Analysis and use of the principle of JSP Standard Lab (JSTL) in Java Library
JSP Standard Tag Library (JSTL) is an expansion function used in the Java class library to simplify and strengthen the development of JSP pages.JSTL provides a set of labels that can process data, control processes, perform cycle and conditional judgment through these labels.This article will introduce the principle analysis and use guidelines of JSTL, and provide relevant Java code examples.
Analysis of the principle of JSTL:
JSTL is implemented based on the model of label and label processor.Its label is defined in XML format and is used to introduce various functions in the JSP page, such as cycle, conditional judgment, formatting output, etc.The label processor is responsible for parsing and executing these labels.
The steps of using JSTL are as follows:
1. Import the label library of JSTL: Before using JSTL tags in the JSP page, you need to import the corresponding label library.Generally, the core functions and formatting functions can be introduced through the two label libraries of JSTL "Core" and "FMT".The method of importing the label library can use `<%@ taglib uri =" http://java.sun.com/jsp/jstl/core "prefix =" c "%>` and `<%@ taglib uri =" http://java.sun.com/jsp/jstl/fmt "prefix =" fmt " %>` `` `` `` `` `` `` `` `` `` `
2. Use JSTL tags: After importing the label library, you can use the label provided by JSTL on the JSP page.For example, `<C: Foreach>` tags can be used to recycling the collection and processing the elements in the set one by one; `<C: if>` tags can be used for conditional judgment, controlled according to the results of the conditions to control the page of the pageShow and hide.
3. Configure JSTL label processor: In order to enable the JSP container to correctly analyze and execute the JSTL label, configured in the deployment description file (such as web.xml) of the web application.You can register the JSTL label processor by adding the following configuration code:
<taglib>
<taglib-uri>http://java.sun.com/jstl/core</taglib-uri>
<taglib-location>/WEB-INF/c.tld</taglib-location>
</taglib>
Note that the path in the element of `taglib-logation>` is to point the definition file (.tld) of the JSTL label library.
Example of using JSTL:
The following is an example of using the JSTL cycle tag. This example is used to traverse a collection and output element:
jsp
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE html>
<html>
<head>
<title>JSTL Example</title>
</head>
<body>
<c:forEach var="item" items="${items}">
<p>${item}</p>
</c:forEach>
</body>
</html>
In the above examples, `<C: FOREACH>` Labels are used to circulate a collection named `Items`, and store each element in the set in a variable named` item`.`$ {item}` is used to output the value of the current element.
Summarize:
JSP Standard Tag Library (JSTL) is a Java class library for simplifying and strengthening the development of JSP pages.It uses the model of label and label processor to implement the expansion function, which can handle common logical operations such as data, control processes, cycle and conditional judgment.By importing JSTL label libraries, using JSTL labels, and configured JSTL label processors, the function of JSTL can be used flexibly on the JSP page.
