06920170909

1、ServletContext类：web站点的唯一全局对象

1）、是servlet与servlet容器之间的通信接口；

2）、每个servlet应用都会创建一个ServletContext对象与之对应；

3）、ServletContext对象被web应用下的所有servlet共享；

4)、访问web应用资源。


2、ServletContext的使用步骤：


1)、User user = new User("username","passwrod"); request.getServletContext().setAttribute("user",user);


2)、可以在该站点下的任意一个servlet中获取刚才存放在User中的值。request.getServletContext().getAttribute("user",user);


3、代码如下：


package com.tiger.countAccess;

import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.annotation.*;
import javax.servlet.http.*;

/**
 * 06920170909
 * 统计浏览访问次数
 * @author tiger
 * @time 2017年9月9日
 */
@WebServlet("/accessTimesCount")
public class AccessTimesCount extends HttpServlet {
  private static final long serialVersionUID = 1L;

  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    ServletContext application = request.getServletContext();
    //获取远程客户端ip
    String ip = request.getRemoteAddr();
    //将ip存入一个集合中
    List
   
     ips = (List
    
     ) application.getAttribute("ips");
    if (ips == null) {
      //如果为空，则创建
      ips = new ArrayList<>();
    }
    System.out.println("ip = "+ip);
    if (!ips.contains(ip)) {
      if (application.getAttribute("count") == null) {
        application.setAttribute("count", 1);
      }else {
        Integer count = (Integer) application.getAttribute("count");
        count++;
        application.setAttribute("count", count);
      }
      ips.add(ip);
      application.setAttribute("ips", ips);
    }
    response.getWriter().append("count = ").
    append(String.valueOf(application.getAttribute("count")));
  }

  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doGet(request, response);
  }
}
package com.tiger.listener;

import java.io.*;
import javax.servlet.*;
import javax.servlet.annotation.WebListener;
/**
 * 
 * @author tiger
 * @time 2017年9月9日
 */
@WebListener
public class AccessTimesCountListener implements ServletContextListener {

  public AccessTimesCountListener() {  }

  /**
   * 在站点[web应用]解构之前，将浏览访问次数存入到一个文本中
   */
  public void contextDestroyed(ServletContextEvent sce) { 
    System.out.println("AccessTimesCountListener.contextDestroyed()");
    //取得ServletContext操作对象
    ServletContext application = sce.getServletContext();
    //取得数据
    Integer count = (Integer) application.getAttribute("count");
    //创建数据保存路径
    String folder = application.getRealPath(File.separator+"count") + File.separator ;
    File file = new File(folder);
    //如果文件不存在则创建
    if (!file.exists()) {
      file.mkdirs();
    }
    //将数据输出存入本应用下的一个文件夹下的文件中
    try {
      PrintStream ps = new PrintStream(new FileOutputStream(folder +"countAccess.txt"));
      ps.print(count);
      ps.close();
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
  /**
   * @see ServletContextListener#contextInitialized(ServletContextEvent)
   */
  public void contextInitialized(ServletContextEvent sce)  { 
    System.out.println("AccessTimesCountListener.contextInitialized()");
    ServletContext application = sce.getServletContext();
    String folder = application.getRealPath(File.separator+"count")+ File.separator ;
    File file = new File(folder); 
    if(file.exists()) {
      try {
        BufferedReader reader = new BufferedReader(new FileReader(folder + "countAccess.txt"));
        String countstr = reader.readLine();
        System.out.println("contextInitialized--count = "+countstr);
        Integer count = Integer.parseInt(countstr);
        application.setAttribute("count", count);
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }
}