JSP脚本元素和注释复习总结示例

2024-09-05 00:17:49

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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：

复制代码代码如下:
<html>
<head>
<title>JSP Demo</title>
</head>
<body>
<%! int a = 1 ;%>
<%
out.println("a="+a);
a++;
%>
</body>
</html>

结果如下：

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：

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：

复制代码代码如下:
<html>
<head>
<title>test demo</title>
</head>
<body>
<%
String str = "Hello,xiaomo!";
out.println(str);
%>
</body>
</html>

结果如下：

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：

复制代码代码如下:
<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：

复制代码代码如下:
<html>
<head>
<title>test demo</title>
</head>
<body>

<%-- 这是一个JSP注释 --%>
</body>
</html>

结果如下：

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：

复制代码代码如下:
<html>
<head>
<title>test demo</title>
</head>
<body>

</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）：

复制代码代码如下:

/*
* 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/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);
}
}
}