JAXB-Eclipselink：映射抽象“getter”到XML [英] JAXB-Eclipselink: Mapping abstract "getter" to XML
问题描述
我正在使用JAXB的EclipseLink实现（2.3）将POJO映射到XML并遇到以下用例的问题：
I am using the EclipseLink implementation (2.3) of JAXB to map POJOs to XML and encountering a problem with following usecase:
public abstract class A {
public abstract Set<X> getX();
// There is no setter
}
public class B extends A {
// Set via constructor
private Set<X> x;
@Override
public Set<X> getX();
}
我在外部绑定中完全定义了映射本身 - 文件，我将A类设置为瞬态，如下所示：
I am defining the mapping itself completely in an external bindings-file, i set class A to be transient like so:
<java-type name="foo.A" xml-transient="true"/>
和B类：
<java-type name="bar.B" xml-accessor-type="PROPERTY">
<xml-root-element name="B" />
<java-attributes>
<xml-element java-attribute="x" xml-path="..."/>
</java-attributes>
</java-type>
现在，在编组时我得到了异常：在课堂上找到了名为[x]的重复属性[ bar.B]
在我看来是来自A中的抽象声明，由B继承。
Now, upon marshalling i am getting the exception: "Duplicate Property named [x] found on class [bar.B]" which in my opinion is coming from the abstract declaration in A, being inherited by B.
将B的访问者类型设置为FIELD，摆脱这个错误，遗憾的是这不是一个选项，因为我在B中有一个额外的属性来编组，它不会返回一个字段而是一个计算值，所以我坚持使用PROPERTY（以下作品：设置访问器类型for B to FIELD并使用@XmlPath注释映射额外属性 - 但我不希望在我的代码中注释。）
Setting the accessor-type for B to FIELD, gets rid of this error, unfortunately this is not an option because i do have an extra property in B to marshal which does not return a field but a calculated value, so i am stuck with PROPERTY (following works: setting accessor-type for B to FIELD and mapping the extra property with an @XmlPath annotation - but i dont want annotations in my code).
坚持使用类B的访问器类型PROPERTY ，我的下一次尝试是：
Being stuck with accessor-type PROPERTY for class B, my next attempt was:
<java-type name="foo.A" xml-accessor-type="NONE"/>
防止抽象属性被B继承，这让我得到：
to prevent the abstract property from being inherited by B, which gets me:
Ignoring attribute [x] on class [bar.B] as no Property was generated for it.
使用此映射也是如此：
<java-type name="foo.A" xml-accessor-type="PROPERTY">
<java-attributes>
<xml-transient java-attribute="x"/>
</java-attributes>
</java-type>
在这两种情况下，属性'x'都会被忽略。
In both cases property 'x' is ignored.
我现在花了相当多的时间在这上面 - 我无法想象它不可能让它起作用吗？
I have really spent quite some time on this now - i cant imagine that its not possible to get this to work??
我现在的解决方法：
让foo.A成为临时的，为bar.B指定访问者类型的FIELD（它使我的属性'x'没有问题）并在B中映射额外的属性在代码中使用注释。
但如前所述：我想在没有注释的情况下完全解决这个问题 - 任何人都有任何想法？布莱斯？ ：）
Leaving foo.A to be transient, specifying accessor-type FIELD for bar.B (which gets me property 'x' without problems) and mapping the extra property in B using an annotation in code. But as mentioned before: I would like to solve this completely without annotations - anybody any idea? Blaise? :)
问候，
- qu
推荐答案
注意：我是 EclipseLink JAXB（MOXy） 领导和 JAXB 2（JSR-222） 专家组。
Note: I'm the EclipseLink JAXB (MOXy) lead and a member of the JAXB 2 (JSR-222) expert group.
您似乎遇到了错误。您可以通过以下链接跟踪我们在此问题上的进展。我在下面提供了有关此问题的其他详细信息：
You appear to have hit a bug. You can track our progress on this issue at the following link. I have provided additional details on this issue below:
- https://bugs.eclipse.org/367886
使用注释
如果您要使用JAXB / MOXy注释映射此用例，可以设置 @XmlAccessorType（XmlAccessType.NONE）在 A 类上执行以下操作：
If you were going to map this use case with JAXB/MOXy annotations you could set @XmlAccessorType(XmlAccessType.NONE) on the A class and do something like:
A
A
package forum8727402;
import javax.xml.bind.annotation.*;
@XmlAccessorType(XmlAccessType.NONE)
public abstract class A {
public abstract String getX();
}
B
B
package forum8727402;
import javax.xml.bind.annotation.*;
import org.eclipse.persistence.oxm.annotations.XmlPath;
@XmlRootElement
public class B extends A {
@XmlPath("a/b/c/text()")
private String x;
public B() {
x = "Hello World";
}
@Override
public String getX() {
return x;
}
@XmlElement
public String getCalculatedValue() {
return "Calculated Value";
}
}
演示
Demo
package forum8727402;
import javax.xml.bind.*;
public class Demo {
public static void main(String[] args) throws Exception {
JAXBContext jc = JAXBContext.newInstance(B.class);
B b = new B();
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(b, System.out);
}
}
输出
Output
<?xml version="1.0" encoding="UTF-8"?>
<b>
<a>
<b>
<c>Hello World</c>
</b>
</a>
<calculatedValue>Calculated Value</calculatedValue>
</b>
使用MOXy的外部映射文件
oxm.xml
oxm.xml
以下是代表等效内容的 MOXy外部映射文件之前显示的注释：
Below is a MOXy external mapping file that represents the equivalent of the previously shown annotations:
<?xml version="1.0" encoding="UTF-8"?>
<xml-bindings
xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
package-name="forum8727402">
<java-types>
<java-type name="A" xml-accessor-type="NONE"/>
<java-type name="B">
<xml-root-element/>
<java-attributes>
<xml-element java-attribute="x" xml-path="a/b/c/text()"/>
<xml-element java-attribute="calculatedValue"/>
</java-attributes>
</java-type>
</java-types>
</xml-bindings>
演示
Demo
下面的代码演示了如何引用映射文件：
The code below demonstrates how to reference the mapping file:
package forum8727402;
import java.util.*;
import javax.xml.bind.*;
import org.eclipse.persistence.jaxb.JAXBContextFactory;
public class Demo {
public static void main(String[] args) throws Exception {
Map<String, Object> properties = new HashMap<String, Object>(1);
properties.put(JAXBContextFactory.ECLIPSELINK_OXM_XML_KEY, "forum8727402/oxm.xml");
JAXBContext jc = JAXBContext.newInstance(new Class[] {A.class, B.class}, properties);
B b = new B();
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(b, System.out);
}
}
输出
Output
[EL Warning]: 2012-01-04 14:45:46.366--Ignoring attribute [x] on class [forum8727402.xml.B] as no Property was generated for it.
<?xml version="1.0" encoding="UTF-8"?>
<b>
<calculatedValue>Calculated Value</calculatedValue>
</b>
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