For details, the technical principles of the Jakarta Expression Language API framework in the Java library s libraries)

The Jakarta Expression Language (Jexl) API framework in the Java class library is an expression language analysis and execution engine for dynamic computing and processing expressions in Java applications.The Jexl API provides a simple and flexible way to analyze and execute expressions. These expressions can include variables, function calls, operators, and control streams, and then provide a ability to expand the Java language. The technical principles of the JEXL framework are mainly based on the following aspects: 1. Parser: The Jexl framework first analyzes the input expression for syntax to convert it into an abstract syntax tree (AST).AST is a tree -like structure that organizes and represents each component, operating symbols and control flow structures, and the relationship between them. 2. Semantic Analysis: During the semantic analysis stage, the JEXL framework traverses and analyzes abstract syntax trees, and is checked and analyzed for variables and functions to ensure that they are legal and accessible in the scope of action.In addition, semantic analysis also includes operations such as data type inspection, type conversion, and automatic boxing/box dismantling. 3. Code Generation and Execution: When the abstract syntax tree is completely established and verified, the JEXL framework will perform the engine generation target code for calculating and executing expressions.This code can be dynamically compiled and loaded at runtime to improve the performance of expression execution.The JEXL framework also provides support for control flows, such as if-Artse, FOR, While), abnormal treatment, etc. 4. Context Management: During the process of expression calculation, the Jexl framework needs to access and operate variables, functions, etc. context environments.Therefore, it provides the function of managing the context environment, which can bind variables to specific objects or values for use in expressions. The following is a simple example code, which demonstrates the use of the Jexl framework: import org.apache.commons.jexl3.*; public class JexlExample { public static void main(String[] args) { // Create a JEXL engine JexlEngine jexlEngine = new JexlBuilder().create(); // Create an expression String expression = "a + b"; // Create the context environment JexlContext context = new MapContext(); context.set("a", 5); context.set("b", 10); // Analysis and execution expression JexlExpression jexlExpression = jexlEngine.createExpression(expression); Object result = jexlExpression.evaluate(context); System.out.println ("Result:" + Result); // Output results: 15 } } In the above code, we first created a Jexl engine and then defined a simple expression "A + B".Then, we created a context environment and tied the variables "a" and "b" to the value 5 and 10, respectively.Finally, we use the JEXL engine to analyze and execute expressions and output the calculation results. In short, the Jakarta Expression Language (Jexl) API framework is a powerful expression analysis and execution engine that can achieve dynamic expression computing and processing in Java applications.Its technical principles mainly involve grammar analysis, semantic analysis, code generation and execution, and context environmental management.By flexibly using the Jexl framework, developers can enhance the flexibility and scalability of the Java language and achieve more dynamic and intelligent applications.