自定义标签 —— 实现时间转换和输出功能

第一步：导入jar包  jsp-api-2.2-sources.jar

<!-- 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>

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>