Solution: The Data Validator Framework

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.reflect.Field;
// 1. Define the annotation and ensure it survives compilation
@Retention(RetentionPolicy.RUNTIME)
@interface Mandatory {}
class Validator {
    public static void validate(Object obj) {
        Class<?> clazz = obj.getClass();
        
        // 2. Iterate over all declared fields (public, private, protected)
        for (Field field : clazz.getDeclaredFields()) {
            
            // 3. Check if the field is marked as Mandatory
            if (field.isAnnotationPresent(Mandatory.class)) {
                try {
                    // 4. Bypass privacy checks to read the value
                    field.setAccessible(true);
                    Object value = field.get(obj);
                    
                    // 5. Validate the value
                    if (value == null) {
                        throw new RuntimeException("Field " + field.getName() + " is mandatory but null");
                    }
                    
                } catch (IllegalAccessException e) {
                    throw new RuntimeException("Failed to access field " + field.getName(), e);
                }
            }
        }
    }
}
class UserProfile {
    @Mandatory
    private String username;
    
    private String bio; 
    @Mandatory
    private String email;
    public UserProfile(String username, String bio, String email) {
        this.username = username;
        this.bio = bio;
        this.email = email;
    }
}
public class SecurityEventLogger {
    public static void main(String[] args) {
        try {
            System.out.println("Validating user1...");
            UserProfile user1 = new UserProfile("jdoe", "Developer", "jdoe@example.com");
            Validator.validate(user1);
            System.out.println("User1 passed validation.");
            System.out.println("Validating user2...");
            UserProfile user2 = new UserProfile("guest", null, null); 
            Validator.validate(user2);
            System.out.println("User2 passed validation.");
            
        } catch (RuntimeException e) {
            System.out.println("Validation failed: " + e.getMessage());
        }
    }
}