?xml version="1.0" encoding="UTF-8" ?>
taglib xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
  http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd"
  version="2.1">
  !-- 定义版本 -->
  tlib-version>1.0/tlib-version>
  !-- 定义名字 -->
  short-name>apsliyuan/short-name>
  !-- 定义uri -->
  uri>http://my.oschina.net/aps/uri>
  !-- 定义自己的类 -->
  tag>
    !-- name 就是在jsp中显示的标签名字，aps:hellowTag/> -->
    name>hellowTag/name>
    !-- 自己写的标签类的完整路径 -->
    tag-class>cn.itcast.apsliyuan.tag.HellowtTag/tag-class>
    !-- jsp中主题中是不是要显示内容，有四个属性， 如果为empty的话。在jsp页面中标签就不能定义自己的内容了，否则会报 Servlet.service() 
      for servlet jsp threw exception org.apache.jasper.JasperException: /index.jsp(12,8) 
      According to TLD, tag aps:hellowTag must be empty, but is not 异常
     -->
    body-content>JSP/body-content>
  /tag>
!-- 
  这里没有写属性，有时间补上
 -->
  tag>
    name>ApsliyuanTag/name>
    tag-class>cn.itcast.apsliyuan.tag.ApsliyuanTag/tag-class>
    body-content>JSP/body-content>
  /tag>
/taglib>

//自定义标签的类
package cn.itcast.apsliyuan.tag;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.TagSupport;
public class HellowtTag extends TagSupport{
  /**
   * 
   */
  private static final long serialVersionUID = 1781703371130382609L;
  @Override
  public int doStartTag() throws JspException {
    // TODO Auto-generated method stub
    JspWriter out = pageContext.getOut();
    SimpleDateFormat format=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    try {
      out.print(format.format(new Date()));
    } catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
    return EVAL_BODY_INCLUDE;
  }
  @Override
  public int doEndTag() throws JspException {
    // TODO Auto-generated method stub
    JspWriter out = pageContext.getOut();
    try {
      out.print("br/> hr/>标签执行完毕了");
    } catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
    return EVAL_PAGE;
  }
}

//jsp中引入自己定义的标签
%@ page language="java" contentType="text/html; charset=UTF-8"
  pageEncoding="UTF-8"%>
  %@taglib uri="http://my.oschina.net/aps" prefix="aps" %>
  %@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
html>
head>
meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
title>index.jsp/title>
/head>
body>
  现在的时间是：aps:hellowTag> /aps:hellowTag>br/>
  hr/>
  我爱的人是： aps:ApsliyuanTag/>
/body>
/html>

//看看TagSupport中的源代码， 这个是适配器模式
public class TagSupport implements IterationTag, Serializable {
  public static final Tag findAncestorWithClass(Tag from,
      // TCK signature test fails with generics
      @SuppressWarnings("unchecked")
      Class klass) {
  boolean isInterface = false;
  if (from == null ||
    klass == null ||
    (!Tag.class.isAssignableFrom(klass) 
     !(isInterface = klass.isInterface()))) {
    return null;
  }
  for (;;) {
    Tag tag = from.getParent();
    if (tag == null) {
    return null;
    }
    if ((isInterface  klass.isInstance(tag)) ||
      klass.isAssignableFrom(tag.getClass()))
    return tag;
    else
    from = tag;
  }
  }
  /**
   * Default constructor, all subclasses are required to define only
   * a public constructor with the same signature, and to call the
   * superclass constructor.
   *
   * This constructor is called by the code generated by the JSP
   * translator.
   */
  public TagSupport() { }
  /**
   * Default processing of the start tag, returning SKIP_BODY.
   *
   * @return SKIP_BODY
   * @throws JspException if an error occurs while processing this tag
   *
   * @see Tag#doStartTag()
   */
  public int doStartTag() throws JspException {
    return SKIP_BODY;
  }
  /**
   * Default processing of the end tag returning EVAL_PAGE.
   *
   * @return EVAL_PAGE
   * @throws JspException if an error occurs while processing this tag
   *
   * @see Tag#doEndTag()
   */
  public int doEndTag() throws JspException {
  return EVAL_PAGE;
  }
  /**
   * Default processing for a body.
   *
   * @return SKIP_BODY
   * @throws JspException if an error occurs while processing this tag
   *
   * @see IterationTag#doAfterBody()
   */
  public int doAfterBody() throws JspException {
  return SKIP_BODY;
  }
  // Actions related to body evaluation
  /**
   * Release state.
   *
   * @see Tag#release()
   */
  public void release() {
  parent = null;
  id = null;
  if( values != null ) {
    values.clear();
  }
  values = null;
  }
  /**
   * Set the nesting tag of this tag.
   *
   * @param t The parent Tag.
   * @see Tag#setParent(Tag)
   */
  public void setParent(Tag t) {
  parent = t;
  }
  /**
   * The Tag instance most closely enclosing this tag instance.
   * @see Tag#getParent()
   *
   * @return the parent tag instance or null
   */
  public Tag getParent() {
  return parent;
  }
  /**
   * Set the id attribute for this tag.
   *
   * @param id The String for the id.
   */
  public void setId(String id) {
  this.id = id;
  }
  /**
   * The value of the id attribute of this tag; or null.
   *
   * @return the value of the id attribute, or null
   */
  public String getId() {
  return id;
  }
  /**
   * Set the page context.
   *
   * @param pageContext The PageContext.
   * @see Tag#setPageContext
   */
  public void setPageContext(PageContext pageContext) {
  this.pageContext = pageContext;
  }
  /**
   * Associate a value with a String key.
   *
   * @param k The key String.
   * @param o The value to associate.
   */
  public void setValue(String k, Object o) {
  if (values == null) {
    values = new HashtableString, Object>();
  }
  values.put(k, o);
  }
  /**
   * Get a the value associated with a key.
   *
   * @param k The string key.
   * @return The value associated with the key, or null.
   */
  public Object getValue(String k) {
  if (values == null) {
    return null;
  } else {
    return values.get(k);
  }
  }
  /**
   * Remove a value associated with a key.
   *
   * @param k The string key.
   */
  public void removeValue(String k) {
  if (values != null) {
    values.remove(k);
  }
  }
  /**
   * Enumerate the keys for the values kept by this tag handler.
   *
   * @return An enumeration of all the keys for the values set,
   *   or null or an empty Enumeration if no values have been set.
   */
  public EnumerationString> getValues() {
  if (values == null) {
    return null;
  }
  return values.keys();
  }
  // private fields
  private  Tag     parent;
  private  HashtableString, Object>  values;
  /**
   * The value of the id attribute of this tag; or null.
   */
  protected String   id;
  // protected fields
  /**
   * The PageContext.
   */
  protected PageContext pageContext;
}