From Spring BindingResult to field JSONPath/JSON Pointer, with Jackson

Question

I have a Spring Boot application using javax.validation annotations and I'm trying to return friendly JSON error messages pointing to the offending field, yet converting from the available "Java-object" path to either JSONPath or JSON Pointer is something I'm not finding a way to do.

SSCO sample:

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.PropertyNamingStrategy;

import javax.validation.Valid;
import javax.validation.Validation;
import javax.validation.Validator;
import javax.validation.ValidatorFactory;
import javax.validation.constraints.Min;
import java.util.List;

public class Test {

    public static void main(String[] args) throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        mapper.setPropertyNamingStrategy(PropertyNamingStrategy.SNAKE_CASE);

        Data data = new Data();
        System.out.println("Serialized: " + mapper.writerWithDefaultPrettyPrinter().writeValueAsString(data));

        ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
        Validator validator = factory.getValidator();
        validator.validate(data).forEach(violation -> {
            System.out.println("Path: " + violation.getPropertyPath());
        });
    }

    public static class Data {
        @JsonProperty("foobar")
        @Valid
        public List<Foo> foo = List.of(new Foo());
    }
    public static class Foo {
        @Min(100)
        public int barBaz = 42;
    }

}

Output:

Serialized: {
  "foobar" : [ {
    "bar_baz" : 42
  } ]
}
Path: foo[0].barBaz

As you can see, I need to convert foo[0].barBaz into either $.foobar[0].bar_baz or /foobar/0/bar_baz. The parsed object (the data variable above) is also provided by the BindingResult object that holds the validation information.

I thought about doing some String manipulation, but that's messy, hacky, and can break easily with @JsonProperty which I would need to handle separately, maybe other corner cases that I didn't think about. Plus, we use SNAKE_CASE as a standard, changing to simplify the task is not a solution.

I suppose Jackson's ObjectMapper could be used somehow to make this conversion, or some other piece of Jackson API, but I couldn't find anything about that. Any other library that can do this is also fine (ideally it should understand Jackson annotations like @JsonProperty).

Answer 1

You can do it easily with Hibernate Validator 6.1.5.

You need to provide your own implementation of PropertyNodeNameProvider.

By implementing it, we can define how the name of a property will be resolved during validation. In our case, we want to read the value from the Jackson configuration.

Creating a validator:

 ValidatorFactory validatorFactory = Validation.byProvider( HibernateValidator.class )
        .configure()
        .propertyNodeNameProvider(new JacksonPropertyNodeNameProvider())
        .buildValidatorFactory();

JacksonPropertyNodeNameProvider:

public class JacksonPropertyNodeNameProvider implements PropertyNodeNameProvider {

  private final ObjectMapper objectMapper = new ObjectMapper();

  @Override
  public String getName(Property property) {
    if ( property instanceof JavaBeanProperty ) {
        return getJavaBeanPropertyName( (JavaBeanProperty) property );
    }

    return getDefaultName( property );
  }

  private String getJavaBeanPropertyName(JavaBeanProperty property) {
    JavaType type = objectMapper.constructType( property.getDeclaringClass() );
    BeanDescription desc = objectMapper.getSerializationConfig().introspect( type );

    return desc.findProperties()
            .stream()
            .filter( prop -> prop.getInternalName().equals( property.getName() ) )
            .map( BeanPropertyDefinition::getName )
            .findFirst()
            .orElse( property.getName() );
  }

  private String getDefaultName(Property property) {
    return property.getName();
  }
}

More details You can find in documentation: