<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"

         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"

         version="4.0">

    <filter>

        <filter-name>imgFilter</filter-name>

        <filter-class>com.zn.ImageFilter</filter-class>

    </filter>

    <filter-mapping>

        <filter-name>imgFilter</filter-name>

        <url-pattern>/img/*</url-pattern>

    </filter-mapping>

</web-app>

package com.zn;

import javax.servlet.*;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.io.IOException;

public class ImageFilter implements Filter {

    @Override

    public void init(FilterConfig filterConfig) throws ServletException {

        System.out.println("过滤器启动！");

    }

    @Override

    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        System.out.println("走了吗");

        //获取到当前请求的连接地址和上一个发送请求的地址

        HttpServletRequest request=(HttpServletRequest)servletRequest;

        HttpServletResponse response=(HttpServletResponse)servletResponse;

        //获取上一个发送请求的连接

        String referer=request.getHeader("Referer");

        String serverName = request.getServerName();

        System.out.println(referer+"\thhhh\t"+serverName);

        if (referer==null||!referer.contains(serverName)){

            request.getRequestDispatcher("/img/ff.png").forward(request,response);

            return;

        }

        //放行

        filterChain.doFilter(request,response);

    }

    @Override

    public void destroy() {

        System.out.println("过滤器销毁！");

    }

}