Spring Boot:创建自定义Jsp标记-找不到标记库

package com.example.demo.tags;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.SimpleTagSupport;
import java.io.IOException;

public class CustomTagHandler extends SimpleTagSupport {

    @Override
    public void doTag() throws JspException, IOException {
        getJspContext().getOut().write("This is a custom tag");
    }
}

package com.example.demo;

import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.ImportResource;

@Configuration
@ImportResource("classpath:CustomTagLibrary.xml")
public class AppConfig {
}

<?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/web-jsptaglibrary_2_0.xsd"
        version="2.0">
    <tlib-version>1.0</tlib-version>
    <short-name>custom</short-name>
    <uri>http://example.com/custom</uri>
    <tag>
        <name>customTag</name>
        <tag-class>com.example.demo.tags.CustomTagHandler</tag-class>
        <body-content>empty</body-content>
    </tag>
</taglib>

<%@ taglib prefix="custom" uri="http://example.com/custom" %>

<custom:customTag/>