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>imageRedirectFilter</filter-name>        <filter-class>            com.helloweenvsfei.filter.ImageRedirectFilter        </filter-class></filter><filter-mapping>        <filter-name>imageRedirectFilter</filter-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：