EL表达式（三）自定义 EL 表达式

时间：2023-03-09 16:38:51
EL表达式（三）自定义 EL 表达式

自定义EL函数(静态方法):
编写步骤:
1.编写一个Java类，提供一个静态方法
import java.util.List;
public class GetLength {
public static Integer getLength(List list){

return list.size();
}
}

2.在WEB-INF目录下建立一个拓展名为tld（描述文件）的xml文件
<?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">

<description>this method can get a list length</description>
<display-name>getlength</display-name>
<tlib-version>1.1</tlib-version>
<short-name>myfn</short-name> <!-- 标准访问前缀 -->
<uri>http://www.sdxbxx.con/getLength</uri>
<function> <!-- 定义函数 -->
<description>this method can get a list length</description>
<name>getLength</name>
<function-class>cn.gs.wwg.el.GetLength</function-class>
<function-signature>java.lang.Integer getLength(java.util.List)</function-signature>
</function>
</taglib>
3.(可选)告知应用tld文件和tld中的uri对应
<jsp-config>
<taglib>
<taglib-uri>http://www.sdxbxx.con/getLength</taglib-uri>
<taglib-location>/WEB-INF/getLength.tld</taglib-location>
</taglib>
</jsp-config>

2.在WEB-INF目录下建立一个拓展名为tld(标签描述文件)的xml文件
3.(可选)告知应用tld文件和tld中的uri对应

1. Java

 package cn.gs.ly.mvc.domain;

 import java.util.List;

 public class GetLength {

     public static Integer getLength(List list){

         return list.size();

     }

 }

2. jsp

 <%@page import="java.util.HashMap"%>

 <%@page import="java.util.Map"%>

 <%@page import="java.util.ArrayList"%>

 <%@page import="java.util.List"%>

 <%@page import="cn.gs.ly.mvc.domain.Person"%>

 <%@ taglib uri="/WEB-INF/getLength.tld" prefix="myfn" %>

 <%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %>

 <%@ taglib uri="http://www.liuyang.com/getLength" prefix="myfn1" %>

 <%@ page language="java" contentType="text/html" pageEncoding="UTF-8"%>

 <!DOCTYPE html>

 <html>

 <head>

 <title>Insert title here</title>

 </head>

 <body>

     <%

         List list = new ArrayList();

         list.add("a");

         list.add("b");

         list.add("c");

         pageContext.setAttribute("list", list);

     %>

     ${myfn:getLength(list)}<hr/>

     ${fn:contains("abcd","ab") }<hr/>

     ${fn:contains("abcd","abd") }<hr/>

     ${fn:split("2018-1-4--14:41:140","-:")[0] }<hr/>

     ${fn:split("2018-1-4--14:41:140","-:")[1] }<hr/>

     ${fn:split("2018-1-4--14:41:140","-:")[2] }<hr/>

     ${fn:split("2018-1-4--14:41:140","-:")[3] }<hr/>

     ${fn:split("2018-1-4--14:41:140","-:")[4] }<hr/>

     ${fn:split("2018-1-4--14:41:140","-:")[5] }<hr/>

     ${fn:split("2018-1-4--14:41:140","-:")[6] }<hr/>

 </body>

 </html>

3. 在WEB-INF目录下建立一个拓展名为tld（描述文件）的xml文件

 <?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">

       <description>this method can get a List length</description>

       <display-name>getLength</display-name>

       <tlib-version>1.1</tlib-version>

       <short-name>myfn</short-name>

       <uri>http://www.liuyang.com/getLength</uri>

       <function>

         <description>this method can get a List length </description>

         <name>getLength</name>

         <function-class>cn.gs.ly.mvc.domain.GetLength</function-class>

         <function-signature>java.long.Integer getLength(java.util.List)</function-signature>

       </function>

 </taglib>

4. 配置web.xml 文件

 <?xml version="1.0" encoding="UTF-8"?>

 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">

   <display-name>WEB2018</display-name>

   <welcome-file-list>

     <welcome-file>index.html</welcome-file>

     <welcome-file>index.htm</welcome-file>

     <welcome-file>index.jsp</welcome-file>

     <welcome-file>default.html</welcome-file>

     <welcome-file>default.htm</welcome-file>

     <welcome-file>default.jsp</welcome-file>

   </welcome-file-list>    

       <context-param><!-- 初始化参数 -->

           <param-name>info</param-name>

           <param-value>value_liuyang</param-value>

       </context-param>     

       <jsp-config>

           <taglib>

               <taglib-uri>http://www.liuyang.com/getLength</taglib-uri>

               <taglib-location>/WEB-INF/getLength.tld</taglib-location>

           </taglib>

       </jsp-config>

 </web-app>

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