两个Servlet 一个用于初始化转发 一个用于显示 以下为第一个

package com.test;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class Tip extends HttpServlet {

    /**
     * @author Administrator
     */    private static final long serialVersionUID = 1L;

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        request.setAttribute("request", "Request");

        HttpSession session = request.getSession();
        // 秒为单位，单个session的生存时长设置，
        // 优先级高于Web.xml的全局设置，默认为TomCat服务器的30min,其他服务器略有不同
        session.setMaxInactiveInterval(300);
        session.setAttribute("session", "Session");

        ServletContext servletContext = getServletContext();
        servletContext.setAttribute("context", "Context");

        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        out.println("Tip1已运行");

        request.getRequestDispatcher("tip2").forward(request, response);
    }
}

第二个显示Servlet

package com.test;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class Tip2 extends HttpServlet {

    /**
     * @author Administrator
     */    private static final long serialVersionUID = 1L;

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String rv = (String) request.getAttribute("request");
        HttpSession session = request.getSession();

        String sv = (String) session.getAttribute("session");
        ServletContext servletContext = getServletContext();
        String cv = (String) servletContext.getAttribute("context");

        System.out.println("Request值为" + rv);
        System.out.println("Session值为" + sv);
        System.out.println("Context值为" + cv);
        System.out.println("----分界线----");

        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        out.println("Tip2已运行");
        out.flush();
    }

}

XML文档

 <servlet>
 <servlet-name>Tip</servlet-name>
 <servlet-class>com.test.Tip</servlet-class>
 </servlet>
 
 <servlet-mapping>
 <servlet-name>Tip</servlet-name>
 <url-pattern>/tip</url-pattern>
 </servlet-mapping>
 
 <servlet>
 <servlet-name>Tip2</servlet-name>
 <servlet-class>com.test.Tip2</servlet-class>
 </servlet>
 
 <servlet-mapping>
 <servlet-name>Tip2</servlet-name>
 <url-pattern>/tip2</url-pattern>
 </servlet-mapping>

直接访问tip并转发，同一请求，Request不变 

显示如下

Request值为Request
Session值为Session
Context值为Context
----分界线----

同窗口直接访问tip2,Request为空，其他正常

Request值为null
Session值为Session
Context值为Context
----分界线----

同项目换浏览器直接访问tip2，只有Context存在

Request值为null
Session值为null
Context值为Context
----分界线----

xml中定义session的存活时间，需要浏览器cookies开启支持

<session-config>
 <session-timeout>30</session-timeout>
 </session-config>

 Anr-C 2016.10.21