1，定义java静态方法，FunctionDemo，有小写转大写的功能
package com.itheima.domain;
public class FunctionDemo {
public static String toUpperCase(String string){
return string.toUpperCase();
}
}
2，编辑xml文件，扩展名为tld
需要指定类的详细名称，带包名，方法的详细信息，返回值+方法名+参数，和访问路径uri，在页面中导入这个uri才能使用，前缀
<?xml version="1.0" encoding="UTF-8"?>
<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"
version="2.0">
<tlib-version>1.0</tlib-version>
<short-name>itheima</short-name>
<uri>http://www.heima.com/jsp/myfun</uri>
<function>
<description>
toUpperCase
</description>
<name>toUpperCase</name>
<function-class>com.itheima.domain.FunctionDemo</function-class>
<function-signature>java.lang.String toUpperCase(java.lang.String)</function-signature>
<example>
<itheima:toUpperCase("aavvavb")>
</example>
</function>
</taglib>
3在页面中使用，需要用taglib标签，指定uri和前缀
<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8"%>
<%@taglib uri="http://www.heima.com/jsp/myfun" prefix="itheima" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Insert title here</title>
</head>
<body>
${itheima:toUpperCase("adsafjka") }
</body>
</html>