Spring Rest & Jackson: Empty values are transformed in Null values in XML transformation

Question

For an app working with:

• Spring Framework 4.3.3
• Jackson 2.8.2, modules used:
  • jackson-annotations
  • jackson-core
  • jackson-databind
  • jackson-dataformat-xml (it disables JAXB 2 annotations)

I use jackson for JSON and XML.

About Spring for Rest working according with:

@PutMapping(value="/{id}", 
            consumes={MediaType.APPLICATION_XML_VALUE,  
                      MediaType.APPLICATION_JSON_UTF8_VALUE})

and

@PostMapping(value="/{id}", 
             consumes={MediaType.APPLICATION_XML_VALUE,         
                       MediaType.APPLICATION_JSON_UTF8_VALUE})

And for both scenarios exists the following parameter:

@Validated @RequestBody Persona persona,

The Persona class is declared how:

@JacksonXmlRootElement(localName="persona")
public class Persona implements Serializable {

    @JacksonXmlProperty(localName="id")
    @JsonProperty("id")
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }

    @JacksonXmlProperty(localName="nombre")
    @JsonProperty("nombre")
    public String getNombre() {
        return nombre;
    }
    public void setNombre(String nombre) {
        this.nombre = nombre;
    }
    ...

Note validation annotations (@NotNull, @Size etc) have not been included above

Now about Testing for validation data purposes:

for an Entity with:

null values such as:

person.setNombre(null)
person.setApellido(null)

empty values (of course, it only applies for String type) such as:

person.setNombre("")
person.setApellido("")

When I use the invalid objects to be transformed in JSON and then is send to the rest method in JSON, I can confirm that when the data is transformed to Java again (Remember @Validated @RequestBody Persona persona), through logging I can confirm:

Null scenario:

Invalid data is: Persona [id=null, nombre=null, apellido=null, ...] 

Empty scenario:

Invalid data is: Persona [id=, nombre=, apellido=, ...] 

for JSON I have

public static String objectToJson(Object object) throws JsonProcessingException {
        ObjectWriter ow = new ObjectMapper().writer().withDefaultPrettyPrinter();
        String json = ow.writeValueAsString(object);
        return json;
    }

Until here all is ok.

The problem is with XML

Working with:

public static String objectToXml(Object object) throws JsonProcessingException {
        XmlMapper xmlMapper = new XmlMapper();
        return xmlMapper.writeValueAsString(object);
    }

I did realize the following when the data invalid objects are transformed to XML to be sent to the rest controller when it arrives and is transformed again Java, the following happens:

Null scenario:

Invalid data is: Persona [id=null, nombre=null, apellido=null, ...] 

Empty scenario:

Invalid data is: Persona [id=null, nombre=null, apellido=null, ...]

The problem is for the Empty scenario: the data arrives or is transformed how null. It should be

Invalid data is: Persona [id=, nombre=, apellido=, ...] 

I need the data how an 'empty' value, not how a null value

Therefore how is possible fix this? I am assuming I need an extra configuration in some place.

BTW, Jackson for XML in Spring is:

@Bean
public MappingJackson2XmlHttpMessageConverter mappingJackson2XmlHttpMessageConverter(){
    MappingJackson2XmlHttpMessageConverter converter = new MappingJackson2XmlHttpMessageConverter();
        converter.setObjectMapper(jackson2ObjectMapperBuilder().createXmlMapper(true).build());
    converter.setPrettyPrint(true);
    converter.setDefaultCharset(StandardCharsets.UTF_8);
        converter.setSupportedMediaTypes(Arrays.asList(MediaType.APPLICATION_XML));
    return converter;
}

@Bean
public Jackson2ObjectMapperBuilder jackson2ObjectMapperBuilder(){
    Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();
    builder.simpleDateFormat("yyyy-MM-dd");
    return builder;
}

What I need:

Hello, What I need is the following:

If I send an Entity with null values for any field, it must arrives to the rest controller and the @RequestBody Persona must contains the same the null values for the same fields, same thought if the Entity contains empty values and it is sent. It works how is expected in JSON

It only happens for XML when the Entity has null values for any field. When the Entity has empty values for any field. The @RequestBody Persona contains null values, it does not keep the empty values, they have been transformed how null instead. I need keep the same empty values.

Therefore if the Entity has been sent with either null or empty values or both, I need that JSON and XML when the @RequestBody Persona works, it contains the same null or empty values for the same fields how they have been defined originally.

Note seems it is a bug, closely related with:

• XML Empty tag to Empty string in the object during xml deserialization