope:<%=a%>
    	</h2>
    </body>
    </html>

输出结果：

![329880585f874cb8bdf24042310ef0da.png][]

**2、request作用域**

创建一个servlet(ScopeServlet.java),在servlet里存值

**转发操作（可以获取到值）**

getRequestDispatcher:转发到页面；

forward：传递reqest,response

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		req.setAttribute("requestScope","李二");
    		req.getRequestDispatcher("/jsp/object/scope.jsp").forward(req, resp);
    		
    	}

req.getRequestDispatcher("转发路径")，我的转发jsp页面位于：webapp下的jsp/object文件夹下的scope.jsp

![91cf7e95a43f4b6ea37d3b1113ca75ce.png][]

jsp页面代码：

<h4>request域</h4>
    <%
        String b = (String) request.getAttribute("requestScope");
    %>
    requestScope:<%=b%>

注：由于Servlet发生变化，需要重新部署项目；

由于request是在servlet上存值，所以需要在ScopeServlet上启动；

输出结果：

![e1ecdd31f8bc4adcaa9df37a8affe674.png][]

**重定向操作（获取不到值）**

Servlet代码：

req.setAttribute("requestScope","李二");
    resp.sendRedirect(req.getContextPath()+"/jsp/object/scope.jsp");

jsp代码：

<h4>request域</h4>
    <%
    	String b = (String) request.getAttribute("requestScope");
    %>
    requestScope:<%=b%>

输出结果：

![de5e6676c033475e95dc9ef00f731f46.png][]

注：观察两者的区别

转发操作：地址栏没有发生变化

重定向操作：地址栏发生变化

**3、session作用域**

servlet代码：

req.getSession().setAttribute("sessionScope", "李三");

jsp代码：

<h4>session域</h4>
    	<%
    	String c = (String)session.getAttribute("sessionScope");
    	%>
    	session:<%=c %>

输出结果：

![393c283a84f244bfbad8dcc4d0c5c89d.png][]

4、application作用域

servlet代码：

注：servlet这里的作用域不是application而是servletContextScope，因为application对应的servlet类型是javax.servlet.servletContext

req.getServletContext().setAttribute("servletContextScope", "李四");

jsp代码：

注：

<h4>application域</h4>
    	<%
    	String d = (String) application.getAttribute("servletContextScope");
    	%>
    	application:<%=d %>

输出结果：

![242a2ad230654b34b383055deb002af5.png][]

完整代码：

servlet：

package com.servlet;
    
    import java.io.IOException;
    
    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(name="ScopeServlet",value="/scopeServlet")
    public class ScopeServlet extends HttpServlet{
    
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		req.setAttribute("requestScope","李二");
    		//req.getRequestDispatcher("/jsp/object/scope.jsp").forward(req, resp);
            
            //转发
    		//req.getRequestDispatcher("/jsp/object/scope.jsp").include(req, resp);
    		
    		//重定向
    		resp.sendRedirect(req.getContextPath()+"/jsp/object/scope.jsp");
    		 
    		req.getSession().setAttribute("sessionScope", "李三");
    		
    		req.getServletContext().setAttribute("servletContextScope", "李四");
    	}
    
    	@Override
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		super.doPost(req, resp);
    	}
    	
    }

jsp代码：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    	pageEncoding="UTF-8"%>
    <!DOCTYPE html>
    <html>
    <head>
    <meta charset="UTF-8">
    <title>pageConext\request\session\application四大作用域对象</title>
    </head>
    <body>
    	<h4>pageContext域</h4>
    	<%
    	pageContext.setAttribute("pageContextScope", "李一");
    	String a = (String) pageContext.getAttribute("pageContextScope");
    	%> 
    	pageContextScope:<%=a%>
    
    	<h4>request域</h4>
    	<%
    	String b = (String) request.getAttribute("requestScope");
    	%>
    	requestScope:<%=b%>
    
    	<h4>session域</h4>
    	<%
    	String c = (String) session.getAttribute("sessionScope");
    	%>
    	session:<%=c%>
    	<h4>application域</h4>
    	<%
    	String d = (String) application.getAttribute("servletContextScope");
    	%>
    	application:<%=d %>
    </body>
    </html>

复制地址栏的地址，关闭所有开启的浏览器页面，重新打开浏览器，粘贴地址回车，你会发现，session域也取不到值

![ffc273a891f046db8d843e15712aa1b0.png][]

仅供参考，如有不足之处，敬请见谅。

[329880585f874cb8bdf24042310ef0da.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/fea92e89e2a14e49b923961499091009.png
[91cf7e95a43f4b6ea37d3b1113ca75ce.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/4728d7cc23ce445faea32cd30e47cfa2.png
[e1ecdd31f8bc4adcaa9df37a8affe674.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/006c6d69e93a4ac9a6465e665167dafc.png
[de5e6676c033475e95dc9ef00f731f46.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/87a3b5415e814c5287231b7e6e9f6fb4.png
[393c283a84f244bfbad8dcc4d0c5c89d.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/953b87fa3efc427d9f67410ebfb5fb3a.png
[242a2ad230654b34b383055deb002af5.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/316380657d934a6888d0213c4ad7defa.png
[ffc273a891f046db8d843e15712aa1b0.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/ce5c0e54925f411587d858dee1e99e51.png