JSP2.0自定义标签

来源：互联网发布：张成泽犬决知乎编辑：程序博客网时间：2024/04/30 17:09

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

[java] view plaincopy

<%@ tag import="java.util.*" import="java.text.*" %>
<%
DateFormat df = DateFormat.getDateInstance(DateFormat.LONG);
Date d = new Date(System.currentTimeMillis());
out.println(df.format(d));
%>

[html] view plaincopy

<%@ 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

[java] view plaincopy

<%@ 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));
%>

[html] view plaincopy

<%@ 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

[java] view plaincopy

<%@ 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/>

[html] view plaincopy

<%@ 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：

[java] view plaincopy

<%@ 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/>

[html] view plaincopy

<%@ 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

[html] view plaincopy

<?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>

[html] view plaincopy

<?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javadisplay-name标签名small-iconfor toolslarge-iconfor toolsdescription标签作用描述exampleinformal description of how the tag is used<jsp:directive:attribute>的可选属性

name属性名requiredtrue or falsertexprvaluetrue or false - 指定是否支持运行时表达式type值类型 - 默认是java.lang.Stringfragmenttrue 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-attributeSpecifies 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.aliasA 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.declareIndicates 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

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