Jakarta Standard Tag Library API Advanced Utilities (Advanced USAGE TIPS)

Jakarta Standard Tag Library (JSTL) is a Java standard library for performing universal tasks on the JSP page.JSTL provides a set of labels to handle common page development tasks such as cycles, conditional statements, formatting output, and internationalization.In addition to JSP tags, JSTL also provides a set of core labels, formatted tags, function tags and XML tags. In this article, we will thoroughly study the advanced use skills of JSTL, including how to use core labels, how to customize function tags, and how to use XML tags for data processing. 1. Flexible use of the core label: The core label library of JSTL provides a set of powerful labels that can process variables, process control and sets in the JSP page.Here are some advanced skills: a) `<C: if>` and `<C: Choose>` Tags: These tags allow us to execute the specified code block according to the conditions.You can use `<C: if>` tags to determine a single condition, and `<C: Choose>` tags can be used to choose from multiple conditions. <c:if test="${condition}"> <!-- code block to be executed if condition is true --> </c:if> <c:choose> <c:when test="${condition1}"> <!-- code block to be executed if condition1 is true --> </c:when> <c:when test="${condition2}"> <!-- code block to be executed if condition2 is true --> </c:when> <c:otherwise> <!-- code block to be executed if all conditions are false --> </c:otherwise> </c:choose> b) `<C: Foreach>` Tags: This tag can be used to traverse the collection and execute the specified code block at each iteration. <c:forEach items="${collection}" var="item"> <!-- code block to be executed for each item in the collection --> </c:forEach> 2. Custom function tag: JSTL also provides a function label library that allows us to customize and use functions on the JSP page.This function is particularly suitable for performing some commonly used data processing operations on the page.The following is an example: a) Create the mark file of the custom function tag library (.tld): <taglib xmlns="http://java.sun.com/xml/ns/j2ee" version="2.1"> <tlib-version>1.0</tlib-version> <short-name>myfunctions</short-name> <uri>http://example.com/myfunctions</uri> <function> <name>customFunction</name> <function-class>com.example.MyFunctions</function-class> <function-signature>java.lang.String customFunction(java.lang.String)</function-signature> </function> </taglib> b) Java class to create a custom function: package com.example; public class MyFunctions { public static String customFunction(String input) { // custom logic to process input and return a result } } c) Use a custom function on the JSP page: <%@ taglib uri="http://example.com/myfunctions" prefix="myfn" %> ${myfn:customFunction('input')} 3. Use XML tag for data processing: JSTL also provides a set of XML tags to analyze and process XML data.These tags are very useful when processing XML documents.The following is an example: a) Analyze the XML document and get the elemental value: <%@ taglib uri="http://java.sun.com/jsp/jstl/xml" prefix="xml" %> <xml:parse var="xmlDoc" scope="request" xml="${xmlString}" /> <%-- Accessing element values --%> <xml:forEach select="$xmlDoc/root/element" var="element"> Value: <xml:out select="$element" /> </xml:forEach> b) Select a specific XML element according to the path: <%@ taglib uri="http://java.sun.com/jsp/jstl/xml" prefix="xml" %> <xml:parse var="xmlDoc" scope="request" xml="${xmlString}" /> <%-- Selecting specific elements --%> <xml:forEach select="$xmlDoc/root/element[condition='value']" var="element"> <!-- code block to be executed for each selected element --> </xml:forEach> In this article, we introduced some senior use skills of JSTL.By flexibly using core labels, custom function tags, and XML tags, we can better handle common tasks and data in the JSP page.These techniques will help us write clearer and more maintainable JSP code and improve page development efficiency.