For my springboot application / framework, I would like to create a custom Constraint Validator to validate Configuration Properties upon application startup. Based upon a different boolean property, I would like to conditionally log and suppress the constraint instead of failing application startup.

As an example, consider a custom annotation DeprecatedField which based upon the property my.props.fail-on-deprecation would either:

• fail application startup (if an annotated property is non-null and my.props.fail-on-deprecation==true)
• or create a warning log and continue with startup (if an annotated property is non-null and my.props.fail-on-deprecation==false)

Example Classes

// DeprecatedField.java
@Target({METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER, TYPE_USE})
@Retention(RUNTIME)
@Documented
@Constraint(validatedBy = DeprecatedFieldValidator.class)
public @interface DeprecatedField {
  String message() default "the property is deprecated and should be removed";
  Class<?>[] groups() default {};
  Class<? extends Payload>[] payload() default {};
}

// DeprecatedFieldValidator.java
@Slf4j
@RequiredArgsConstructor
public class DeprecatedFieldValidator implements ConstraintValidator<DeprecatedField, Object> {
  
  @Override
  public void initialize(DeprecatedField annotation) {}

  @Override
  public boolean isValid(Object value, ConstraintValidatorContext context) {
    // warn / error if the annotated property is used
    return value == null;
  }
}

// CustomConfig.java

@Slf4j
@Data
@Component
@Validated
@ConfigurationProperties(prefix = "my.custom.props", ignoreUnknownFields = false)
public class CustomConfig { 
    @NotBlank
    private String foo;
    
    @DeprecatedField
    private String bar;

Desired Outcome

• If the application.yml properties contained:

  my:
    props:
      fail-on-deprecation: true
    custom:
      props:
        foo: "value1"
        bar: "value2"
  

  Then I would want the constraint to fail application startup ie:

  ***************************
  APPLICATION FAILED TO START
  ***************************
  
  Description:
  
  Binding to target org.springframework.boot.context.properties.bind.BindException: Failed to bind properties under 'my.custom.props' to com.CustomConfig failed:
  
      Property: my.custom.props.bar
      Value: "value2"
      Reason: the property is deprecated and should be removed
  

• If the application.yml properties contained:

  my:
    props:
      fail-on-deprecation: false
    custom:
      props:
        foo: "value1"
        bar: "value2"
  

  Then I would want to suppress the constraint and start the application, but add a warning log with similar information

  WARN - Deprecated Properties Violation
  
      Property: my.custom.props.bar
      Value: "value2"
      Reason: the property is deprecated and should be removed
  

I have tried 2 options

• Option (1) Autowire the boolean property into the constraint validator and conditionally generate the violation

  Something similar to

  // DeprecatedFieldValidator.java
  @Slf4j
  @RequiredArgsConstructor
  public class DeprecatedFieldValidator implements ConstraintValidator<DeprecatedField, Object> {
  
    @Value("${my.props.fail-on-deprecation:false}"
    private boolean failOnDeprecation;
  
    @Override
    public void initialize(DeprecatedField annotation) {}
  
    @Override
    public boolean isValid(Object value, ConstraintValidatorContext context) {
      // warn if not failing and the annotated property is used
      if (!failOnDeprecation) {
        // TODO: not sure how to get the full property path of "my.custom.props.bar" for this log
        log.warn("WARN - Deprecated Properties Violation");
      }
  
      // fail only if fail flag enabled and deprecated property are used
      return !failOnDeprecation || value == null;
    }
  }
  

• Option (2) Create a custom configurationPropertiesValidator bean that is a child of LocalValidatorFactoryBean and overrides the processConstraintViolations method to filter the violations of our custom DeprecatedField annotation

  // DeprecationValidatorFactoryBean.java
  @Slf4j
  @Component("configurationPropertiesValidator")
  @RequiredArgsConstructor
  public class DeprecationValidatorFactoryBean extends LocalValidatorFactoryBean {
  
    @Value("${my.props.fail-on-deprecation:false}"
    private boolean fail;
  
  
    @Override
    protected void processConstraintViolations(Set<ConstraintViolation<Object>> violations, Errors errors) {
      // if fail==true - then return all violations
      // if fail==false - then filter (remove) and log DeprecationField Violations
      Set<ConstraintViolation<Object>> deprecationFilteredViolations = (fail) ?
        violations :
        this.filterDeprecationViolations(violations, errors);
      super.processConstraintViolations(deprecationFilteredViolations, errors);
    }
  
    // ...
  }
  

Option (1) functionally works, but I’m not sure how to access the property path (ie: my.custom.props.bar) for the warning log

Option (2) seems to work, but seems more complex than in may need to be as this approach requires indirect usage of the "configurationPropertiesValidator" bean and the custom annotations to function. If another dependency happens to use the "configurationPropertiesValidator", then there will be conflict.

Question:

• How can the desired behavior be achieved?
  • Is there a way to achieve the desired logging outcome (with the full property name) using option (1)?
  • Is there another recommended pattern via spring / spring boot for achieving this desired behavior?