Java反射解析注解

package com.jeeplus.config;

import javax.validation.constraints.Size;
import java.lang.annotation.Annotation;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Arrays;

/**
 * @author Mr.css
 * @version 2022-10-08 9:51
 */
public class Test {

    @Size(groups = {Test.class})
    private String name;

    public static void main(String[] args) throws NoSuchFieldException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        Class<?> clazz = Test.class;

        // 遍历 name 字段上的注解
        Field field = clazz.getDeclaredField("name");
        Annotation[] annotations = field.getAnnotations();
        // 因为只有 1 个注解，所以读到的必定是 @Size
        for (Annotation annotation: annotations){
            Class<?> cla = annotation.annotationType();
            // 注解的字段，看起来是 field，实际上是 method，需要通过 invoke() 获取属性值
            Method method = cla.getDeclaredMethod("groups");
            Class<?>[] groups = (Class<?>[]) method.invoke(annotation);
            System.out.println(Arrays.toString(groups));
        }
    }
}