The design principles and use of JSP Standard Tag Library (JSTL) in the Java class library

Java Standard Tag Library (JSTL) is a standard label library for simplifying the development of JSP pages.It provides a set of labels to process logic, display data, and management control processes, enabling developers to develop dynamic web applications more easily. The design principle of JSTL is to promote the separation of MVC (Model-View-Controller).It extracts the logical code in the JSP page to make the page clearer and easy to maintain.JSTL's design is inspired by JSP's custom tags, but compared to it, it is more concise and easy to use. JSTL provides five major label libraries: 1. Core tag library: The label library provides basic functions such as conditional judgment, iteration, variable management, and URL processing.For example, you can use the <C: If> tag for conditional judgment, <C: Foreach> tags to iterate, <C: Set> tags to set the value of the variable, and use the <C: URL> tag to process URL. 2. Formatal label library: The label library provides the formatting function of the date, numbers and messages.For example, you can use the <fMT: Formatdate> tag to format the date, <FMT: Formatnumber> tags to format numbers, <fmt: Message> tags to get multi -language messages. 3. SQL tag library: The label library provides the function of performing SQL query.You can use the <SQL: SetDataSource> tag to set the data source, <SQL: Query> tags to execute the query, <SQL: Transaction> tags to handle transactions. 4. XML tag library: The label library provides the ability to process XML data.You can use <x: Parse> tags to resolve XML files, <x: OUT> tags to display XML data, <x: Foreach> tags to iterate XML nodes, etc. 5. Function tag library: This label library provides some commonly used functions for string processing, date comparison and mathematical operations.You can use the <fn: specific> tag to obtain the length of the string, <fn: substring> tags to intercept the string, <fn: contains> tags to determine whether the strings contain a sub -string. The following is a simple example of using JSTL: First, import the JSTL label library at the top of the JSP page: jsp <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> Then use the <C: Foreach> label on the page to iterate a list: jsp <c:forEach items="${students}" var="student"> <p>${student.name}</p> </c:forEach> In the above code, `$ {Students}` is a list of students transmitted from the back end to the front end. In each iteration, you can use the `$ {student.name}` to get the student's name and display it on the page. By using the JSTL label library, developers can separate the page logic from displaying logic to make the code more concise and readable.It also provides rich labels and functions, which greatly improves the development efficiency of the JSP page. In summary, JSTL is a standard label library for simplifying the development of JSP pages. It provides a set of labels to process logic, display data, and management control processes.By separating the logic of page logic from display logic, the JSP page is clearer and easy to maintain.