JSP標準標記庫（JSTL）教學

在JSP標準標記庫（JSTL）是很有用的JSP標簽的集合，它封裝常見的許多JSP應用程序的核心功能。

JSTL具有如迭代和條件，標簽為操縱XML文檔，國際化標簽，和SQL標簽常見，結構任務的支持。它還提供了集成現有的自定義標簽與JSTL標記框架。

JSTL標記可以進行分類，根據其功能，進入下麵可以創建一個JSP頁麵時，可以使用JSTL標簽庫組：

安裝JSTL庫：

如果您使用的是Apache Tomcat容器，那麼按照下麵兩個簡單的步驟：

從Apache標準標簽庫下載二進製分發和解壓的壓縮文件。
若要從Jakarta Taglibs中使用的標準標簽庫，隻需在分布的'lib'目錄複製JAR文件到您的應用程序的webappsROOTWEB-INFlib目錄中。

使用任何庫，必須包括<taglib>指令在每個JSP中使用該庫的頂部。

標簽的核心小組是最常用的JSTL標記。以下是語法包括JSTL core庫在JSP：

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

有以下核心JSTL標簽：

標簽	描述
<c:out >	Like <%= ... >, but for expressions.
<c:set >	Sets the result of an expression evaluation in a 'scope'
<c:remove >	Removes a scoped variable (from a particular scope, if specified).
<c:catch>	Catches any Throwable that occurs in its body and optionally exposes it.
<c:if>	Simple conditional tag which evalutes its body if the supplied condition is true.
<c:choose>	Simple conditional tag that establishes a context for mutually exclusive conditional operations, marked by <when> and <otherwise>
<c:when>	Subtag of <choose> that includes its body if its condition evalutes to 'true'.
<c:otherwise >	Subtag of <choose> that follows <when> tags and runs only if all of the prior conditions evaluated to 'false'.
<c:import>	Retrieves an absolute or relative URL and exposes its contents to either the page, a String in 'var', or a Reader in 'varReader'.
<c:forEach >	The basic iteration tag, accepting many different collection types and supporting subsetting and other functionality .
<c:forTokens>	Iterates over tokens, separated by the supplied delimeters.
<c:param>	Adds a parameter to a containing 'import' tag's URL.
<c:redirect >	Redirects to a new URL.
<c:url>	Creates a URL with optional query parameters

在JSTL格式標簽用於格式化和國際化的網站顯示文本，日期，時間和數字。以下是語法，包括格式化庫在JSP：

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

以下是格式化的JSTL標簽的列表：

標簽	描述
<fmt:formatNumber>	To render numerical value with specific precision or format.
<fmt:parseNumber>	Parses the string representation of a number, currency, or percentage.
<fmt:formatDate>	Formats a date and/or time using the supplied styles and pattern
<fmt:parseDate>	Parses the string representation of a date and/or time
<fmt:bundle>	Loads a resource bundle to be used by its tag body.
<fmt:setLocale>	Stores the given locale in the locale configuration variable.
<fmt:setBundle>	Loads a resource bundle and stores it in the named scoped variable or the bundle configuration variable.
<fmt:timeZone>	Specifies the time zone for any time formatting or parsing actions nested in its body.
<fmt:setTimeZone>	Stores the given time zone in the time zone configuration variable
<fmt:message>	To display an internationalized message.
<fmt:requestEncoding>	Sets the request character encoding

JSTL的SQL標記庫提供標簽為關係型數據庫（RDBMS），如Oracle，MySQL等，或Microsoft SQL Server進行交互。

以下是語法包括JSTL SQL庫在JSP：

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

以下是SQL JSTL標簽的列表：

標簽	描述
<sql:setDataSource>	Creates a simple DataSource suitable only for prototyping
<sql:query>	Executes the SQL query defined in its body or through the sql attribute.
<sql:update>	Executes the SQL update defined in its body or through the sql attribute.
<sql:param>	Sets a parameter in an SQL statement to the specified value.
<sql:dateParam>	Sets a parameter in an SQL statement to the specified java.util.Date value.
<sql:transaction >	Provides nested database action elements with a shared Connection, set up to execute all statements as one transaction.

JSTL的XML標記提供了創建和操作XML文檔的JSP為中心的方式。以下是語法包括JSTL的XML庫在JSP。

JSTL的XML標記庫有自定義標簽用於處理XML數據進行交互。這包括解析XML，轉換XML數據，流程和基於XPath表達式控製。

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

在繼續之前的例子，你需要下麵的兩個XML和XPath相關的庫文件複製到您的<Tomcat安裝目錄> lib中：

以下是XML的JSTL標簽列表：

標簽	描述
<x:out>	Like <%= ... >, but for XPath expressions.
<x:parse>	Use to parse XML data specified either via an attribute or in the tag body.
<x:set >	Sets a variable to the value of an XPath expression.
<x:if >	Evaluates a test XPath expression and if it is true, it processes its body. If the test condition is false, the body is ignored.
<x:forEach>	To loop over nodes in an XML document.
<x:choose>	Simple conditional tag that establishes a context for mutually exclusive conditional operations, marked by <when> and <otherwise>
<x:when >	Subtag of <choose> that includes its body if its expression evalutes to 'true'
<x:otherwise >	Subtag of <choose> that follows <when> tags and runs only if all of the prior conditions evaluated to 'false'
<x:transform >	Applies an XSL transformation on a XML document
<x:param >	Use along with the transform tag to set a parameter in the XSLT stylesheet

JSTL包含了一些標準函數，其中大部分是常用的字符串操作函數。以下是語法包括JSTL函數庫在JSP：

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

下麵是JSTL函數的列表：

Function	描述
fn:contains()	Tests if an input string contains the specified substring.
fn:containsIgnoreCase()	Tests if an input string contains the specified substring in a case insensitive way.
fn:endsWith()	Tests if an input string ends with the specified suffix.
fn:escapeXml()	Escapes characters that could be interpreted as XML markup.
fn:indexOf()	Returns the index withing a string of the first occurrence of a specified substring.
fn:join()	Joins all elements of an array into a string.
fn:length()	Returns the number of items in a collection, or the number of characters in a string.
fn:replace()	Returns a string resulting from replacing in an input string all occurrences with a given string.
fn:split()	Splits a string into an array of substrings.
fn:startsWith()	Tests if an input string starts with the specified prefix.
fn:substring()	Returns a subset of a string.
fn:substringAfter()	Returns a subset of a string following a specific substring.
fn:substringBefore()	Returns a subset of a string before a specific substring.
fn:toLowerCase()	Converts all of the characters of a string to lower case.
fn:toUpperCase()	Converts all of the characters of a string to upper case.
fn:trim()	Removes white spaces from both ends of a string.