使用注解在子类中覆盖父类私有变量：原理、限制与替代方案

public class Address {
  private Integer postalCode;

  public Integer getPostalCode() {
    return postalCode;
  }

  public void setPostalCode(Integer postalCode) {
    this.postalCode = postalCode;
  }
}

public class ValidateAddress extends Address {
  @NotNull
  @Valid
  private Integer postalCode; // This is a different variable!

  public Integer getPostalCode() {
    return postalCode; // Accesses the postalCode in ValidateAddress
  }

  public void setPostalCode(Integer postalCode) {
    this.postalCode = postalCode; // Modifies the postalCode in ValidateAddress
  }
}

import java.lang.reflect.Field;
import javax.validation.Validation;
import javax.validation.Validator;
import javax.validation.ValidatorFactory;
import javax.validation.constraints.NotNull;

public class ReflectionExample {

    public static void main(String[] args) throws Exception {
        Address address = new Address();
        address.setPostalCode(null); // Setting a null value to trigger validation

        // Get the private field from the parent class
        Field privateField = Address.class.getDeclaredField("postalCode");
        privateField.setAccessible(true); // Allow access to the private field

        // Validate the field using JSR-303 (Bean Validation)
        ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
        Validator validator = factory.getValidator();

        //Create a dummy object to hold the value for validation
        class Dummy {
            @NotNull
            Integer postalCode;

            public Dummy(Integer postalCode) {
                this.postalCode = postalCode;
            }
        }

        Object postalCodeValue = privateField.get(address);
        Dummy dummy = new Dummy((Integer) postalCodeValue);

        var violations = validator.validate(dummy);

        if (!violations.isEmpty()) {
            System.out.println("Validation failed: " + violations);
        } else {
            System.out.println("Validation passed.");
        }
    }
}