In-depth analysis of the technical principles of the Jakarta Expression Language API framework (IN-Depth Analysis of the Technical Principles of Jakarta Expression Language In Java Cl Ass Libraries)

In -depth analysis of the technical principles of Jakarta Expression Language API frame Overview: Jakarta Expression Language (EL), that is, Jakarta's expression language, plays an important role in Java's enterprise -level application development.It is part of the specification of the JavaserVer Pages (JSP) and is widely used for dynamic web development.This article will discuss the technical principles of the Jakarta Expression Language API framework, focusing on its working principles, core concepts and main usage. 1. Overview of Jakarta Exposition Language API framework Jakarta Expression Language API framework is a Java class library used to analyze and calculate expressions.It provides a simple and powerful way to use expression language to dynamically evaluate and operate Java objects.The core idea of the framework is to separate the expression from the data model to improve the maintenance and flexibility of the application. 2. Working principle Jakarta Expression Language API can be divided into the following steps: 1. Analysis: Use an expression language parser to convert the expression string into an abstract syntax tree (AST) for form.AST is a tree -shaped structure that is used to represent the relationship between each part of the expression and them. 2. Compile: compile AST as Java bytecode to facilitate the analysis and calculation of expressions during runtime.This can greatly improve the execution efficiency of expression. 3. Evaluation: Based on the data model, the compiled expressions are evaluated and returned to the results.Since the compilation process is only executed once, it can get higher performance when evaluating the same expression many times. 3. Core concept 1. Expression: It consists of variables, computing symbols, and functions for calculating values.The expression can be a simple variable reference, or a complex arithmetic operation and logical operation. 2. Variable: The data used in the expression.Variables can be a basic type, object type or collection type. 3. Concope: Symbols used to operate and merge variables.Common operators include arithmetic operators, relationship operators, and logical operators. 4. Function: Provide a set of predefined operations that can be called in the expression.The function accepts zero or multiple parameters and returns a value. Fourth, the main usage Jakarta Expression Language API framework has a wide range of application scenarios. The following are some of the main usage: 1. Dynamic web development: Use EL expressions in the JSP page to dynamically render the content of the page, and automatically update the page display according to the change of the data model. 2. Configuration file analysis: Use EL expressions to replace the parameter values in the configuration file to actual data to improve the flexibility and maintenance of the configuration file. 3. Data verification and filtration: The data entered by the user can be verified and filtered through the EL expression to ensure the effectiveness and security of the data. 4. Rules engine: EL expression can be used as part of the regular engine, which is used to define and calculate rules and movements. Example code: import javax.el.ExpressionFactory; import javax.el.Expression; import javax.el.ELContext; import javax.el.BeanELResolver; public class JakartaExpressionLanguageExample { public static void main(String[] args) { // Create an expression factory ExpressionFactory factory = ExpressionFactory.newInstance(); // Create EL context ELContext context = new ELContext(); // Set the variables of EL context context.getVariableMapper().setVariable("name", factory.createValueExpression("John Doe", String.class)); // Create an expression Expression expression = factory.createExpression("${name}"); // Evaluate expression and output results System.out.println(expression.getValue(context)); } } in conclusion: Jakarta Expression Language API framework is a powerful and flexible tool that can be used to process and calculate expression.This article introduces the working principle, core concept and main usage of the framework. I hope to help readers better understand and apply the technical principles of Jakarta Expression Language API framework in the Java library.Through reasonable use of this framework, developers can improve the readability, flexibility and efficiency of the code, thereby speeding up the speed and quality of application development.