Introduction to the technical principles of JBoss Reflection framework and Java class library

The Jboss Reflection framework is a reflex mechanism based on the Java language that can dynamically check, obtain and operate information at runtime.The Java class library also contains various reflection technologies. They can achieve some advanced functions through the reflection mechanism, such as dynamic loading classes, dynamic proxy and annotations. The reflection mechanism is a powerful tool provided by Java. It allows us to analyze the structure of the class during runtime, the member variables, methods and constructors of the obtained class, and even create objects and call methods dynamically at runtime.This ability is very useful in many practical application scenarios, such as framework development, ORM (object relationship mapping) framework and testing tools. In Java, each class will generate a bytecode file after the compilation is completed. This file contains the definition of metadata and methods of the class. The reflection technology is achieved by analyzing these bytecode files.In Java, the reflection is mainly implemented through the following core classes: Class, Field, Method, and Constructor. The Class class is the core class of reflection, which contains the structure and information of the descriptive class, such as Getname () to obtain the name of the class, getFields () to obtain a public member variable that can obtain a classwait.We can use Class classes to obtain class information, such as judging whether classes are abstract classes, parent -class interfaces that obtain classes, and obtained class interfaces. The Field class is used to describe a member variable, which contains the method of describing variable information, such as getname () to obtain the name of the variable, gettype () to obtain the type of variable, ISPUBLIC () can determine whether the variable is a public variable, etc.EssenceThrough the Field class, we can obtain a class member variable at runtime, and can operate it, such as obtaining the value of the variable, modifying the value of the variable, etc. The MetHod class is used to describe a class method, which also contains the method of description methods, such as the name of Getname () that can obtain the method, Getparametertypes () that can obtain the parameter type, getReTurntype () to obtain the return type of method, etc.EssenceThrough the METHOD class, we can obtain a class method at runtime and can call these methods. Constructor class is used to describe the constructor of the class, which contains methods to describe the constructor. For example, getParametertypes () can obtain parameter types of the constructor, ISVARARGS () can determine whether the constructor is a variable parameter.Through the Constructor class, we can obtain the constructor of the class at runtime, and we can use the constructor to create an object. The following is a simple example of using a reflection mechanism: import java.lang.reflect.Method; public class ReflectionExample { public static void main(String[] args) throws Exception { // Get the Class object of the String class Class<?> stringClass = String.class; // Get the length () method of the String class Method lengthMethod = stringClass.getMethod("length"); // Create a string object String str = "Hello, Reflection!"; // Call the length () method and output the result int length = (int) lengthMethod.invoke(str); System.out.println("String length: " + length); } } In the above example, we first obtain the class class object of the String class through String.class, and then use the gength () method of the String class using the getMethod () method.Then, we create a string object, then use the infring () method to call the length () method, and output the result to the console.This example demonstrates how to use the reflex mechanism to call the class. To sum up, the reflex technology in the Jboss Reflection framework and the Java class library can obtain and operate information at runtime, and they implement these functions by analyzing bytecode files.The reflection mechanism provides us with a powerful tool that can achieve some advanced functions in many scenarios.By learning and mastering reflective technology, we can better understand and apply Java language.