The technical principles of the Java class library based on the Jakarta Expression Language API framework S)

Discussion on the technical principles of Jakarta Exposition Language (Jexl) API framework introduce Jakarta Expression Language (Jexl) API in the Java Class Library can help developers implement dynamic calculations through simple expression analysis and evaluation.This article will explore the technical principles of the Jexl API and provide some Java code examples to illustrate its usage. What is Jakarta Exposition Language (Jexl) API? Jexl is an open source Java expression language framework and part of the Jakarta Commons project.It provides a simple way for Java developers to analyze and evaluate dynamic expressions, thereby achieving more flexible computing power.The core function of the Jexl API is to analyze the expression string into an executable code and provide a context environment to evaluate these code. Jexl API's technical principle The technical principle of Jexl API is based on the working principle of parser and assessor. 1. parser (Parser): Jexl parser is responsible for parsing the input expression string into an abstract syntax tree (AST).This process includes two stages: phrase analysis and grammar analysis. -Lexical Analysis: The parser first marked the input expression string and split it into a lexeme.The phrase analyzer converts the expression string into multiple phrase marks (token) according to the pre -defined lexical rules. -Syntax Analysis: The parser combines the lexical marking into a grammar tree according to the grammar rules defined in advance.This grammar tree represents the layered structure of the expression, which determines the relationship between the priority and the number of operations of the operator. 2. Evaluator: Once the construction of the abstract syntax tree is completed, the Jexl evaluation device will traverse the syntax tree and evaluate it based on the type and value of the node.The assessor uses variables and methods provided by the context environment to process each node and returns the result. -Context: Jexl provides a context environment for evaluations to use when parsing and evaluating expressions.Developers can define and set variables, methods and constants in the context environment.This allows the reference and use these context elements in the expression. -In abnormal processing: During the assessment process, if the non -supported operators, unfarished variables or methods are encountered, the Jexl assessor will throw out the corresponding abnormalities, and developers can capture and deal with these abnormalities. Java code example Here are several examples of Java code using Jexl API: 1. Analysis and evaluation expression: import org.apache.commons.jexl3.*; public class JexlExample { public static void main(String[] args) { JexlEngine jexl = new JexlBuilder().create(); JexlExpression expression = jexl.createExpression("2 + 3 * 4"); JexlContext context = new MapContext(); Object result = expression.evaluate(context); System.out.println (result); // Output: 14 } } 2. Use the context variable: import org.apache.commons.jexl3.*; public class JexlExample { public static void main(String[] args) { JexlEngine jexl = new JexlBuilder().create(); JexlExpression expression = jexl.createExpression("count * 10"); JexlContext context = new MapContext(); context.set("count", 5); Object result = expression.evaluate(context); System.out.println (result); // Output: 50 } } in conclusion Jakarta Expression Language (Jexl) API provides a flexible and powerful way to analyze and evaluate dynamic expressions.By using the Jexl API, developers can implement more advanced computing functions in Java.Through the discussion of this article, we understand the working principle of the Jexl API and provide some code examples to illustrate its use method.I hope these knowledge can help you better understand and apply the Jexl API.