           JSP Scripting Elements ( - means which has been finished)
--------------------------------------------------
      -  Expressions   <%= expression %>
      -  Scriptlets    <% code%>
      -  Declarations  <%! variables or methods %>
         JSP directive <%@ page session="true" %>
           - <%@ page contentType="MIME-Type;charset=Character-Set" %>
           -  <%@ page import="java.util.*,coreservlets.*" %>
            <%@ page contentType="text/plain" %>
            <%@ page isThreadSafe="false" %>s
            <%@ page session="false" %>
            <%@ page buffer="sizekb" %>
            <%@ page extends="package.class" %>
            <%@ page errorPage="Relative URL" %>
            <%@ page isErrorPage="true" %>

        page directive
        include directive
        taglib directive

        JSP standard action
        <jsp:useBean>
        <jsp:setProperty>
        <jsp:getProperty>
        <jsp:forward>
        <jsp:include>
        <jsp:param>
        <jsp:plugparams>


        request  object
        response object
        out object
        session object
        pageContext object
        application object
        page object
        config object
        exception object


   /*
   * import java.io.*;
   import javax.servlet.*;
   import javax.servlet.http.*;

   // 扩展 HttpServlet 类
   public class HelloWorld extends HttpServlet {

     private String message;

     public void init() throws ServletException
     {
         // 执行必需的初始化
         message = "Hello World";
     }

     public void doGet(HttpServletRequest request,
                       HttpServletResponse response)
               throws ServletException, IOException
     {
         // 设置响应内容类型
         response.setContentType("text/html");

         // 实际的逻辑是在这里
         PrintWriter out = response.getWriter();
         out.println("<h1>" + message + "</h1>");
     }

     public void destroy()
     {
         // 什么也不做
     }
   }*/