Hibernate Validator and Jackson: Using the @JsonPr

问题:

Say I have a simple POJO like below annotated with Jackson 2.1 and Hibernate Validator 4.3.1 annotations:

final public class Person {
  @JsonProperty("nm")
  @NotNull
  final public String name;

  public Person(String name) {
      this.name = name;
  }
}

And I send JSON like such to a web service:

{"name": null}

Hibernate when it reports the ConstraintViolation uses the class member identifier "name" instead of the JsonProperty annotation value. Does anyone know if it is possible to make the Hibernate Validator look at the annotation of the class and use that value instead?

回答1:

No, that's not possible. Hibernate Validator 5 (Bean Validation 1.1) has the notion of ParameterNameProviders which return the names to reported in case method parameter constraints are violated but there is nothing comparable for property constraints.

回答2:

Unfortunately there is no easy way to do it. But here are some insights that can help you:

Parsing constraint violations

From the ConstraintViolationException, you can get a set of ConstraintViolation, that exposes the constraint violation context:

• ConstraintViolation#getLeafBean(): If it is a bean constraint, this method returns the bean instance in which the constraint is applied to.
• ConstraintViolation#getPropertyPath(): Returns the path to the invalid property.

From the property path, you can get the leaf node:

Path propertyPath = constraintViolation.getPropertyPath();
Optional<Path.Node> leafNodeOptional = 
        StreamSupport.stream(propertyPath.spliterator(), false).reduce((a, b) -> b);

Then check if the type of the node is PROPERTY and get its name:

String nodeName = null;

if (leafNodeOptional.isPresent()) {
    Path.Node leafNode = leafNodeOptional.get();
    if (ElementKind.PROPERTY == leafNode.getKind()) {
        nodeName = leafNode.getName();
    }
}

Introspecting a class with Jackson

To get the available JSON properties from the leaf bean class, you can introspect it with Jackson (see this answer and this answer for further details):

Class<?> beanClass = constraintViolation.getLeafBean().getClass();
JavaType javaType = mapper.getTypeFactory().constructType(beanClass);

BeanDescription introspection = mapper.getSerializationConfig().introspect(javaType);
List<BeanPropertyDefinition> properties = introspection.findProperties();

Then filter the properties by comparing the leaf node name with the Field name from the BeanPropertyDefinition:

Optional<String> jsonProperty = properties.stream()
        .filter(property -> nodeName.equals(property.getField().getName()))
        .map(BeanPropertyDefinition::getName)
        .findFirst();

Using JAX-RS?

With JAX-RS (if you are using it), you can define an ExceptionMapper to handle ConstraintViolationExceptions:

@Provider
public class ConstraintViolationExceptionMapper 
                 implements ExceptionMapper<ConstraintViolationException> {

    @Override
    public Response toResponse(ConstraintViolationException exception) {
        ...
    }
}

To use the ObjectMapper in your ExceptionMapper, you could provide a ContextResolver<T> for it:

@Provider
public class ObjectMapperContextResolver implements ContextResolver<ObjectMapper> {

    private final ObjectMapper mapper;

    public ObjectMapperContextResolver() {
        mapper = createObjectMapper();
    }

    @Override
    public ObjectMapper getContext(Class<?> type) {
        return mapper;
    }

    private ObjectMapper createObjectMapper() {
        ObjectMapper mapper = new ObjectMapper();
        mapper.configure(SerializationFeature.INDENT_OUTPUT, true);
        mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
        return mapper;
    }
}

Inject the Providers interface in your ExceptionMapper:

@Context
private Providers providers;

Lookup for your ContextResolver<T> and then get the ObjectMapper instance:

ContextResolver<ObjectMapper> resolver = 
        providers.getContextResolver(ObjectMapper.class, MediaType.WILDCARD_TYPE);
ObjectMapper mapper = resolver.getContext(ObjectMapper.class);

If you are interested in getting @XxxParam names, refer to this answer.