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;@XmlRootElementpublic 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); }}
