servlet中request session servletContext 测试示例

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Java

Servlet ITeye Web XML

基本概念：.request session servletContext对象保持的数据范围区别
   1.request :保持的数据仅在下一个request中得到用在页面转发时共享数据
   2.session 作用域表示在一个用户与服务器会话范围之内直到客户端关闭或session超时
   3.servletContext中对象存取的数据是个全局的，生命周期也是长久的，直到web服务器关闭

示例：

package com.qingbyqing.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

//servlet中对象作用域 测试： ServletRequest  Session ServletContext  
public class SessionScopeTest extends HttpServlet {
	public void service(HttpServletRequest request, HttpServletResponse response)
			throws IOException {
		
		System.out.println("_______________________________");
		
		PrintWriter writer = response.getWriter();
		writer.println("<html> <head> </head> <body>");
		HttpSession session = request.getSession();
		ServletContext servletContext = this.getServletContext();

		Integer iRequest = (Integer) request.getAttribute("count");

		Integer iSession = (Integer) session.getAttribute("count");

		Integer iContext = (Integer) servletContext.getAttribute("count");

		if (iRequest == null) {
			iRequest = new Integer(1);
			request.setAttribute("count", iRequest);

		} else {

			System.out.println(iRequest.toString());
			int intValue = iRequest.intValue();
			intValue++;
			iRequest = new Integer(intValue);
			request.setAttribute("count", iRequest);
		}
		System.out.println("request:  " + (iRequest.intValue()));
		writer.println("</br> request:  " + (iRequest.intValue()));
		if (iSession == null) {

			iSession = new Integer(1);

			request.getSession().setAttribute("count", iSession);
		} else {

			int intValue = iSession.intValue();
			intValue++;
			iSession = new Integer(intValue);

			request.getSession().setAttribute("count", iSession);
		}

		System.out.println("Session:  " + (iSession.intValue()));

		writer.println("</br> Session:  " + (iSession.intValue()));

		if (iContext == null) {
			iContext = new Integer(1);

			this.getServletContext().setAttribute("count", iContext);

		} else {

			int intValue = iContext.intValue();
			intValue++;
			iContext = new Integer(intValue);

			this.getServletContext().setAttribute("count", iContext);
		}

		System.out.println("sevletContext:  " + (iContext.intValue()));

		writer.println("</br> sevletContext:  " + (iContext.intValue()));

		writer.println("</body></html>");
	}
}

在web.xml中的配置：

<servlet>
	<description>this is a session scope test</description>
      <display-name>this is a session scope test</display-name>
      
      <servlet-name>SessionScopeTest</servlet-name>	
	<servlet-class>com.qingbyqing.servlet.SessionScopeTest</servlet-class>
	
	</servlet>
	
<servlet-mapping>
	<servlet-name>SessionScopeTest</servlet-name>
	<url-pattern>/com.qingbyqing.servlet/SessionScopeTest</url-pattern>
	
	</servlet-mapping>

结果如下：
firfox中显示：