[英]How do Inheritance and JAXB work together?
public abstract class Parent<T> {
protected List<T> list;
@XmlTransient //Question why do we have to give this here?
public abstract List<T> getList();
public abstract void setList(List<T> list);
}
@XmlRootElement(name = "child1")
class Child1 extends Parent<ExtendedElement1>{
@Override
public void setList(List<ExtendedElement1> list){
this.list = list;
}
@Override
@XmlElementWrapper(name = "child1-list")
@XmlElement(name = "child-list-element")
public List<ExtendedElement1> getList(){
return this.list;
}
}
@XmlRootElement(name = "child2")
class Child2 extends Parent<ExtendedElement2>{
@Override
public void setList(List<ExtendedElement2> list){
this.list = list;
}
@Override
@XmlElementWrapper(name = "child1-list")
@XmlElement(name = "child-list-element")
public List<ExtendedElement2> getList(){
return this.list;
}
}
class Element{
@XmlElement(name = "integer", type = int.class)
private int i = 2;
}
class ExtendedElement1 extends Element{
@XmlElement(name = "extended-element1-str", type = String.class)
private String str = "hello";
}
class ExtendedElement2 extends Element{
@XmlElement(name = "extended-element2-str", type = String.class)
private String str1 = "hello_there";
}
正如我在示例中所示,当我从Parent
类getList()
方法中删除 @XmlTransient
时,以下xml被编组:
<child1>
<!-- List is serialized 2 times -->
<list xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="extendedElement1">
<integer>2</integer>
<extended-element1-str>hello</extended-element1-str>
</list>
<list xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="extendedElement1">
<integer>2</integer>
<extended-element1-str>hello</extended-element1-str>
</list>
<list xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="extendedElement1">
<integer>2</integer>
<extended-element1-str>hello</extended-element1-str>
</list>
<child1-list>
<child-list-element>
<integer>2</integer>
<extended-element1-str>hello</extended-element1-str>
</child-list-element>
<child-list-element>
<integer>2</integer>
<extended-element1-str>hello</extended-element1-str>
</child-list-element>
<child-list-element>
<integer>2</integer>
<extended-element1-str>hello</extended-element1-str>
</child-list-element>
</child1-list>
</child1>
但是当我添加 @XmlTransient
注释时,就像在示例中一样,xml被序列化,只需要一个列表。
<child1>
<child1-list>
<child-list-element>
<integer>2</integer>
<extended-element1-str>hello</extended-element1-str>
</child-list-element>
<child-list-element>
<integer>2</integer>
<extended-element1-str>hello</extended-element1-str>
</child-list-element>
<child-list-element>
<integer>2</integer>
<extended-element1-str>hello</extended-element1-str>
</child-list-element>
</child1-list>
</child1>
所以请有人解释一下为什么需要在Parent Class getter方法中提供@XmlTransient
? 对于这些情况,继承和JAXB如何相互关联?
为什么会发生这种情况
JAXB(JSR-222)实现会将其知道的每个域对象映射到复杂类型。 这意味着它认为Parent
类存在以下XML类型(当list
不是@XmlTransient
)。
<xs:complexType name="parent" abstract="true">
<xs:sequence>
<xs:element name="list" type="xs:anyType" nillable="true" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
现在Child2
也有一个复杂的类型。 JAXB可以完成两件事:
child2
类型扩展parent
。 这意味着它从parent
类型中获取所有元素以及它自己的元素。 <xs:complexType name="child2">
<xs:complexContent>
<xs:extension base="parent">
<xs:sequence>
<xs:element name="child1-list" minOccurs="0">
<xs:complexType>
<xs:sequence>
<xs:element name="child-list-element" type="extendedElement2" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:extension>
</xs:complexContent>
如何修复它
您可以将@XmlTransient
放在Parent
类的list
属性中,但我建议使用@XmlTransient
注释Parent
类。
import java.util.List;
import javax.xml.bind.annotation.XmlTransient;
@XmlTransient
public abstract class Parent<T> {
protected List<T> list;
public abstract List<T> getList();
public abstract void setList(List<T> list);
}
这将把它作为映射类删除,对应于Child2
的复杂类型将变为:
<xs:complexType name="child2">
<xs:sequence>
<xs:element name="child1-list" minOccurs="0">
<xs:complexType>
<xs:sequence>
<xs:element name="child-list-element" type="extendedElement2" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
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