Jakarta Expression Language API framework Frequently Asked Questions Answers
Jakarta Expression Language API framework Frequently Asked Questions Answers
introduce:
JavaseerVer Pages (JSP) technology is a common technology in the development of Java enterprise applications, and Jakarta Expression Language (EL) API is an important part of JSP technology.This article will list the common questions in the Jakarta El API framework and provide corresponding answers and Java code examples.
Question 1: What is Jakarta Expression Language API?How to use it in the project?
answer:
Jakarta Expression Language (EL) API is a language used to access the server on the server on the JSP page and label library.It provides a simplified way to access and operate the attributes and methods of the Java object.To use the Jakarta El API in the project, you need to add related dependencies to the project's classpath.Below is a sample pom.xml file configuration of a Maven project:
<dependency>
<groupId>jakarta.el</groupId>
<artifactId>jakarta.el-api</artifactId>
<version>3.0.3</version>
</dependency>
Question 2: How to use the Jakarta El API on the JSP page?
answer:
It is very simple to use the Jakarta El API on the JSP page.You can use `$ {}` to access the attributes or methods of the Java object on the server.The following is an example:
jsp
<%@ page language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<title>JSP Example</title>
</head>
<body>
<c:set var="name" value="John" />
<h1>Welcome, ${name}</h1>
</body>
</html>
In the above example, the expression of `$ {name}` will be replaced with the value of the variable `name` and finally output to the page.
Question 3: How to use conditions and cycle sentences on the JSP page?
answer:
Jakarta El API provides simplified conditions and how to use circular statements.You can use `<C: if>` and `<C: Foreach>` to implement conditional judgment and circulation.The following is an example:
jsp
<%@ page language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<title>JSP Example</title>
</head>
<body>
<c:set var="count" value="5" />
<c:if test="${count > 0}">
<ul>
<c:forEach begin="1" end="${count}" var="i">
<li>Item ${i}</li>
</c:forEach>
</ul>
</c:if>
<c:if test="${count <= 0}">
<p>No items to display.</p>
</c:if>
</body>
</html>
In the above example, if the value of the variable `count` is greater than 0, a list will be displayed, and the list contains items from 1 to` Count`.Otherwise, a message will be displayed "No its to display.".
Question 4: How to use EL expression to call the Java method?
answer:
You can use the JAKARTA EL API to call the Java object through EL expression.Method call uses the `.` operator to carry parameters.The following is an example:
jsp
<%@ page language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<title>JSP Example</title>
</head>
<body>
<%
// Create a CALCULATOR class in the Java code
// There is an ADD method in the Calculator class, which is used to add two numbers
class Calculator {
public int add(int a, int b) {
return a + b;
}
}
// Use EL expressions to call Calculator class ADD method in the JSP page
Calculator calculator = new Calculator();
int result = (Integer) pageContext.getAttribute("calculator.add(2, 3)");
%>
<p>Result: ${result}</p>
</body>
</html>
In the above example, we created a CALCULATOR class in the Java code, and used EL expressions to call the ADD method in the JSP page.
These are answers and examples code for some common questions in the Jakarta Exposition Language API framework.I hope to help you use Jakarta El API for JSP development!
