创建自定义标签，并实现时间转换和输出功能

首先，得导入jar包  jsp-api-2.2-sources.jar

第二步，定义一个用来实现标签功能的java类，例如：DateConvert.java

@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();
}
}

第三步，可在WEB-INF目录下定义一个*.tld文件，例如dateConvert.tld：

<?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>

 第四步，在web.xml文件中引用你的*.tld文件：

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

 第五步，在你的页面引入自定义标签库进行使用，

<%@ 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>