MOXY 中的 JAXB 继承

Question

我有两个班级：

package a;
class A {
 private <type> fieldOfClassA;
 // getters, and setters
}

package b;
class B extends A{
 private <type> fieldOfClassB;
 // getters, and setters
}

我想将 B 类编组到 xml 元素并添加属性 fieldOfClassB 和 A 类的 fieldOfClassA，但它在编组期间会打印以下警告消息：

Ignoring attribute [fieldOfClassA] on class [b.B] as no Property was generated for it.

请注意，这两个类来自两个不同的包，我无法更改此对象模型。

提前谢谢你！

编辑：

我正在使用外部绑定文件。

Answer 1

从您发布的日志消息中，我可以看到您正在使用 MOXy 的外部映射文档（请参阅http://blog.bdoughan.com/2010/12/extending-jaxb-representing-annotations.html）。有几种不同的方法来映射继承的属性。

---

选项 #1 - 将属于父级的继承属性映射

默认情况下，字段/属性需要映射到它所属的类中。由于 MOXy 将外部映射文档限定在包级别，因此您需要为 A 和 B 提供单独的映射文档。

forum10874711/a/binding1.xml

<?xml version="1.0"?>
<xml-bindings
    xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
    package-name="forum10874711.a">
    <java-types>
        <java-type name="A">
            <java-attributes>
                <xml-element java-attribute="fieldOfClassA" name="field-of-class-a"/>
            </java-attributes>
        </java-type>
    </java-types>
</xml-bindings>

forum10874711/b/binding1.xml

<?xml version="1.0"?>
<xml-bindings
    xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
    package-name="forum10874711.b">
    <java-types>
        <java-type name="B">
            <xml-root-element/>
            <java-attributes>
                <xml-element java-attribute="fieldOfClassB" name="field-of-class-b"/>
            </java-attributes>
        </java-type>
    </java-types>
</xml-bindings>

forum10874711/b/jaxb.properties

要将 MOXy 指定为您的 JAXB 实现，您需要在与域模型相同的包中添加一个名为 jaxb.properties 的文件，并使用以下条目。

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory

演示

package forum10874711;

import java.util.*;
import javax.xml.bind.*;
import org.eclipse.persistence.jaxb.JAXBContextFactory;

import forum10874711.b.B;

public class Demo1 {

    public static void main(String[] args) throws Exception {
        Map<String, Object> properties = new HashMap<String, Object>(1);
        List<String> metadata = new ArrayList<String>(2);
        metadata.add("forum10874711/a/binding1.xml");
        metadata.add("forum10874711/b/binding1.xml");
        properties.put(JAXBContextFactory.ECLIPSELINK_OXM_XML_KEY, metadata);
        JAXBContext jc = JAXBContext.newInstance(new Class[] {B.class}, properties);

        B b = new B();
        b.setFieldOfClassA("foo");
        b.setFieldOfClassB(123);

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(b, System.out);
    }

}

输出

<?xml version="1.0" encoding="UTF-8"?>
<b>
   <field-of-class-a>foo</field-of-class-a>
   <field-of-class-b>123</field-of-class-b>
</b>

---

选项 #2 - 映射属于 Child 的继承属性

父类A' can be marked@XmlTransientthis will allow us to map the inherited fields/properties on the child classB`（见http://blog.bdoughan.com/2011/06/ignoring-inheritance-with-xmltransient.html）。

forum10874711/a/binding2.xml

<?xml version="1.0"?>
<xml-bindings
    xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
    package-name="forum10874711.a">
    <java-types>
        <java-type name="A" xml-transient="true"/>
    </java-types>
</xml-bindings>

forum10874711/b/binding2.xml

<?xml version="1.0" encoding="UTF-8"?>
<xml-bindings
    xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
    package-name="forum10874711.b">
    <java-types>
        <java-type name="B">
            <xml-root-element/>
            <java-attributes>
                <xml-element java-attribute="fieldOfClassA" name="field-of-class-a"/>
                <xml-element java-attribute="fieldOfClassB" name="field-of-class-b"/>
            </java-attributes>
        </java-type>
    </java-types>
</xml-bindings>

演示

package forum10874711;

import java.util.*;
import javax.xml.bind.*;
import org.eclipse.persistence.jaxb.JAXBContextFactory;

import forum10874711.b.B;

public class Demo2 {

    public static void main(String[] args) throws Exception {
        Map<String, Object> properties = new HashMap<String, Object>(1);
        List<String> metadata = new ArrayList<String>(2);
        metadata.add("forum10874711/a/binding2.xml");
        metadata.add("forum10874711/b/binding2.xml");
        properties.put(JAXBContextFactory.ECLIPSELINK_OXM_XML_KEY, metadata);
        JAXBContext jc = JAXBContext.newInstance(new Class[] {B.class}, properties);

        B b = new B();
        b.setFieldOfClassA("foo");
        b.setFieldOfClassB(123);

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(b, System.out);
    }

}

输出

<?xml version="1.0" encoding="UTF-8"?>
<b>
   <field-of-class-a>foo</field-of-class-a>
   <field-of-class-b>123</field-of-class-b>
</b>