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


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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")}