Research On the Technical Principles of Jakarta Expression Language in Java Class Librases Cure
JAKARTA Expression Language API framework in the Java class library
Summary: Jakarta Expression Language (EL) API is a framework for vouual language for expression language in the Java program.This article will study the technical principles of the Jakarta El API framework, including its working principles, core characteristics, and example code.
preface:
With the extensive development and application of the Java language, the Jakarta El API framework in the Java class library has become an important tool for processing expression of expression in Java programs.The framework plays a key role in technologies such as JSP (JavaseerVer Pages) and JSF (Javaseerver Faces).This article will introduce the technical principles of the Jakarta El API to help readers understand the working principles and core characteristics of it.
Introduction
Jakarta Expression Language (referred to as Jakarta El) is a set of specifications used to videos in Java applications.It enables developers to calculate and operate text string at runtime, so as to realize the dynamic expression of dynamic expression.The Jakarta El API has the advantages of high performance, easy use and flexibility, so it is widely used in the Java class library.
Second, the working principle of Jakarta Exposition Language API
The working principle of Jakarta El API is based on a series of core components and interfaces.The following is the workflow of the Jakarta El API:
1. Grammar analysis: First of all, the Jakarta El API will analyze the input expression string to syntax and convert it into an abstract syntax tree (AST).This step is mainly completed by the phrase analyzer and grammar analyzer.
2. AST Construction: Through grammar analysis, the Jakarta El API will build an abstract syntax tree (AST), which represents the structure of input expression.
3. Variable analysis: The variables in the Jakarta El API parsing expression, and the value of the variable is used as an calculation input.
4. Computing Value: Based on the results of variable analysis, the value of the value on the AST to obtain the result of the final expression.
5. Results return: The final value of the value will be returned as the return value to the caller.
Third, the core characteristics of Jakarta Exposition Language API
The Jakarta El API provides a series of core features that make it more convenient to value the expression language in Java applications.The following are some of the core features of Jakarta El API:
1. Nested attribute access: Jakarta El API supports directly accessing the nested attribute through the point operator, such as obj1.obj2.property.
2. Method call: Jakarta El API allows the method to directly call the object in the expression and pass the parameters.
3. Collection and array access: Jakarta El API provides convenient grammar to access elements in the collection or array.
4. Combat support: Jakarta El API supports most common arithmetic, logic, relationships, and conditional operators.
5. Custom function: Developers can add custom functions by extending the Jakarta El API to meet specific needs.
Fourth, Jakarta Exposition Language API example code
Here are some examples of examples using Jakarta El API:
1. Nested attribute access:
ELProcessor elProcessor = new ELProcessor();
elProcessor.eval("obj1.obj2.property");
2. Method call:
ELProcessor elProcessor = new ELProcessor();
elProcessor.set("obj", new MyObject());
elProcessor.eval("obj.myMethod()");
3. Collection and array access:
ELProcessor elProcessor = new ELProcessor();
elProcessor.set("list", Arrays.asList("item1", "item2", "item3"));
String item = (String) elProcessor.eval("list[0]");
5. Custom function:
public class StringUtils {
public static String reverse(String str) {
return new StringBuilder(str).reverse().toString();
}
}
ELProcessor elProcessor = new ELProcessor();
elProcessor.defineFunction("StringUtils", "reverse", StringUtils.class.getMethod("reverse", String.class));
elProcessor.eval("StringUtils.reverse('hello')");
in conclusion:
This article deeply studies the technical principles of the Jakarta Expression Language API framework in the Java class library, including its working principles, core characteristics, and related example code.Through the study of the Jakarta El API, developers can better understand and use the framework of expression language to value value.
