How I can retrieve null value, when unmarshalling, if inside XML attribute value is empty ? Now I make inside my getters checking for null :
public String getLabel() {
if (label.isEmpty()) {
return null;
}
else {
return label;
}
}
But may be exist some other, more elegant way?
Thanks.
I think your XML looks more or less like this:
<myElement></myElement>
This, unfortunately, means, that you are passing an empty string.
If you want to pass null you have two options:
<myElement/> tag at all).xsi:nil.If using xsi:nil, first you have to declare your xml element (in XSD file) as nilable, like this:
<xsd:element name="myElement" nillable="true"/>
Then, to pass the null value inside XML do this:
<myElement xsi:nil="true"/>
or this:
<myElement xsi:nil="true"></myElement>
This way, JAXB knows, that you are passing null instead of an empty String.
The answer given by npe is a good one, and specifying how you want null represented would be my recommendation as well. To have xsi:nil marshalled you will want to annotate your property as (see Binding to JSON & XML - Handling Null):
@XmlElement(nillable=true)
public String getLabel() {
return label;
}
If you don't want to change your XML representation then you could use an XmlAdapter:
EmptyStringAdapter
package forum10869748;
import javax.xml.bind.annotation.adapters.XmlAdapter;
public class EmptyStringAdapter extends XmlAdapter<String, String> {
@Override
public String unmarshal(String v) throws Exception {
if("".equals(v)) {
return null;
}
return v;
}
@Override
public String marshal(String v) throws Exception {
return v;
}
}
Foo
You reference an XmlAdapter through the use of the @XmlJavaTypeAdapter annotation. If you would like this XmlAdapter applied to all Strings then you could register it at the package level (see JAXB and Package Level XmlAdapters).
package forum10869748;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
@XmlRootElement
public class Foo {
private String label;
@XmlJavaTypeAdapter(EmptyStringAdapter.class)
public String getLabel() {
return label;
}
public void setLabel(String label) {
this.label = label;
}
}
Demo
package forum10869748;
import java.io.File;
import javax.xml.bind.*;
public class Demo {
public static void main(String[] args) throws Exception {
JAXBContext jc = JAXBContext.newInstance(Foo.class);
Unmarshaller unmarshaller = jc.createUnmarshaller();
File xml = new File("src/forum10869748/input.xml");
Foo foo = (Foo) unmarshaller.unmarshal(xml);
System.out.println(foo.getLabel());
}
}
input.xml
<?xml version="1.0" encoding="UTF-8"?>
<foo>
<label></label>
</foo>
Output
null
JAXB. But in my opinion, what you propose here, is dangerous. Treating empty strings as nulls without any notification that nulls are possible in contract (WSDL, XSD) is a kind of monkey-patching, and it's almost certain, that someone, someday will be getting really, really frustrated debugging this. If you want to treat empty strings and nulls the same, I'd suggest using isBlank(String) from commons-lang
@XmlElement(nillable=true) and explicitly representing null in the XML is the best way to go (I even upvoted your answer). I added this answer for those people how cannot change the XML representation. I don't consider it dangerous, as long as the user is consistent with what empty elements mean.