问题＃1

为什么鸟，猫和狗不是数组，为什么使用数组指示符“ []”？

为了获得此JSON表示，您已经将模型与@XmlElementRef注释映射，该注释告诉JAXB使用@XmlRootElement注释的值作为继承指示符。使用MOXy的JSON绑定，这些就成为了关键。因为不允许重复键，所以我们将这些键的值设为JSON数组。

动物园

在模型中@XmlElementRef，您的animals字段/属性上具有注释。

import java.util.Collection;
import javax.xml.bind.annotation.XmlElementRef;

class Zoo {
    @XmlElementRef
    public Collection<? extends Animal> animals;
}

动物

import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.FIELD)
@XmlSeeAlso({Bird.class, Cat.class, Dog.class})
public abstract class Animal {

    private String name;

}

鸟

在每个子类上都有一个@XmlRootElement注释。

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class Bird extends Animal {

    private String wingSpan;
    private String preferredFood;

}

input.json /输出

{
   "bird" : [ {
      "name" : "bird-1",
      "wingSpan" : "6 feets",
      "preferredFood" : "food-1"
   } ],
   "cat" : [ {
      "name" : "cat-1",
      "favoriteToy" : "toy-1"
   } ],
   "dog" : [ {
      "name" : "dog-1",
      "breed" : "bread-1",
      "leashColor" : "black"
   } ]
}

想要查询更多的信息

• http://blog.bdoughan.com/2010/11/jaxb-and-inheritance-using-substitution.html

问题2

第二，是否有摆脱“鸟”，“猫”和“狗”的方法？

您将需要某种继承指示器来表示各种子类。

选项＃1-@XmlDescriminatorNode/@XmlDescriminatorValue

在这里，我使用MOXy的@XmlDescriminatorNode/ @XmlDescriminatorValue注释进行此操作。

动物园

import java.util.Collection;

class Zoo {
    public Collection<? extends Animal> animals;
}

动物

import javax.xml.bind.annotation.*;
import org.eclipse.persistence.oxm.annotations.XmlDiscriminatorNode;

@XmlAccessorType(XmlAccessType.FIELD)
@XmlSeeAlso({Bird.class, Cat.class, Dog.class})
@XmlDiscriminatorNode("@type")
public abstract class Animal {

    private String name;

}

鸟

import org.eclipse.persistence.oxm.annotations.XmlDiscriminatorValue;

@XmlDiscriminatorValue("bird")
public class Bird extends Animal {

    private String wingSpan;
    private String preferredFood;

}

input.json /输出

{
   "animals" : [ {
      "type" : "bird",
      "name" : "bird-1",
      "wingSpan" : "6 feets",
      "preferredFood" : "food-1"
   }, {
      "type" : "cat",
      "name" : "cat-1",
      "favoriteToy" : "toy-1"
   }, {
      "type" : "dog",
      "name" : "dog-1",
      "breed" : "bread-1",
      "leashColor" : "black"
   } ]
}

想要查询更多的信息

• http://blog.bdoughan.com/2010/11/jaxb-and-inheritance-moxy-extension.html

选项＃2-@XmlClassExtractor

ClassExtractor（AnimalExtractor）

您可以编写一些代码，这些代码将根据JSON内容确定适当的子类。

import org.eclipse.persistence.descriptors.ClassExtractor;
import org.eclipse.persistence.sessions.*;

public class AnimalExtractor extends ClassExtractor {

    @Override
    public Class extractClassFromRow(Record record, Session session) {
        if(null != record.get("@wingSpan") || null != record.get("@preferredFood")) {
            return Bird.class;
        } else if(null != record.get("@favoriteToy")) {
            return Cat.class;
        } else {
            return Dog.class;
        }
    }

}

动物

该@XmlClassExtractor注释用于指定ClassExtractor。

import javax.xml.bind.annotation.*;
import org.eclipse.persistence.oxm.annotations.XmlClassExtractor;

@XmlAccessorType(XmlAccessType.FIELD)
@XmlSeeAlso({Bird.class, Cat.class, Dog.class})
@XmlClassExtractor(AnimalExtractor.class)
public abstract class Animal {

    private String name;

}

鸟

由于MOXy处理@XmlElement和@XmlAttribute批注的方式，您想要使可用的任何数据ClassExtractor都需要使用批注@XmlAttribute。

import javax.xml.bind.annotation.XmlAttribute;

public class Bird extends Animal {

    @XmlAttribute
    private String wingSpan;

    @XmlAttribute
    private String preferredFood;

}

input.json /输出

{
   "animals" : [ {
      "wingSpan" : "6 feets",
      "preferredFood" : "food-1",
      "name" : "bird-1"
   }, {
      "favoriteToy" : "toy-1",
      "name" : "cat-1"
   }, {
      "breed" : "bread-1",
      "leashColor" : "black",
      "name" : "dog-1"
   } ]
}

想要查询更多的信息

• http://blog.bdoughan.com/2012/02/jaxb-and-inheritance-eclipselink-moxy.html

演示代码

以下演示代码可与上述两个映射一起使用。

import java.util.*;
import javax.xml.bind.*;
import javax.xml.transform.stream.StreamSource;
import org.eclipse.persistence.jaxb.JAXBContextProperties;

public class Demo {

    public static void main(String[] args) throws Exception {
        Map<String, Object> properties = new HashMap<String, Object>();
        properties.put(JAXBContextProperties.MEDIA_TYPE, "application/json");
        properties.put(JAXBContextProperties.JSON_INCLUDE_ROOT, false);
        JAXBContext jc = JAXBContext.newInstance(new Class[] {Zoo.class}, properties);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        StreamSource json = new StreamSource("src/forum14210676/input.json");
        Zoo zoo = unmarshaller.unmarshal(json, Zoo.class).getValue();

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

}