Jakarta Expression Language API framework in the Java library analysis in the Java library

Jakarta Expression Language (EL) API framework is a powerful and flexible Java class library for expression and processing of expression in Java Web applications.This article will explore the technical principles of Jakarta Expression Language API framework in the Java class library and provide some Java code examples. 1. What is Jakarta Expression Language API? Jakarta Expression Language (EL) API is a standardized technology for processing expression for expression.It is part of the Jakarta EE specification, which aims to provide a unified way to handle expression in the Java Web application.EL API supports dynamically calculating and processing expressions during runtime, which greatly increases the flexibility and scalability of the application. 2. The working principle of Jakarta El API The core principle of Jakarta El API is based on analysis, computing and processing expression.It uses an Evaluator to analyze the expression and calculate the result when runtime.The following is the working principle of Jakarta El API: -Profotor analysis: First, the expression parser analyzes the input expression as a syntax tree, which is a layered tree structure of a representative expression structure. -Agenal tree evaluation: Then, the syntax tree traverses through the evaluation device, and the result of the expression of the expression according to specific semantic rules.The appraiser will perform the corresponding operations according to the type of expression and the context environment. -The result returns: Finally, the assessor calculates the result of the expression and return it to the call party.The caller can use the result as needed. 3. Jakarta El API example The following is a simple example of using the Jakarta El API, which shows how to calculate the expression in the Java Web application: import javax.el.*; public class Main { public static void main(String[] args) { // Create an EL expression engine ExpressionFactory factory = ExpressionFactory.newInstance(); // Create an EL context ELContext context = new ELContext() { // Todo: Implement the getContext method, return the context environment for expression operation }; // Define a expression String expressionString = "${2 + 3}"; // Analytical expression ValueExpression expression = factory.createValueExpression(context, expressionString, Object.class); // Calculate the result of the expression Object result = expression.getValue(context); // Print the result of the expression System.out.println ("The result of the expression is" + Result); } } In the above example, we first created an EL expression engine, and then created an EL context object through the `newInstance` method of the` ExpressionFactory` class.Next, we define a simple additional expression `$ {2 + 3}`. Then, we use the `CreateValueExpression` method to analyze the expression with the` ExpressionFactory`, and create an object of `ValueExPression.Finally, we call the `GetValue` method to calculate the results of the expression and print the results. Through the above examples, we can see that the Jakarta El API provides a simple and powerful way to calculate and process expressions.It can be used at all levels of the Java web application, including template engines, data verification, dynamic computing, etc., which greatly improves the scalability and flexibility of the application. Summarize: This article introduces the technical principles of Jakarta Expression Language (EL) API framework in the Java class library.We understand that the Jakarta El API is a standardized technology for processing expression for expression, and explains its working principle in detail through the steps of analysis, computing and processing expressions.At the same time, we provide a simple Java code example to demonstrate the use of Jakarta El API.It is believed that through the elaboration of this article, readers have a deeper understanding of the technical principles of Jakarta El API and can be flexibly used in practical applications.