使用JAXB解组时将空元素转换为null

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement(name = "person")
public class Person {

    private String firstName;
    private String middleName;

    @XmlElement(nillable = true)
    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    @XmlElement(nillable = true)
    public String getMiddleName() {
        return middleName;
    }

    public void setMiddleName(String middleName) {
        this.middleName = middleName;
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<person xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
   <firstName>John</firstName>
   <middleName xsi:nil="true"/>
</person>

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;
import java.io.StringReader;

public class JAXBExample {

    public static void main(String[] args) {
        String xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" +
               <person xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\">\n" +
                "   <firstName>John</firstName>\n" +
                "   <middleName xsi:nil=\"true\"/>\n" +
                "</person>";

        try {
            JAXBContext jaxbContext = JAXBContext.newInstance(Person.class);
            Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();
            StringReader reader = new StringReader(xml);
            Person person = (Person) jaxbUnmarshaller.unmarshal(reader);

            System.out.println("First name: " + person.getFirstName());
            System.out.println("Middle name: " + person.getMiddleName()); // Should be null
        } catch (JAXBException e) {
            e.printStackTrace();
        }
    }
}

First name: John
Middle name: null