我有一个Animal类和一个Animal扩展,称为AnimalExtension。

public class Animal

public class AnimalExtension extends Animal

这两个类之间的唯一区别是AnimalExtension具有另一个称为animalId的实例变量。 Animal没有此实例变量。

我也有自己的数据类型,希望将其封送给XML。此数据类型称为AnimalList。在AnimalList内,有一个Animals列表作为实例变量。

@XmlType(name = "AnimalList")
public class AnimalList{
    private List<Animal> animalList;
    ....

animalList可以包含Animal和AnimalExtension。但是,在XML上,我不希望将该元素命名为AnimalExtension。我希望他们所有人都具有Animal的元素名称。我只希望在JAXB知道Animal实际上是AnimalExtension的实例时显示多余的属性。所以,如果我有一个列表看起来像

List<Animal> animalList = new LinkedList<Animal>();
AnimalExtension animalExtension = new AnimalExtension();
animalExtension.setAnimalId(1);
amimalExtension.setName("Don");

Animal animal = new Animal();
animal.setName("Mike");
animalList.add(animalExtension);
animalList.add(animal);

我希望XML看起来像

<AnimalList>
   <Animal name="Don" id="1" />
   <Animal name="Mike" />
</AnimalList>

这就是我试图做的

    @XmlElements(
    {
            @XmlElement(name = "Animal", type = Animal.class),
            @XmlElement(name = "Animal", type = AnimalExtension.class)
        }
    )
    public List<Animal> getEntries() {
        return animalList;
    }

代码可以编译,但是当我尝试运行服务器时。它给了我这个奇怪的错误,它与正在发生的事情无关(BeanCreationException)。我尝试使XmlElement的名称对于每种类型都不同,并且可以使用,但是这里的挑战是使名称相同。
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'encryptionPayloadContentProvider'

最佳答案

要映射此用例,可以利用以下XmlAdapters:

AnimalAdapter

由于AnimalExtension是Animal的超集,因此我们将使用它来生成/使用XML。然后,我们将利用animalId属性的值来确定是否将Animal或AnimalExtension的实例返回给AnimalList。

import javax.xml.bind.annotation.adapters.XmlAdapter;

public class AnimalAdapter extends XmlAdapter<AnimalExtension, Animal> {

    @Override
    public Animal unmarshal(AnimalExtension animalExtension) throws Exception {
        if(0 != animalExtension.getAnimalId()) {
            return animalExtension;
        }
        Animal animal = new Animal();
        animal.setName(animalExtension.getName());
        return animal;
    }

    @Override
    public AnimalExtension marshal(Animal animal) throws Exception {
        if(animal.getClass() == AnimalExtension.class) {
            return (AnimalExtension) animal;
        }
        AnimalExtension animalExtension = new AnimalExtension();
        animalExtension.setName(animal.getName());
        return animalExtension;
    }

}

IdAdapter

如果其值为0,我们将需要第二个XmlAdapter来抑制animalId:
import javax.xml.bind.annotation.adapters.XmlAdapter;

public class IdAdapter extends XmlAdapter<String, Integer> {

    @Override
    public Integer unmarshal(String string) throws Exception {
        return Integer.valueOf(string);
    }

    @Override
    public String marshal(Integer integer) throws Exception {
        if(integer == 0) {
            return null;
        }
        return String.valueOf(integer);
    }

}

您的模型类将被标注如下:

动物列表
import java.util.ArrayList;
import java.util.List;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;

@XmlRootElement(name="AnimalList")
public class AnimalList {

    private List<Animal> animalList = new ArrayList<Animal>();

    @XmlElement(name="Animal")
    @XmlJavaTypeAdapter(AnimalAdapter.class)
    public List<Animal> getEntries() {
        return animalList;
    }

}

动物
import javax.xml.bind.annotation.XmlAttribute;

public class Animal {

    private String name;

    @XmlAttribute
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

AnimalExtension
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;

public class AnimalExtension extends Animal {

    private int animalId;

    @XmlAttribute(name="id")
    @XmlJavaTypeAdapter(IdAdapter.class)
    public int getAnimalId() {
        return animalId;
    }

    public void setAnimalId(int animalId) {
        this.animalId = animalId;
    }

}

演示代码

以下演示代码可用于演示此解决方案:
import java.io.File;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(AnimalList.class);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        File xml = new File("input.xml");
        AnimalList animalList = (AnimalList) unmarshaller.unmarshal(xml);

        for(Animal animal : animalList.getEntries()) {
            System.out.println(animal.getClass());
        }

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

}

将产生以下输出:
class AnimalExtension
class Animal
<?xml version="1.0" encoding="UTF-8"?>
<AnimalList xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
   <Animal name="Don" id="1"/>
   <Animal name="Mike"/>
</AnimalList>

相关信息

您可能会发现以下信息有用:
  • http://bdoughan.blogspot.com/2010/07/xmladapter-jaxbs-secret-weapon.html
  • http://bdoughan.blogspot.com/2010/07/xmladapter-jaxbs-secret-weapon.html
  • http://bdoughan.blogspot.com/2010/11/jaxb-and-inheritance-using-substitution.html
  • 07-25 21:11