如何告诉JAXB，该元素是“根之子”？

Question

I have some test data in XML format, that I want to map to POJO.

<Root>
   <Child1>
      <Data>
      </Data>
   </Child1>
   <Child2>
      <Data>
      </Data>
   </Child2>
</Root>

Child1 is the first Object and Child2 the second.

JAXBContext context = JAXBContext.newInstance(classesToLoad);
Unmarshaller um = context.createUnmarshaller();
Object obj = (Object) um.unmarshal(data);

Object in this case is just a placeholder

@Getter
@Setter
@XmlRootElement(name = "TestData")
public class Child1 {

    @XmlElement(name = "ID")
    private String ID;
}

.

This is the code I'm working with right now, but I get this exception:

javax.xml.bind.UnmarshalException: unexpected Element (URI:"", lokal:"TestData"). expectected elements are: Child1

Answer 1

Move the annotation

@XmlRootElement(name = "TestData")

To your Root class and change it to

@XmlRootElement(name = "Root")

And I believe you'll need

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "Child1")

in the Child1 class.

And give it a go again.

What the exception tells you is it's expecting an element of name TestData with namespace "" (you can ignore namespace for now since it's blank, but take minute or two to have a look at this since it's something that can trip you up when working with XML for the first time), and it's because you define the root element as TestData.

Additionally, the data example you've provided does not seem to correspond to your designed class.

<Child1>
    <Data>
    </Data>
</Child1>

public class Child1 {

    @XmlElement(name = "ID")
    private String ID;
}

I don't know if you've replaced the enclosed data for brevity for the sake of a neater question, but your Java object would more closely resemble this XML.

<Child1>
   <ID>[String ID value]</ID>
</Child1>