（一）JSP注釋
JSP注釋用於標註程式開發過程中的開發示範。
JSP注釋：<%-- comment--%> 它不會輸出到用戶端
HTML注釋：<!--comment--> 它會輸出到用戶端
(二)JSP聲明
JSP本質是Servlet，Servlet是特殊的ＪＡＶＡ類，所以ＪＳＰ聲明符合JAVA文法。
文法格式：<%!declaration%>
JSP聲明用於聲明變數和方法，可以放在ＪＳＰ中的任何地方。JSP聲明會轉換成對應Servlet中的成員變數或成員方法。
<body>
<%!
public int count;
public String info(){
return "hello";
}
%>
<%out.print(count++ +" "+info()); %>
</body>
對應的Servlet代碼為
package org.apache.jsp;import javax.servlet.*;import javax.servlet.http.*;import javax.servlet.jsp.*;import java.util.*;public final class test1_jsp extends org.apache.jasper.runtime.HttpJspBase implements org.apache.jasper.runtime.JspSourceDependent { public int count; public String info(){ return "hello"; } private static final javax.servlet.jsp.JspFactory _jspxFactory = javax.servlet.jsp.JspFactory.getDefaultFactory(); private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants; private javax.el.ExpressionFactory _el_expressionfactory; private org.apache.tomcat.InstanceManager _jsp_instancemanager; public java.util.Map<java.lang.String,java.lang.Long> getDependants() { return _jspx_dependants; } public void _jspInit() { _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory(); _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig()); } public void _jspDestroy() { } public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response) throws java.io.IOException, javax.servlet.ServletException { final javax.servlet.jsp.PageContext pageContext; javax.servlet.http.HttpSession session = null; final javax.servlet.ServletContext application; final javax.servlet.ServletConfig config; javax.servlet.jsp.JspWriter out = null; final java.lang.Object page = this; javax.servlet.jsp.JspWriter _jspx_out = null; javax.servlet.jsp.PageContext _jspx_page_context = null; try { response.setContentType("text/html;charset=UTF-8"); pageContext = _jspxFactory.getPageContext(this, request, response, null, true, 8192, true); _jspx_page_context = pageContext; application = pageContext.getServletContext(); config = pageContext.getServletConfig(); session = pageContext.getSession(); out = pageContext.getOut(); _jspx_out = out; out.write('\r'); out.write('\n');String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; out.write("\r\n"); out.write("\r\n"); out.write("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">\r\n"); out.write("<html>\r\n"); out.write(" <head>\r\n"); out.write(" <base href=\""); out.print(basePath); out.write("\">\r\n"); out.write(" \r\n"); out.write(" <title>My JSP 'test1.jsp' starting page</title>\r\n"); out.write(" \r\n"); out.write("\t<meta http-equiv=\"pragma\" content=\"no-cache\">\r\n"); out.write("\t<meta http-equiv=\"cache-control\" content=\"no-cache\">\r\n"); out.write("\t<meta http-equiv=\"expires\" content=\"0\"> \r\n"); out.write("\t<meta http-equiv=\"keywords\" content=\"keyword1,keyword2,keyword3\">\r\n"); out.write("\t<meta http-equiv=\"description\" content=\"This is my page\">\r\n"); out.write("\t<!--\r\n"); out.write("\t<link rel=\"stylesheet\" type=\"text/css\" href=\"styles.css\">\r\n"); out.write("\t-->\r\n"); out.write("\r\n"); out.write(" </head>\r\n"); out.write(" \r\n"); out.write(" <body>\r\n"); out.write(" "); out.write("\r\n"); out.write(" ");out.print(count++ +" "+info()); out.write("\r\n"); out.write(" </body>\r\n"); out.write("</html>\r\n"); } catch (java.lang.Throwable t) { if (!(t instanceof javax.servlet.jsp.SkipPageException)){ out = _jspx_out; if (out != null && out.getBufferSize() != 0) try { out.clearBuffer(); } catch (java.io.IOException e) {} if (_jspx_page_context != null) _jspx_page_context.handlePageException(t); } } finally { _jspxFactory.releasePageContext(_jspx_page_context); } }}
總結：
1.JSP聲明文法定義的變數和方法對應於Servlet類的成員變數和方法，所以JSP聲明部分定義的變數和方法可以使用private，public等存取控制符修飾，也可以用static修飾，將其變成類屬性和類方法，但是不能使用abstract修飾聲明部分的方法，因為抽象方法將導致JSP對應Servlet編程抽象類別，從而導致無法執行個體化。
2.開啟多個瀏覽器，甚至可以在不同的機器上開啟瀏覽器來重新整理頁面，將發現所有的用戶端訪問的count是連續的，及所有用戶端共用了同一個count變數。這是因為JSP頁面會編譯成一個Servlet類，每個Servlet在容器中只有一個執行個體：在JSP中聲明的變數是成員變數，成員變數只在建立執行個體時初始化，該變數的值一直儲存，直到執行個體銷毀。
(三)輸出JSP運算式
文法：<%=expression%> ==<%out.println();%> 輸出運算式等同於HTML頁面的元素。
(四)JSP指令碼 <% java code%>
通常來說，所有可執行java代碼都可以通過JSP指令碼嵌入HTML頁面。
1.JSP頁面中，可包含靜態內容，指令，運算式，小指令碼，聲明，標準動作，注釋。
2.expression,script(小指令碼)，declaration統稱之為java指令碼元素-------用來嵌入java代碼
3.小指令碼：在JSP頁面中嵌入一段JAVA代碼
註：指令碼中嵌入的代碼都是局部變數，定位於service方法中。實際上不僅JSP小指令碼部分會轉換成Service方法裡的可執行代碼，JSP頁面裡的所有靜態類容都將由service方法裡輸出語句來輸出，這就是JSP指令碼可以控制JSP頁面中靜態內容的原因。由於JSP指令碼將轉換成Service方法裡的可執行代碼，而java文法不允許在方法裡定義方法，所以JSP指令碼裡面不能定義方法。
Start building with 50+ products and up to 12 months usage for Elastic Compute Service
1 on 1 presale consultation
24/7 Technical Support 6 Free Tickets per Quarter Faster Response
Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.
A comprehensive suite of global cloud computing services to power your business
Payment Methods We Support
