JSP2.0自定义标签

JSP1.0中可以通过继承TagSupport或者BodyTagSupport来实现自定义的tag处理方法。

JSP2.0中也支持另外一种更为简单的自定tag的方法，那就是直接讲JSP代码保存成*.tag或者*.tagx的标签定义文件。tag和tagx文件不仅支持经典jsp代码，各种标签模版代码，还支持xml样式的jsp指令代码。

按照约定，tag和tagx文件需要放置在WEB-INF/tags目录下。

下面是一些简单的示例：

1.简单地显示时间time.tag

<%@ tag import="java.util.*" import="java.text.*" %>

<%

  DateFormat df = DateFormat.getDateInstance(DateFormat.LONG);

  Date d = new Date(System.currentTimeMillis());

  out.println(df.format(d));

%>

<%@ taglib prefix="util" tagdir="/WEB-INF/tags" %>

<html>

  <head>

  </head>

  <body>

     Today is <util:time/>.

  </body>

</html>

2.复制字符串多少遍repeater.tag

<%@ attribute name="count" type="java.lang.Integer" required="true" %>

<%@ attribute name="value" type="java.lang.String" required="true" %>

<%!

  private String repeater(Integer count, String s) {

    int n = count.intValue();

    StringBuffer sb = new StringBuffer();

    for (int i = 0; i < n; i++) {

      sb.append(s);

    }

    return sb.toString();

  }

%>

<%

  out.println(repeater(count, value));

%>

<%@ taglib prefix="util" tagdir="/WEB-INF/tags" %>

<html>

  <head>

  </head>

  <body>

    Let's get some sleep! <util:repeater count='${3 * 10}' value='zzz'/>

  </body>

</html>

3.查找省份lookup.tag

<%@ tag import="java.util.*" %>

<%@ attribute name="cityName" required="true" %>

<%@ variable name-given="province" %>

<%@ variable name-given="population" variable-class="java.lang.Integer" %>

<%

  if ("Toronto".equals(cityName)) {

    jspContext.setAttribute("province", "Ontario");

    jspContext.setAttribute("population", new Integer(2553400));

  }

  else if ("Montreal".equals(cityName)) {

    jspContext.setAttribute("province", "Quebec");

    jspContext.setAttribute("population", new Integer(2195800));

  }

  else {

    jspContext.setAttribute("province", "Unknown");

    jspContext.setAttribute("population", new Integer(-1));

  }

%>

<jsp:doBody/>

<%@ taglib prefix="util" tagdir="/WEB-INF/tags" %>

<html>

  <head>

  </head>

  <body>

    <% pageContext.setAttribute("cityName", "Montreal"); %>

    <util:lookup cityName="${cityName}">

      ${cityName}'s province is ${province}.

      ${cityName}'s population is approximately ${population / 1000000} million.

    </util:lookup>

  </body>

</html>

上面的都是使用的经典jsp代码，下面将第3个示例使用其他代码实现：

*使用标签：

<%@ tag import="java.util.*" %>

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<%@ attribute name="cityName" required="true" %>

<%@ variable name-given="province" %>

<%@ variable name-given="population" %>

<c:choose>

  <c:when test="cityName eq 'Toronto'>

    <c:set var="province" value="Ontario"/>

    <c:set var="population" value="2553400"/>

  </c:when>

  <c:when test="cityName eq 'Montreal'>

    <c:set var="province" value="Quebec"/>

    <c:set var="population" value="2195800"/>

  </c:when>

  <c:otherwise>

    <c:set var="province" value="Unknown"/>

    <c:set var="population" value="-1"/>

  </c:otherwise>

</c:choose>

%>

<jsp:doBody/>

<%@ taglib prefix="util" tagdir="/WEB-INF/tags" %>

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<html>

  <head>

  </head>

  <body>

    <c:set var="cityName" value="Montreal"/>

    <util:lookup cityName="${cityName}">

      ${cityName}'s province is ${province}.

      ${cityName}'s population is approximately ${population / 1000000} million.

    </util:lookup>

  </body>

</html>

*使用jsp指令，通常这种方式生成xml格式的文件

<?xml version='1.0'?>

<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page">

	<jsp:directive.tag import="java.util.*"/>

	<jsp:directive.taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"/>

	<jsp:directive.attribute name="cityName" required="true"/>

	<jsp:directive.variable name-given="province"/>

	<jsp:directive.variable name-given="population"/>

	<c:choose>

	  <c:when test="cityName eq 'Toronto'>

	    <c:set var="province" value="Ontario"/>

	    <c:set var="population" value="2553400"/>

	  </c:when>

	  <c:when test="cityName eq 'Montreal'>

	    <c:set var="province" value="Quebec"/>

	    <c:set var="population" value="2195800"/>

	  </c:when>

	  <c:otherwise>

	    <c:set var="province" value="Unknown"/>

	    <c:set var="population" value="-1"/>

	  </c:otherwise>

	</c:choose>

</jsp:root>

<?xml version='1.0'?>

<jsp:root version='2.0'

          xmlns:jsp="http://java.sun.com/JSP/Page"

          xmlns:util="urn:jsptagdir:/WEB-INF/tags"

          xmlns:c="http://java.sun.com/jsp/jstl/core">

  <jsp:directive.page contentType="text/html"/>

	<html>

	  <head>

	  </head>

	  <body>

	    <c:set var="cityName" value="Montreal"/>

	    <util:lookup cityName="${cityName}">

	      ${cityName}'s province is ${province}.

	      ${cityName}'s population is approximately ${population / 1000000} million.

	    </util:lookup>

	  </body>

	</html>

</jsp:root>

附录：

标签文件中常用的指令：

tag	类似JSP page指令，可以用于import常用的java类库等
include	导入其他的标签定义文件
taglib	使用其他标签，如jstl, spring tag, struts tag等等
attribute	定义一个属性
variable	定义一个jsp page中可见的变量，默认范围为NESTED，表示标签内有效。可选项有AT_BEGIN和AT_END

这些指令的可选属性

body-content	标签body的处理方式，可选项： 'empty', 'tagdependent' or 'scriptless'
import	导入使用的java类库
pageEncoding	设置页面编码
isELIgnored	是否忽略el表达式
dynamic-attributes	用于存储自定义属性的map，所谓的自定义属性指：未隐式申明的变量
language	使用的脚本语言，目前必须是java
display-name	标签名
small-icon	for tools
large-icon	for tools
description	标签作用描述
example	informal description of how the tag is used

<jsp:directive:attribute>的可选属性

name	属性名
required	true or false
rtexprvalue	true or false - 指定是否支持运行时表达式
type	值类型 - 默认是java.lang.String
fragment	true or false - 值先传递给容器(false), 直接传给标签处理方法(true)
description	属性描述

<jsp:directive:variable>的可选属性

name-given	变量名（标签使用时的变量名）
name-from-attribute	Specifies the name of an attribute, whose value is the name of the variable that will be available in the calling JSP page. Exactly one of name-given or name-from-attribute must be supplied.
alias	A locally scoped variable which will store the variable's value. Used only with name-from-attribute.
variable-class	变量类.默认是java.lang.String.
declare	Indicates whether the variable is declared in the calling JSP page or tag file. Default is true. Not entirely clear what this means!
scope	变量范围，可选项 AT_BEGIN(标签后jsp page内有效), AT_END(标签后jsp page内有效) and NESTED. NESTED(默认，标签内有效)
description	变量描述

巴特西

JSP2.0自定义标签

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