还是以在第一节介绍JAXB的schema为例：
<?xml version="1.0" encoding="UTF-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema" xmlns:tns="http://www.liulutu.com/students/"
targetNamespace="http://www.liulutu.com/students/">
<element name="students">
<complexType>
<sequence>
<element name="student" type="tns:StudentType" maxOccurs="unbounded" />
</sequence>
</complexType>
</element>
<simpleType name="SexType">
<restriction base="string">
<enumeration value="Male"></enumeration>
<enumeration value="Female"></enumeration>
</restriction>
</simpleType>
<complexType name="StudentType">
<attribute name="sex" type="tns:SexType"></attribute>
<attribute name="name" type="string"></attribute>
</complexType>
</schema>
生成的类文件如下：
从Schema定义里可以看出，Students里包含有多个StudentType对象：
@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "", propOrder = {
"student"
})
@XmlRootElement(name = "students")
public class Students {
@XmlElement(required = true)
protected List<StudentType> student;
/**
* Gets the value of the student property.
*
* <p>
* This accessor method returns a reference to the live list,
* not a snapshot. Therefore any modification you make to the
* returned list will be present inside the JAXB object.
* This is why there is not a <CODE>set</CODE> method for the student property.
*
* <p>
* For example, to add a new item, do as follows:
* <pre>
* getStudent().add(newItem);
* </pre>
*
*
* <p>
* Objects of the following type(s) are allowed in the list
* {@link StudentType }
*
*
*/
public List<StudentType> getStudent() {
if (student == null) {
student = new ArrayList<StudentType>();
}
return this.student;
}
}
现在的问题是，从StudentType对象里，怎么能访问到它的父对象也就是上面的students对象呢？StudentType类如下：
@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "StudentType")
public class StudentType {
@XmlAttribute(name = "sex")
protected SexType sex;
@XmlAttribute(name = "name")
protected String name;
@XmlAttribute(name = "birthday")
@XmlJavaTypeAdapter(Adapter1 .class)
@XmlSchemaType(name = "date")
protected Calendar birthday;
/**
* Gets the value of the sex property.
*
* @return
* possible object is
* {@link SexType }
*
*/
public SexType getSex() {
return sex;
}
/**
* Sets the value of the sex property.
*
* @param value
* allowed object is
* {@link SexType }
*
*/
public void setSex(SexType value) {
this.sex = value;
}
/**
* Gets the value of the name property.
*
* @return
* possible object is
* {@link String }
*
*/
public String getName() {
return name;
}
/**
* Sets the value of the name property.
*
* @param value
* allowed object is
* {@link String }
*
*/
public void setName(String value) {
this.name = value;
}
/**
* Gets the value of the birthday property.
*
* @return
* possible object is
* {@link String }
*
*/
public Calendar getBirthday() {
return birthday;
}
/**
* Sets the value of the birthday property.
*
* @param value
* allowed object is
* {@link String }
*
*/
public void setBirthday(Calendar value) {
this.birthday = value;
}
}
从类定义可以看出，其中没有任何描述Students对象的信息。
解决方法：
首先，假设要解析的文件内容如下：
<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <ns2:students xmlns:ns2="http://www.liulutu.com/students/"> <student sex="Female" name="Bob" birthday="2003-11-27+08:00" /> <student sex="Male" name="Lisa" birthday="2003-10-26+08:00" /> </ns2:students>
（如果手头没有文件，也可以用以上模型快速的生成一个，例如：）
StudentType studentType = new StudentType();
studentType.setBirthday(Calendar.getInstance());
studentType.setName("Bob");
studentType.setSex(SexType.FEMALE);
Students students = new Students();
students.getStudent().add(studentType);
JAXBContext context = JAXBContext.newInstance(Students.class);
Marshaller marshaller = context.createMarshaller();
marshaller.marshal(students, new File("a.xml"));
方法一：使用afterUnmarshal(Unmarshaller u, Object parent)方法
首先修改一下StudentType类，增加一个用来存取父对象的变量：
private Students parent;
public Students getParent() {
return parent;
}
因为模型是由JAXB直接读取和生成的，因此我们不能通过简单的setParent()来设置parent对象。
可以在生成的模型类中添加一个public void afterUnmarshal(Unmarshaller u, Object parent) 方法，这个方法在每次构建完模型后都会调用（甚至我们什么接口实现，类继承都不需要声明就会自动调用），其中的parent参数就是我们期望的父模型对象，因此可以直接把这个parent对象设置成我们期望的parent对象：
public void afterUnmarshal(Unmarshaller u, Object parent) {
if (parent instanceof Students) {
this.parent = (Students)parent;
}
}
可以检验一下：
JAXBContext context = JAXBContext.newInstance(Students.class);
Unmarshaller unmarshaller = context.createUnmarshaller();
Students students = (Students) unmarshaller.unmarshal(new File("a.xml"));
List<StudentType> student = students.getStudent();
for(StudentType st: student){
System.out.println(st.getName());
System.out.println(st.getParent());
}
方法二：使用Binder
方法一简单易用，但是缺点就是需要修改模型，这里介绍的方法就不需要修改模型，只是在读取的时候需要有点不一样：
首先我们用普通的Dom方式读取文件内容：
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(true);
Document document = factory.newDocumentBuilder().parse(new File("a.xml"));
然后创建JAXBContext对象和Binder对象：
JAXBContext context = JAXBContext.newInstance(Students.class); Binder<Node> binder = context.createBinder();
最后用Binder对象去解析模型的和链接父子关系：
Students students = (Students) binder.updateJAXB(document.getDocumentElement());
List<StudentType> student = students.getStudent();
for(StudentType st: student){
System.out.println(st.getName());
Node xmlNode = binder.getXMLNode(st);
Object parent = binder.getJAXBNode(xmlNode.getParentNode());
System.out.println(parent);
}
方法三 使用Unmarshall.Listener监听
除了以上两种方法，还可以使用监听的方式，在marshall的过程中构建父子关系，有点类似于方法一
JAXBContext context = JAXBContext.newInstance(Students.class);
Unmarshaller unmarshaller = context.createUnmarshaller();
final Map<StudentType, Students> map = new HashMap<StudentType, Students>();
unmarshaller.setListener(new Listener() {
public void afterUnmarshal(Object target, Object parent) {
super.afterUnmarshal(target, parent);
if(target instanceof StudentType && parent instanceof Students){
map.put((StudentType)target, (Students) parent);
}
}
});
Students students = (Students) unmarshaller.unmarshal(new File("a.xml"));
List<StudentType> student = students.getStudent();
for(StudentType st: student){
System.out.println(st.getName());
System.out.println(map.get(st));
}