本文探讨了JSP标签的生命周期，包括标签语言的特点、标签库的运作与tld文件的关系、如何创建和配置tld文件，以及在JSP中导入和使用自定义标签的步骤。通过示例展示了标签的执行过程。
1、jsp标签的生命周期
1. 标签语言特点
1、标签库的运作离不开tld文件
2、标签库的标签是定义在tld中的tag标签内（助手类）
<开始标签 属性=“属性值”>标签体</结束标签>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!-- ui标签
控制标签
数据标签-->
<%@ 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>Insert title here</title>
</head>
<body>
<c:set var="name" value="qudamazi"></c:set>
--------------------------
<c:out value="${name}"></c:out>
</body>
</html>
运行结果：
2:uri标签
.2 创建标签库描述文件(tld)，添加自定义标签的配置
注：tld文件必须保存到WEB-INF目录或其子目录
3 在JSP通过taglib指令导入标签库，并通过指定后缀
访问自定义标签
//自定义uri标签
<?xml version="1.0" encoding="UTF-8" ?>
<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"
version="2.0">
<description>Liuyujian 1.1 core library</description>
<display-name>Liuyujian core</display-name>
<tlib-version>1.1</tlib-version>
<short-name>c</short-name>
<uri>/Liuyujian</uri>
<validator>
<description>
Provides core validation features for JSTL tags.
</description>
<validator-class>
org.apache.taglibs.standard.tlv.JstlCoreTLV
</validator-class>
</validator>
<tag>
<description>
Catches any Throwable that occurs in its body and optionally
exposes it.
</description>
<name>catch</name>
<tag-class>org.apache.taglibs.standard.tag.common.core.CatchTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<description>
Name of the exported scoped variable for the
exception thrown from a nested action. The type of the
scoped variable is the type of the exception thrown.
</description>
<name>var</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
</tag>
<tag>
<description>
Simple conditional tag that establishes a context for
mutually exclusive conditional operations, marked by
<when> and <otherwise>
</description>
<name>choose</name>
<tag-class>org.apache.taglibs.standard.tag.common.core.ChooseTag</tag-class>
<body-content>JSP</body-content>
</tag>
<tag>
<description>
Simple conditional tag, which evalutes its body if the
supplied condition is true and optionally exposes a Boolean
scripting variable representing the evaluation of this condition
</description>
<name>if</name>
<tag-class>org.apache.taglibs.standard.tag.rt.core.IfTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<description>
The test condition that determines whether or
not the body content should be processed.
</description>
<name>test</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
<type>boolean</type>
</attribute>
<attribute>
<description>
Name of the exported scoped variable for the
resulting value of the test condition. The type
of the scoped variable is Boolean.
</description>
<name>var</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<description>
Scope for var.
</description>
<name>scope</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
</tag>
<tag>
<description>
Retrieves an absolute or relative URL and exposes its contents
to either the page, a String in 'var', or a Reader in 'varReader'.
</description>
<name>import</name>
<tag-class>org.apache.taglibs.standard.tag.rt.core.ImportTag</tag-class>
<tei-class>org.apache.taglibs.standard.tei.ImportTEI</tei-class>
<body-content>JSP</body-content>
<attribute>
<description>
The URL of the resource to import.
</description>
<name>url</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>
Name of the exported scoped variable for the
resource's content. The type of the scoped
variable is String.
</description>
<name>var</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<description>
Scope for var.
</description>
<name>scope</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<description>
Name of the exported scoped variable for the
resource's content. The type of the scoped
variable is Reader.
</description>
<name>varReader</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<description>
Name of the context when accessing a relative
URL resource that belongs to a foreign
context.
</description>
<name>context</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>
Character encoding of the content at the input
resource.
</description>
<name>charEncoding</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
<tag>
<description>
The basic iteration tag, accepting many different
collection types and supporting subsetting and other
functionality
</description>
<name>forEach</name>
<tag-class>org.apache.taglibs.standard.tag.rt.core.ForEachTag</tag-class>
<tei-class>org.apache.taglibs.standard.tei.ForEachTEI</tei-class>
<body-content>JSP</body-content>
<attribute>
<description>
Collection of items to iterate over.
</description>
<name>items</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
<type>java.lang.Object</type>
</attribute>
<attribute>
<description>
If items specified:
Iteration begins at the item located at the
specified index. First item of the collection has
index 0.
If items not specified:
Iteration begins with index set at the value
specified.
</description>
<name>begin</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
<type>int</type>
</attribute>
<attribute>
<description>
If items specified:
Iteration ends at the item located at the
specified index (inclusive).
If items not specified:
Iteration ends when index reaches the value
specified.
</description>
<name>end</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
<type>int</type>
</attribute>
<attribute>
<description>
Iteration will only process every step items of
the collection, starting with the first one.
</description>
<name>step</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
<type>int</type>
</attribute>
<attribute>
<description>
Name of the exported scoped variable for the
current item of the iteration. This scoped
variable has nested visibility. Its type depends
on the object of the underlying collection.
</description>
<name>var</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<description>
Name of the exported scoped variable for the
status of the iteration. Object exported is of type
javax.servlet.jsp.jstl.core.LoopTagStatus. This scoped variable has nested
visibility.
</description>
<name>varStatus</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
</tag>
<tag>
<description>
Iterates over tokens, separated by the supplied delimeters
</description>
<name>forTokens</name>
<tag-class>org.apache.taglibs.standard.tag.rt.core.ForTokensTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<description>
String of tokens to iterate over.
</description>
<name>items</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
<type>java.lang.String</type>
</attribute>
<attribute>
<description>
The set of delimiters (the characters that
separate the tokens in the string).
</description>
<name>delims</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
<type>java.lang.String</type>
</attribute>
<attribute>
<description>
Iteration begins at the token located at the
specified index. First token has index 0.
</description>
<name>begin</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
<type>int</type>
</attribute>
<attribute>
<description>
Iteration ends at the token located at the
specified index (inclusive).
</description>
<name>end</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
<type>int</type>
</attribute>
<attribute>
<description>
Iteration will only process every step tokens
of the string, starting with the first one.
</description>
<name>step</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
<type>int</type>
</attribute>
<attribute>
<description>
Name of the exported scoped variable for the
current item of the iteration. This scoped
variable has nested visibility.
</description>
<name>var</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<description>
Name of the exported scoped variable for the
status of the iteration. Object exported is of
type
javax.servlet.jsp.jstl.core.LoopTag
Status. This scoped variable has nested
visibility.
</description>
<name>varStatus</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
</tag>
<tag>
<description>
Like <%= ... >, but for expressions.
</description>
<name>out</name>
<tag-class>org.apache.taglibs.standard.tag.rt.core.OutTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<description>
Expression to be evaluated.
</description>
<name>value</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>
Default value if the resulting value is null.
</description>
<name>default</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>
Determines whether characters <,>,&,'," in the
resulting string should be converted to their
corresponding character entity codes. Default value is
true.
</description>
<name>escapeXml</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
<tag>
<description>
Subtag of <choose> that follows <when> tags
and runs only if all of the prior conditions evaluated to
'false'
</description>
<name>otherwise</name>
<tag-class>org.apache.taglibs.standard.tag.common.core.OtherwiseTag</tag-class>
<body-content>JSP</body-content>
</tag>
<tag>
<description>
Adds a parameter to a containing 'import' tag's URL.
</description>
<name>param</name>
<tag-class>org.apache.taglibs.standard.tag.rt.core.ParamTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<description>
Name of the query string parameter.
</description>
<name>name</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>
Value of the parameter.
</description>
<name>value</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
<tag>
<description>
Redirects to a new URL.
</description>
<name>redirect</name>
<tag-class>org.apache.taglibs.standard.tag.rt.core.RedirectTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<description>
The URL of the resource to redirect to.
</description>
<name>url</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>
Name of the context when redirecting to a relative URL
resource that belongs to a foreign context.
</description>
<name>context</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
<tag>
<description>
Removes a scoped variable (from a particular scope, if specified).
</description>
<name>remove</name>
<tag-class>org.apache.taglibs.standard.tag.common.core.RemoveTag</tag-class>
<body-content>empty</body-content>
<attribute>
<description>
Name of the scoped variable to be removed.
</description>
<name>var</name>
<required>true</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<description>
Scope for var.
</description>
<name>scope</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
</tag>
<tag>
<description>
Sets the result of an expression evaluation in a 'scope'
</description>
<name>set</name>
<tag-class>org.apache.taglibs.standard.tag.rt.core.SetTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<description>
Name of the exported scoped variable to hold the value
specified in the action. The type of the scoped variable is
whatever type the value expression evaluates to.
</description>
<name>var</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<description>
Expression to be evaluated.
</description>
<name>value</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>
Target object whose property will be set. Must evaluate to
a JavaBeans object with setter property property, or to a
java.util.Map object.
</description>
<name>target</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>
Name of the property to be set in the target object.
</description>
<name>property</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>
Scope for var.
</description>
<name>scope</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
</tag>
<tag>
<description>
Creates a URL with optional query parameters.
</description>
<name>url</name>
<tag-class>org.apache.taglibs.standard.tag.rt.core.UrlTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<description>
Name of the exported scoped variable for the
processed url. The type of the scoped variable is
String.
</description>
<name>var</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<description>
Scope for var.
</description>
<name>scope</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
</attribute>
<attribute>
<description>
URL to be processed.
</description>
<name>value</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>
Name of the context when specifying a relative URL
resource that belongs to a foreign context.
</description>
<name>context</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
<tag>
<description>
Subtag of <choose> that includes its body if its
condition evalutes to 'true'
</description>
<name>when</name>
<tag-class>org.apache.taglibs.standard.tag.rt.core.WhenTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<description>
The test condition that determines whether or not the
body content should be processed.
</description>
<name>test</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
<type>boolean</type>
</attribute>
</tag>
</taglib>
执行代码：
执行结果：
3：开发标签
<tag>
<!-- 标签库中的标签 -->
<name>demo</name>
<!-- 是标签运行具体代码，也就是助手类，下面填写助手类的全路径名 -->
<tag-class>Liuyujain.jsp.rest.Demotag</tag-class>
<body-content>JSP</body-content>
<attribute>
<!-- 该标签属性 -->
<name>test</name>
<!-- 该属性是否必填 -->
<required>true</required>
<rtexprvalue>true</rtexprvalue>
<type>boolean</type>
</attribute>
</tag>
4:运行该标签
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%@ taglib uri="/Liuyujian2" prefix="L" %>
<!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>Insert title here</title>
</head>
<body>
<L:set var="name" value="qudamazi"></L:set>
--------------------------
<L:out value="${name}"></L:out>
<L:demo test="zahnsan"></L:demo>
</body>
</html>
运行结果：
//-------------------------- qudamazi
输出结果显示图：
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