How does the Java reflection mechanism work with the reflector itself?

Java reflection mechanism allows exploring the reflector itself, and annotations on the Method object can be obtained through reflection, including annotation type and value.

Java reflection mechanism is used in the reflector itself

Java reflection mechanism allows the program to inspect and modify the structure of the class at runtime, But it is rarely used to explore the reflection mechanism itself. This article will use a practical case to show how to use the reflection mechanism to study the operation of the reflector.

Case: Get the Annotation on the

Method

object. We can use reflection to get the Method Annotations attached to the object. Here is the sample code:

import java.lang.annotation.Annotation;
import java.lang.reflect.Method;

public class Main {
    public static void main(String[] args) {
        try {
            // 获取 Method 对象
            Method method = Main.class.getMethod("annotatedMethod");
            
            // 使用反射获取注解
            Annotation[] annotations = method.getAnnotations();
            
            // 遍历并打印注解
            for (Annotation annotation : annotations) {
                System.out.println(annotation);
            }
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }
    }
    
    @MyAnnotation("Hello, World!")
    public void annotatedMethod() { }
}

Result:

@MyAnnotation(value=Hello, World!)

Parsing:

• We first use Main.class.getMethod("annotatedMethod") Gets the Method object of the annotatedMethod method of the Main class.
• Then we use method.getAnnotations() to get all the annotations on the method and store them in the annotations array.
• Finally, we loop through the annotations array and print the type and value of each annotation.

This example shows how to use the reflection mechanism to obtain the annotations on the Method object. The same principle can be used to explore any other aspect of the reflection mechanism, for example:

• Get the parent class and interface of the class
• Get the type and value of the field
• Modify the attributes of the class (such as access rights)

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