1. 创建动态网站项目02_Context，新建初始化计数器的Servlet类InitServlet。并且在该Servlet的init方法中进行ServletContext对象属性的设置与初始化，InitServlet类代码如下：

package com;
import java.io.IOException;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
 1. Servlet implementation class InitServlet
 */
public class InitServlet extends HttpServlet {
    @Override
    public void init(ServletConfig config) throws ServletException {
        // TODO Auto-generated method stub
        System.out.println("this is the init method.this is only init at the first and only once");
        super.init(config);
        ServletContext servletContext =config.getServletContext();
        servletContext.setAttribute("requestNum", 0);
    }
    private static final long serialVersionUID = 1L;
    /**
     * @see HttpServlet#HttpServlet()
     */
    public InitServlet() {
        super();
        System.out.println("This is the constructor....");
        // TODO Auto-generated constructor stub
    }
    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.getWriter().append("Served at: ").append(request.getContextPath());
    }
    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }
}

1. web.xml文件内容如下：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>02_Context</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <description></description>
    <display-name>InitServlet</display-name>
    <servlet-name>InitServlet</servlet-name>
    <servlet-class>com.InitServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>InitServlet</servlet-name>
    <url-pattern>/InitServlet</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>Servlet1</display-name>
    <servlet-name>Servlet1</servlet-name>
    <servlet-class>com.Servlet1</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Servlet1</servlet-name>
    <url-pattern>/Servlet1</url-pattern>
  </servlet-mapping>
</web-app>

1. 新建Servlet1.java类

   package com;
   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;
   /**
   * Servlet implementation class Servlet1
   */
   public class Servlet1 extends HttpServlet {
   private static final long serialVersionUID = 1L;
   /**
    * @see HttpServlet#HttpServlet()
    */
   public Servlet1() {
       super();
       // TODO Auto-generated constructor stub
   }
   /**
    * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
    */
   protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       // TODO Auto-generated method stub
       ServletContext servletContext = this.getServletContext();
       Object number = servletContext.getAttribute("requestNumber");
       int i = 0;
       if (number == null)
           servletContext.setAttribute("requestNumber", 0);
       else {
           i = new Integer(number.toString());
           i++;
           servletContext.setAttribute("requestNumber", i);
       }
       PrintWriter writer = response.getWriter();
       writer.println("I'm Servlet1, the request number is " +i);
   }
   /**
    * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
    */
   protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       // TODO Auto-generated method stub
       doGet(request, response);
   }
   }

   • 运行程序结果为：