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过滤器的使用实现网站访问计数器

2017-02-24 16:00 447 查看

一、创建过滤器需要使用javax.servlet.Filter接口，同时实现Filter接口的3个方法。

CountFilter:

package com.home.web;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;

public class CountFilter implements Filter{

// 记录来访数量
private int count;

@Override
public void destroy() {
}

@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
count++;
HttpServletRequest req = (HttpServletRequest) request;
ServletContext context = req.getSession().getServletContext();
context.setAttribute("count", count);// 保存到ServletContext中
chain.doFilter(request, response);
}

@Override
public void init(FilterConfig filterConfig) throws ServletException {
String param = filterConfig.getInitParameter("count");// 获取初始值
count = Integer.valueOf(param);
}

}

二、配置
<filter>
<filter-name>CountFilter</filter-name>
<filter-class>com.home.web.CountFilter</filter-class>
<init-param>
<param-name>count</param-name>
<param-value>5000</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>CountFilter</filter-name>
<url-pattern>/index.jsp</url-pattern>
</filter-mapping>

index.jsp：
<%@page import="java.net.URLDecoder"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>起始页</title>
</head>
<body>
欢迎光临，
<br> 您是本站的第【
<%=application.getAttribute("count")%>
】为访客！
</body>
</html>

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