JSTL Functions标签库提供的通用EL函数

在JSTL Functions标签库中提供了一组常用的EL函数，主要用于处理字符串，在JSP文件中可以直接使用这些函数。在JSP文件中使用Functions标签库，要先通过taglib指令引入该标签库：

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

Functions标签库中的16个EL函数：

函数描述fn:contains用于判断在源字符串中是否包含目标字符串fn:containsIgnoreCase用于判断在源字符串中是否包含目标字符串，判断时忽略大小写fn:startsWith判断源字符串是否以指定的目标字符串开头fn:endsWith判断源字符串是否以指定的目标字符串结尾fn:indexOf在源字符串中查找目标字符串，并返回源字符串中最先与目标字符串匹配的第一个字符的索引，如果源字符串中不包含目标字符串，则返回-1fn:replace把源字符串中的一部分字符串替换为另外的字符串，并返回替换后的字符串fn:substring用于获取源字符串中的特定子字符串fn:substringBefore用于获取源字符串中的指定子字符串之前的子字符串fn:substringAfter用于获取源字符串中的指定子字符串之后的子字符串fn:split用于将源字符串拆分为一个字符串数组fn:join用于将源字符串数组中的所有字符串连接为一个字符串fn:toLowerCase用于将源字符串中的所有字符改为小写fn:toUpperCase用于将源字符串中的所有字符改为大写fn:trim用于将源字符串中的开头和末尾的空格删除fn:escapeXml用于将源字符串中的字符<,>,"和&等转换为转义字符fn:length用于返回字符串中的字符的个数，或者集合和数组中的元素的个数顺便附上standard.jar下的META-INF下的fn.tld源文件

<?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>JSTL 1.1 functions library</description>  <display-name>JSTL functions</display-name>  <tlib-version>1.1</tlib-version>  <short-name>fn</short-name>  <uri>http://java.sun.com/jsp/jstl/functions</uri>  <function>    <description>      Tests if an input string contains the specified substring.    </description>    <name>contains</name>    <function-class>org.apache.taglibs.standard.functions.Functions</function-class>    <function-signature>boolean contains(java.lang.String, java.lang.String)</function-signature>    <example>      <c:if test="${fn:contains(name, searchString)}">    </example>  </function>  <function>    <description>      Tests if an input string contains the specified substring in a case insensitive way.    </description>    <name>containsIgnoreCase</name>    <function-class>org.apache.taglibs.standard.functions.Functions</function-class>    <function-signature>boolean containsIgnoreCase(java.lang.String, java.lang.String)</function-signature>    <example>      <c:if test="${fn:containsIgnoreCase(name, searchString)}">    </example>  </function>  <function>    <description>      Tests if an input string ends with the specified suffix.    </description>    <name>endsWith</name>    <function-class>org.apache.taglibs.standard.functions.Functions</function-class>    <function-signature>boolean endsWith(java.lang.String, java.lang.String)</function-signature>    <example>      <c:if test="${fn:endsWith(filename, ".txt")}">    </example>  </function>  <function>    <description>      Escapes characters that could be interpreted as XML markup.    </description>    <name>escapeXml</name>    <function-class>org.apache.taglibs.standard.functions.Functions</function-class>    <function-signature>java.lang.String escapeXml(java.lang.String)</function-signature>    <example>      ${fn:escapeXml(param:info)}    </example>  </function>  <function>    <description>      Returns the index withing a string of the first occurrence of a specified substring.    </description>    <name>indexOf</name>    <function-class>org.apache.taglibs.standard.functions.Functions</function-class>    <function-signature>int indexOf(java.lang.String, java.lang.String)</function-signature>    <example>      ${fn:indexOf(name, "-")}    </example>  </function>  <function>    <description>      Joins all elements of an array into a string.    </description>    <name>join</name>    <function-class>org.apache.taglibs.standard.functions.Functions</function-class>    <function-signature>java.lang.String join(java.lang.String[], java.lang.String)</function-signature>    <example>      ${fn:join(array, ";")}    </example>  </function>  <function>    <description>      Returns the number of items in a collection, or the number of characters in a string.    </description>    <name>length</name>    <function-class>org.apache.taglibs.standard.functions.Functions</function-class>    <function-signature>int length(java.lang.Object)</function-signature>    <example>      You have ${fn:length(shoppingCart.products)} in your shopping cart.    </example>  </function>  <function>    <description>      Returns a string resulting from replacing in an input string all occurrences      of a "before" string into an "after" substring.    </description>    <name>replace</name>    <function-class>org.apache.taglibs.standard.functions.Functions</function-class>    <function-signature>java.lang.String replace(java.lang.String, java.lang.String, java.lang.String)</function-signature>    <example>      ${fn:replace(text, "-", "•")}    </example>  </function>  <function>    <description>      Splits a string into an array of substrings.    </description>    <name>split</name>    <function-class>org.apache.taglibs.standard.functions.Functions</function-class>    <function-signature>java.lang.String[] split(java.lang.String, java.lang.String)</function-signature>    <example>      ${fn:split(customerNames, ";")}    </example>  </function>  <function>    <description>      Tests if an input string starts with the specified prefix.    </description>    <name>startsWith</name>    <function-class>org.apache.taglibs.standard.functions.Functions</function-class>    <function-signature>boolean startsWith(java.lang.String, java.lang.String)</function-signature>    <example>      <c:if test="${fn:startsWith(product.id, "100-")}">    </example>  </function>  <function>    <description>      Returns a subset of a string.    </description>    <name>substring</name>    <function-class>org.apache.taglibs.standard.functions.Functions</function-class>    <function-signature>java.lang.String substring(java.lang.String, int, int)</function-signature>    <example>      P.O. Box: ${fn:substring(zip, 6, -1)}    </example>  </function>  <function>    <description>      Returns a subset of a string following a specific substring.    </description>    <name>substringAfter</name>    <function-class>org.apache.taglibs.standard.functions.Functions</function-class>    <function-signature>java.lang.String substringAfter(java.lang.String, java.lang.String)</function-signature>    <example>      P.O. Box: ${fn:substringAfter(zip, "-")}    </example>  </function>  <function>    <description>      Returns a subset of a string before a specific substring.    </description>    <name>substringBefore</name>    <function-class>org.apache.taglibs.standard.functions.Functions</function-class>    <function-signature>java.lang.String substringBefore(java.lang.String, java.lang.String)</function-signature>    <example>      Zip (without P.O. Box): ${fn:substringBefore(zip, "-")}    </example>  </function>  <function>    <description>      Converts all of the characters of a string to lower case.    </description>    <name>toLowerCase</name>    <function-class>org.apache.taglibs.standard.functions.Functions</function-class>    <function-signature>java.lang.String toLowerCase(java.lang.String)</function-signature>    <example>      Product name: ${fn.toLowerCase(product.name)}    </example>  </function>  <function>    <description>      Converts all of the characters of a string to upper case.    </description>    <name>toUpperCase</name>    <function-class>org.apache.taglibs.standard.functions.Functions</function-class>    <function-signature>java.lang.String toUpperCase(java.lang.String)</function-signature>    <example>      Product name: ${fn.UpperCase(product.name)}    </example>  </function>  <function>    <description>      Removes white spaces from both ends of a string.    </description>    <name>trim</name>    <function-class>org.apache.taglibs.standard.functions.Functions</function-class>    <function-signature>java.lang.String trim(java.lang.String)</function-signature>    <example>      Name: ${fn.trim(name)}    </example>    </function></taglib>