// 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"); 

  System.out.println("refer is"+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); 

  }