编写自定义EL函数的步骤:
1.编写一个有public的静态方法的java类
2.编写一个标记库描述文件
3.在jsp中使用一个taglib指令
4.使用EL调用函数


我的QQ号:2535279 ，网址：www.javaedu.com.cn
详细请看下面这个例子：

ELFunction.java

public class ELFunction{
    public static String sayHello(){
        return "Hello,world";
    }
    
    public static int max(int x,int y){
        return (i>j)?i:j;
    }
    
    public static String concat(String str1,Stringstr2){
        return str1+str2;
    }

}

WEB-INF/*.tld

<?xml version="1.0" encoding="gb2312"?>
<!DOCTYPE taglib
    PUBLIC "-Sun MicroSystems,INC.//DTD JSP Tag Library 1.2//EN"
    "http:\\java.sun.com\js2ee\dtd\web-jsptaglibrary-1-2.dtd"
>

<taglib>
    <tlib-version>1.0</tlib-version>
    <jsp-version>2.0</jsp-version>
    <short-name>elfn</short-name>
    <uri>myelfunction</url>
    
    <function>
        <name>sayHello</name>
        <function-class>*****</function-class>
        <function-signature>String sayHello()</function-signature>
    </function>
    
    <function>
        <name>max</name>
        <function-class>*****</function-class>
        <function-signature>int max(int,int)</function-signature>
    </function>
    
    <function>
        <name>concat</name>
        <function-class>*****</function-class>
        <function-signature>String concat(java.lang.String,java.lang.String)</function-signature>
    </function>
    
</taglib>    
        
        
*.jsp

<%@ taglib uri="myelfunction" prefix ="my"%>

${my:sayHello()}
${my:max(20,30)}
${my:concat("Hello","Spring")}