防盗链接

原理图：

 

请求头里的referer

 

servlet代码

public void doGet(HttpServletRequest request , HttpServletResponse response)
    throws ServletException, IOException {
    //refered 属性
    String referer = request .getHeader("referer" );
    if (
        referer != null
        && referer.equals("http://localhost:8080/day07_practise/index.html" )){
        //允许访问
        request .getRequestDispatcher("/download.html" ).forward(request , response);
        }else {
        //盗链，去看广告吧
        request .getRequestDispatcher( "/ad.html" ).forward(request , response);
    }
}