How to parse JSON's array of numbers - json

Question

I'm facing the following situation parsing a JSON.
The JSON I want to unmarshal contains an array of numbers (doubles) like this:
"position":[52.50325,13.39062]
So there is no name/value pairs.
The Problem is that I can't get the value of this array. In the Java object modeling the JSON I defined the position attribute as list of Doubles: List<Double> but after the unmarshel, the position attribute is always null.
For testing purpose I changed the content of the JSON like that:
position: [„52.50325“ ,“ 13.39062“ ]
and then there is no issue, I get the list with two elements. (Btw, this happens regardless if the position is defined as list of Strings or list of Doubles (List<String> or List<Double>))
So a workaround could be to alter the JSON response and mark this numbers as string before unmarshaling it, but I would like to avoid that, and I’m wondering if there is solution to get the value of a number array?
Here is a snapshot from the code:
ResultsListDO.java:
#XmlElement(required = true)
protected List<Double> position;
public List<Double> getPosition()
{
if (position == null) {
position = new ArrayList<Double>();
}
return this.position;
}
JSON unmarshal:
context = new JSONJAXBContext(JSONConfiguration.mapped().build(), ResultsListDO.class);
JSONUnmarshaller um = context.createJSONUnmarshaller();
ResultsListDO resultsList = um.unmarshalFromJSON(source.getReader(), ResultsListDO.class);

Answer 1

Note: I'm the EclipseLink JAXB (MOXy) lead and a member of the JAXB (JSR-222) expert group.
Unless you have annotated your class with #XmlAccessorType(XmlAccessType.FIELD) the problem is probably that your annotation is on the field rather than the get method (see: http://blog.bdoughan.com/2011/06/using-jaxbs-xmlaccessortype-to.html).
import java.util.*;
import javax.xml.bind.annotation.XmlElement;
public class Foo {
protected List<Double> position;
#XmlElement(required = true)
public List<Double> getPosition()
{
if (position == null) {
position = new ArrayList<Double>();
}
return this.position;
}
}
Demo Code
Below I'll demonstrate that everything works using MOXy as the JSON-binding provider.
jaxb.properties
To specify MOXy as your JAXB provider you need to include a file called jaxb.properties in the same package as your domain model with the following entry (see: http://blog.bdoughan.com/2011/05/specifying-eclipselink-moxy-as-your.html).
javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory
Demo
import java.util.*;
import javax.xml.bind.*;
import javax.xml.transform.stream.StreamSource;
import org.eclipse.persistence.jaxb.JAXBContextProperties;
public class Demo {
public static void main(String[] args) throws Exception {
Map<String, Object> properties = new HashMap<String,Object>();
properties.put(JAXBContextProperties.MEDIA_TYPE, "application/json");
properties.put(JAXBContextProperties.JSON_INCLUDE_ROOT, false);
JAXBContext jc = JAXBContext.newInstance(new Class[] {Foo.class}, properties);
Unmarshaller unmarshaller = jc.createUnmarshaller();
StreamSource json = new StreamSource("src/forum18355753/input.json");
Foo foo = unmarshaller.unmarshal(json, Foo.class).getValue();
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(foo, System.out);
}
}
input.json/Output
{
"position" : [ 52.50325, 13.39062 ]
}