java - JAXB: how to make JAXB NOT to unmarshal empty string to 0

Question

I have a DTO class with a field such as:

@XmlAttribute
@NotNull
private Integer number = null;

I'm trying to unmarshal xml such as

...  number=""  ...

I need the nuber field to stay null, so that a validation exception would be thrown. Instead JAXB unmarshals it as 0. How can I make it to behave correctly ?

Answer 1

Arguable, it is behaving correctly. number="" does not mean null, it's an empty String, and JAXB is having to try and handle that correctly, and it decides that the closest thing to empty string for an Integer data type is zero. If you wanted a null, then the number attribute should be omitted altogether.

If you want to customise this behaviour, you need to write a subclass of javax.xml.bind.annotation.adapters.XmlAdapter which can handle the conversion between raw String and the boundtype (i.e. between String and Integer) in the way you want. You then wire up that adaptor by annotating the field with @XmlJavaTypeAdapter.