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[JSP] JSP脚本元素和注释复习总结示例

开发技术 开发技术 发布于:2021-10-23 21:17 | 阅读数:511 | 评论:0

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:
DSC0000.gif
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:
DSC0001.gif
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:
DSC0002.gif
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:
DSC0003.gif
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:
DSC0004.gif
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); 
} 
} 
}
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