The principle of JSP Standard Tag Library (JSSTL) and the response in the Java class library

The principle of JSP Standard Tag Library (JSSTL) and applications in the Java class library The JSP Standard Tag Library (JSTL) is a Java standard formulated by the Java Community Process (JCP) for functions of common logic and control flow on the JSP page.JSTL provides a set of custom labels that can be used in the JSP page to simplify the work of developers. The working principle of JSTL is to be achieved by converting the custom label into the corresponding Java code.These labels are compiled to Java bytecode and are then loaded and executed by Web containers.Jstl translates it into an equivalent Java code by parsing the label on the page, and then performs the corresponding features.This process occurs during page rendering and can dynamically generate HTML output. JSTL provides multiple label libraries, including core (Core) label library, formatting (FMT) label library, XML (XML) tag library and SQL (SQL) tag library.The core label library provides functions such as control flow, iterative, conditional judgment, and variable settings.The formatting label library provides localization and formatting functions of date, digital, currency and message.The XML label library is used to process XML data.The SQL label library is used to perform SQL query and operating database. Here are some examples of JSTL in the Java library: 1. Use the Foreach label of the core label library to cycle: <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> <c:forEach items="${items}" var="item"> <p>${item}</p> </c:forEach> This code will circulate a collection of each element called `Items` on the page. 2. Use the FMT: Message label for the formatting tag library for international message processing: <%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt" %> <fmt:setBundle basename="com.example.messages" var="msg" /> <fmt:message key="welcome.message" bundle="${msg}" /> This code uses the `FMT: Message` label from a resource file to get a message called` Welcome.Message` and output them to the page. The application of JSTL can greatly simplify the development of the JSP page, enabling developers to focus more on business logic rather than the underlying grammar and control flow.At the same time, the modular design of the JSTL label library allows developers to choose different functional modules according to their needs, which improves the maintenance and scalability of the code. It should be noted that in order to use the JSTL label library on the JSP page, you need to add the corresponding label library declaration to the head of the page and introduce JSTL related library files in the dependency configuration of the project. It is hoped that this article will help understand the principle of understanding the JSP standard label library (JSTL) and the application in the Java class library.