Http協議（防止盜鏈）

要點就是req.getHeader(“Referer”)

public class ShowServlet extends HttpServlet {

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {

        resp.setContentType("text/html;charset=utf-8");

        PrintWriter out = resp.getWriter();

        //獲取請求頭中的Referer信息---來自哪裏
        String ref = req.getHeader("Referer");
        String str ="";
        if(ref==null){
            str = "請先看廣告!";
        }else{
            if(ref.contains("helloWeb")){
                str = "<img src='imgs/1.jpg'/>"+
                        "<img src='imgs/2.jpg'/>"+
                        "<img src='imgs/3.jpg'/>"+
                        "<img src='imgs/4.jpg'/>湖南城市學院";
            }else{
                str="來自盜連頁面!";
            }
        }
        out.print(str);
    }
}