Java中实现反盗链Filter

反盗链Filter实现这样一种效果，如果其他的网站引用本网站的图片资源，将会显示一个错误的图片。只有本站内的网页引用时，图片才会正确显示。即在图片实现之前对request进行验证，看客户请求是否来自本网站内，代码如下：
ImageRedirectFilter.java

package com.helloweenvsfei.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.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ImageRedirectFilter implements Filter {

    public void init(FilterConfig config) throws ServletException {
    }

    public void doFilter(ServletRequest req, ServletResponse res,
            FilterChain chain) throws IOException, ServletException {

        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;

        // 禁止缓存
        response.setHeader("Cache-Control", "no-store");
        response.setHeader("Pragrma", "no-cache");
        response.setDateHeader("Expires", 0);

        // 链接来源地址
        String referer = request.getHeader("referer");

        if (referer == null || !referer.contains(request.getServerName())) {

            /**
             * 如果 链接地址来自其他网站，则返回错误图片
             */
            request.getRequestDispatcher("/error.gif").forward(request,
                    response);

        } else {

            /**
             * 图片正常显示
             */
            chain.doFilter(request, response);
        }

    }

    public void destroy() {
    }
}

该Filter从request信息头中获取请求来自何方。Filter的配置代码如下：

<filter>
        <filter-name>imageRedirectFilterfilter-name>
        <filter-class>
            com.helloweenvsfei.filter.ImageRedirectFilter
        filter-class>
filter>
<filter-mapping>
        <filter-name>imageRedirectFilterfilter-name>
        <url-pattern>/images/*url-pattern>
        <url-pattern>/upload/images/*url-pattern>
filter-mapping>

该Filter配置为仅对/images/与/upload/images/下的所有资源有效。运行效果如下图所示：