有没有可能在Spring Boot中实现一个POJO，它有一个表示复合主键的字段，而不使用JPA或嵌套类？

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface CompositeKey {
}

public class User {
    @CompositeKey
    private String userId;
    private String username;
    private String email;
    
    // 省略构造方法、getter和setter
}

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;

import java.lang.reflect.Field;

@Component
public class CompositeKeyResolver implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        Class<?> clazz = bean.getClass();
        Field[] fields = clazz.getDeclaredFields();
        
        for (Field field : fields) {
            if (field.isAnnotationPresent(CompositeKey.class)) {
                // 将该字段设置为复合主键
                // 例如，可以使用反射设置字段的某个属性
            }
        }
        
        return bean;
    }
    
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
}

@SpringBootApplication
@EnableAspectJAutoProxy
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}