Jakarta Standard Tag Library API in the Java Class Library (In-Depth Analysis of Jakarta Standard Tag Library ap
Detailed explanation
Overview:
Jakarta Standard Tag Library (JSTL) is a standard label library for Java Web application development. Through this library, it can simplify the code in the JSP page and provide modular implementation of common functions.The JSTL API provides some labels that can be used in the JSP page to handle common tasks such as cycling, conditional judgment, and formatting output.This article will in -depth analysis of the use of JSTL API and provide some related Java code examples.
Import of JSTL tag library:
To use the JSTL API on the JSP page, you need to introduce the corresponding label library first.Add the following code to the head tags on the JSP page to import the core label library of JSTL:
jsp
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
Common labels of JSTL core label library:
1. C: IF -Condition judgment tag
jsp
<c:if test="${condition}">
<!-In this label, you can place content to be executed->
</c:if>
2. C: FOREACH -Cycling iteration label
jsp
<c:forEach items="${collection}" var="item" varStatus="status">
<!-In this label, you can place the content to be executed. ITEM variables represent the current cycle, and the STATUS variable represents iterative status->
</c:forEach>
3. C: Choose -Multiple Conditions Select Tags
jsp
<c:choose>
<c:when test="${condition1}">
<! --- Elimination of the content of 1 time-->
</c:when>
<c:when test="${condition2}">
<! --- Elimination of the content at 2 o'clock->
</c:when>
<c:otherwise>
<!-What is executed in other cases->
</c:otherwise>
</c:choose>
4. C: SET -Set variable tag
jsp
<c:set var="variableName" value="${expression}" />
5. C: OUT -Output Tag
jsp
<c:out value="${expression}" />
Example of JSTL API:
Suppose there is a student list, each student has two attributes: name and Age.Below is an example using the JSTL API to show the function of students and judge whether the students are adults based on age:
jsp
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<Title> Student List </Title>
</head>
<body>
<H1> Student List </h1>
<c:forEach items="${students}" var="student" varStatus="status">
<p> Name: $ {Student.name} </p>
<p> Age: $ {Student.age} </p>
<c:choose>
<c:when test="${student.age >= 18}">
<p> Adult </p>
</c:when>
<c:otherwise>
<p> Minor </p>
</c:otherwise>
</c:choose>
<br>
</c:forEach>
</body>
</html>
In the above examples, we use the C: Foreach tags to traverse the student list, and use the C: Choose tag to determine whether the students' age is greater than or equal to 18.Through the core label library of JSTL, we can output the name, age, and adult status in the student list to the HTML page.
Summarize:
Through the Jakarta Standard Tag Library (JSTL) API, we can simplify the code in the JSP page to improve the readability and maintenance of the code.This article provides a detailed introduction and use example of JSTL API, hoping to help readers better understand and apply JSTL API.In actual development, we can use more functions provided by the JSTL label library as needed to reduce the writing of duplicate code and develop the Java Web application more efficiently.
