自定义标签 —— 实现时间转换和输出功能

<!-- https://mvnrepository.com/artifact/javax.servlet.jsp/jsp-api -->
<dependency>
    <groupId>javax.servlet.jsp</groupId>
    <artifactId>jsp-api</artifactId>
    <version>2.2</version>
    <scope>provided</scope>
</dependency>

@SuppressWarnings("serial")  
public class DateConvert extends TagSupport {  
    private String longTime;  
    public String getLongTime() {  
        return longTime;  
    }  
    public void setLongTime(String longTime) {  
        this.longTime = longTime;  
    }  
  
    @Override  
    public int doStartTag() throws JspException {  
        long l = 0l;  
        if(longTime!=null && !longTime.equals("")){  
            l = Long.parseLong(longTime);  
        }  
        Date date = new Date(l);  
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");  
        String targetTime = format.format(date);  
        try {  
            super.pageContext.getOut().write(targetTime);  
            super.pageContext.getOut().write("<br/>");  
            super.pageContext.getOut().write("123123");  
        } catch (IOException e) {  
            e.printStackTrace();  
        }  
        return super.doStartTag();  
    }  
}

<?xml version="1.0" encoding="UTF-8"?>  
<!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN"  
                        "http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd">  
<taglib>  
    <tlib-version>1.0</tlib-version>  
    <jsp-version>1.2</jsp-version>  
    <short-name>dateConvert</short-name>  
    <uri>/dateConvert</uri>  

    <tag>  
        <name>longStr</name>  
        <tag-class>spittr.tag.DateConvert</tag-class>  
        <body-content>JSP</body-content>  
        <attribute>  
            <name>longTime</name>  
            <required>true</required><!-- 表示该属性，一定要使用 -->  
            <rtexprvalue>true</rtexprvalue><!-- 属性是否能用表达式 -->  
        </attribute>  
    </tag>  
</taglib>

<jsp-config>  
    <taglib>  
        <taglib-uri>/dateConvert</taglib-uri>    
        <taglib-location>./tag/dateConvert.tld</taglib-location>    
    </taglib>    
</jsp-config>

<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%>  
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>  
<%@ taglib uri="/dateConvert" prefix="ct" %>  
<h1>Register</h1>  
<form method="post" enctype="multipart/form-data">  
    First Name:<input type="text" name="firstName"/><br/>  
    Last Name:<input type="text" name="lastName"/><br/>  
    Username:<input type="text" name="userName"/><br/>  
    Password:<input type="password" name="password"/><br/>  
    file:<input type="file" name="profilePicture" accept="image/jpeg,image/png,image/gif"><br/>  
    <ct:longStr longTime="1314842011312"></ct:longStr>  
    <input type="submit" value="Register"/>  
</form>