Filter过滤器实现统计访问量和统一编码格式

爱被打了一巴掌 2024-02-18 23:11 22阅读 0赞

## 1. 什么是过滤器 ##

Servlet过滤器实质上就是在web应用服务器上的一个web应用组件，用于拦截客户端(浏览器) 与目标资源的请求，并对这些请求进行一定过滤处理再发送给目标资源。

每一个过滤器对象都要直接或间接地实现Filter接口，在Filter接口中定义了3个方法，分别为init()方法、doFilter()方法和destroy()方法。

过滤器中的init()方法用于对过滤器的初始化进行处理；

destroy()方法是过滤器的销毁方法，主要用于释放资源；

对于过滤处理的业务逻辑需要编写到doFilter()方法中，在请求过滤处理后，需要调用chain参数的doFilter()方法将请求向下传递给下一过滤器或目标资源。

## 2. Filter过滤器实现统计访问量和统一编码格式 ##

![70][]

### 2.1 index.jsp ###

<%@ page language="java" contentType="text/html; charset=UTF-8"
        pageEncoding="UTF-8"%>
    <!DOCTYPE html>
    <html>
    <head>
    <meta charset="UTF-8">
    <title>Insert title here</title>
    </head>
    <body>
    	<h2>
    	欢迎光临,<br>
    	您是本站的第[
    	<%= application.getAttribute("count") %>
    	]位访客!
    	</h2>
    	
    	<form action="TestServlet" method="post">
    	  <input type="text" name="age">
    	  <input type="submit">
    	
    	</form>
    	
    </body>
    </html>

### 2.2 CountFilter.java ###

package com.filter;
    
    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.annotation.WebFilter;
    import javax.servlet.http.HttpServletRequest;
    
    /**
     * Servlet Filter implementation class CountFilter
     */
    //@WebFilter("/CountFilter")
    public class CountFilter implements Filter {
    	
    	//声明来访数量
    	private int count;
    
        /**
         * Default constructor. 
         */
        public CountFilter() {
            // TODO Auto-generated constructor stub
        }
    
    	/**
    	 * @see Filter#destroy()
    	 */
    	public void destroy() {
    		// TODO Auto-generated method stub
    	}
    
    	
    
    	/**
    	 * @see Filter#init(FilterConfig)
    	 */
    	public void init(FilterConfig fConfig) throws ServletException {
    		//获取初始化参数
    		String param =fConfig.getInitParameter("count");
    		//将字符串转换为int
    		count=Integer.valueOf(param);
    	}
    	
    	
    	/**
    	 * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
    	 */
    	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    		
    		//访问数量自增
    		count++;
    		//将ServletRequest转换为HttpServletRequest
    		HttpServletRequest req =(HttpServletRequest)request;
    		//获取ServletContext相当于application
    		ServletContext context = req.getSession().getServletContext();
    		//将来访数量值放入到ServletContext中
    		context.setAttribute("count", count);
    		//向下传递过滤器
    		chain.doFilter(request, response);
    	}
    
    }

### 2.3 CharactorFilter.java ###

package com.filter;
    
    import java.io.IOException;
    import javax.servlet.Filter;
    import javax.servlet.FilterChain;
    import javax.servlet.FilterConfig;
    import javax.servlet.ServletException;
    import javax.servlet.ServletRequest;
    import javax.servlet.ServletResponse;
    //import javax.servlet.annotation.WebFilter;
    
    /**
     * Servlet Filter implementation class CharactorFilter
     */
    //@WebFilter("/CharactorFilter")
    public class CharactorFilter implements Filter {
    	
    	//字符编码
    	String encoding=null;
    
        /**
         * Default constructor. 
         */
        public CharactorFilter() {
            // TODO Auto-generated constructor stub
        }
    
    	/**
    	 * @see Filter#destroy()
    	 */
    	public void destroy() {
    		encoding=null;
    	}
    
    	/**
    	 * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
    	 */
    	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    		// TODO Auto-generated method stub
    		//判断字符编码是否为空
    		if(encoding!=null) {
    			//设置request的编码格式
    			request.setCharacterEncoding(encoding);
    			//设置response的编码格式
    			response.setContentType("text/html;charset="+encoding);
    		}
    		
    		//传给下一过滤器
    		chain.doFilter(request, response);
    	}
    
    	/**
    	 * @see Filter#init(FilterConfig)
    	 */
    	public void init(FilterConfig fConfig) throws ServletException {
    		//获取初始化参数
    		encoding=fConfig.getInitParameter("encoding");
    	}
    
    }

### 2.4 TestServlet.java ###

package com.servlet;
    
    import java.io.IOException;
    import java.io.PrintWriter;
    
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    /**
     * Servlet implementation class TestServlet
     */
    @WebServlet("/TestServlet")
    public class TestServlet extends HttpServlet {
    	private static final long serialVersionUID = 1L;
           
        /**
         * @see HttpServlet#HttpServlet()
         */
        public TestServlet() {
            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
    		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
    		String age= request.getParameter("age");
    
    		PrintWriter out =response.getWriter();
    		out.println(age);
    	}
    
    }

### 2.5 web.xml ###

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
      <display-name>filter123</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>
      <filter>
        <filter-name>CountFilter</filter-name>
        <filter-class>com.filter.CountFilter</filter-class>
        <init-param>
          <param-name>count</param-name>
          <param-value>0</param-value>
        </init-param>
      </filter>
      <filter-mapping>
        <filter-name>CountFilter</filter-name>
        <url-pattern>/index.jsp</url-pattern>
      </filter-mapping>
      <filter>
        <filter-name>CharactorFilter</filter-name>
        <filter-class>com.filter.CharactorFilter</filter-class>
        <init-param>
          <param-name>encoding</param-name>
          <param-value>UTF-8</param-value>
        </init-param>
      </filter>
      <filter-mapping>
        <filter-name>CharactorFilter</filter-name>
        <url-pattern>/*</url-pattern>
      </filter-mapping>
    </web-app>

[70]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/29/7ddfc5c250f34104bfd0147b1e4666f9.png