JSP技术模型(四)JSP脚本元素和注释

今天复习了JSP脚本元素和注释部分,案例写出来,大家自己调试下,整体总结如下,

1、JSP申明语句:

<%!  申明语句 %>

使用申明语句的变量为全局变量,多个用户执行此JSP页面,将共享该变量。

如:

<html>
<head>
<title>JSP Demo</title>
</head>
<body>
<%!  int a = 1 ;%>
<%
out.println("a="+a);
a++;
%>
</body>

</html>

结果如下:

JSP技术模型(四)JSP脚本元素和注释_第1张图片

再次刷新,会发现如下a的值加一了,因为变量a是全局变量,a++运算多次累计,多用客服端共享:

JSP技术模型(四)JSP脚本元素和注释_第2张图片

2、JSP Scriptlets:

<% Java代码%>

在JSP Scriptlets中可包含多个语句,如:方法,变量, 表达式等;

如:

<html>
<head>
<title>test demo</title>
</head>
<body>
<% 
String str = "Hello,xiaomo!";
out.println(str);
      %>
</body>

</html>

结果如下:

JSP技术模型(四)JSP脚本元素和注释_第3张图片

3、JSP表达式:

<%=  Java代码  %>

一种简单的输出形式,必须有一个可以输出的值,表达式中的代码会首先执行,然后转换成字符串显示到页面。

如:

<html>
<head>
<title>test demo</title>
</head>
<body>
<% String str = "Hello,xiaomo!";  %>
<%= str %>
</body>

</html>

结果如下:


4、JSP注释:

<!--  --> HTML注释,会显示于客户端;

<%--   --%>JSP注释,不会显示于客户端;

如:

<html>
<head>
<title>test demo</title>
</head>
<body>
<!-- 这是一个网页注释 -->
<%-- 这是一个JSP注释 --%>
</body>
</html>

结果如下:

JSP技术模型(四)JSP脚本元素和注释_第4张图片

大家发现都没有什么显示,点击浏览器右键查看源码可以看到网页注释是在的,JSP注释没有,这个只有在JSP源码才能看到:

<html>
  <head>
  <title>test demo</title>
  </head>
  <body>
  <!-- 这是一个网页注释 -->
   
  </body>
  </html>

应该很多人都知道,JSP页面是转译成Servlet后在通过服务器转换成html代码发送到客户端显示的,下面给大家看下本案例的JSP页面转换成Servlet后的源码(其中红色标注为转换成前台的html代码):

/*
 * Generated by the Jasper component of Apache Tomcat
 * Version: Apache Tomcat/7.0.34
 * Generated at: 2013-07-03 01:27:37 UTC
 * Note: The last modified time of this file was set to
 *       the last modified time of the source file after
 *       generation to assist with modification tracking.
 */
package org.apache.jsp;


import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;


public final class HelloXiaoMo_jsp extends org.apache.jasper.runtime.HttpJspBase
    implements org.apache.jasper.runtime.JspSourceDependent {


  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\n");
      out.write("<html>\r\n");
      out.write("\t<head>\r\n");
      out.write("\t\t<title>test demo</title>\r\n");
      out.write("\t</head>\r\n");
      out.write("\t<body>\r\n");
      out.write("\t\t<!-- 这是一个网页注释 -->\r\n");
      out.write("\t\t");
      out.write("\r\n");
      out.write("\t</body>\r\n");
      out.write("</html>");


    } 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);
        else throw new ServletException(t);
      }
    } finally {
      _jspxFactory.releasePageContext(_jspx_page_context);
    }
  }
}

出处:http://blog.csdn.net/cl05300629/article/details/9229445 作者:伫望碧落

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