在JaxB编组中初始化对象和嵌套对象

Question

我有这个对象：

ClassRoom.java

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class ClassRoom {

	@XmlElementWrapper(required = true)
	private List<Person> students;
	
	@XmlElement
	private Person teacher;
	
	@XmlElement(nillable = true)
	private String name;
	
	public List<Person> getStudents() {
		return students;
	}
	
	public void setStudents(List<Person> students) {
		this.students = students;
	}
	
	public Person getTeacher() {
		return teacher;
	}
	
	public void setTeacher(Person teacher) {
		this.teacher = teacher;
	}
	
	public String getName() {
		return name;
	}
	
	public void setName(String name) {
		this.name = name;
	}
}

使用此子对象类：

Person.java

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Person {

	@XmlElement(nillable = true)
	private String name;
	
	private String lastname;
	private BigDecimal moneySaved;
	private List<String> certifications;
	private String ubication;
	
	public String getName() {
		return name;
	}
	
	public void setName(String name) {
		this.name = name;
	}
	
	public String getLastname() {
		return lastname;
	}
	
	public void setLastname(String lastname) {
		this.lastname = lastname;
	}
	
	public BigDecimal getMoneySaved() {
		return moneySaved;
	}
	
	public void setMoneySaved(BigDecimal moneySaved) {
		this.moneySaved = moneySaved;
	}
	
	public List<String> getCertifications() {
		return certifications;
	}
	
	public void setCertifications(List<String> certifications) {
		this.certifications = certifications;
	}
	
	public String getUbication() {
		return ubication;
	}
	
	public void setUbication(String ubication) {
		this.ubication = ubication;
	}
}

我必须编组此结构，但是在某些情况下，ClassRoom实例的每个属性都可能为null。在这种情况下，XML输出必须如下：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<classRoom xmlns="emp">
    <name></name>
    <teacher>
      <name></name>
      <lastname></lastname>
      <moneySaved></moneySaved>
      <certifications></certifications>
      <ubication></ubication>
    </teacher>
    <students></students>
</classRoom>

但是当我在这些对象的字段中使用nillable = true属性时，为了在null时显示空标签，XML看起来像这样：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<classRoom xmlns="emp">
    <name xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
    <students xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
    <teacher xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
</classRoom>

我有以下问题（将对象编组为XML时）：

• 是否可以从空表示形式标记中删除xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"部分？

• 当根对象为null时，是否有任何选项或实现来编组空对象（及其嵌套对象）？