EclipseLink MOXy JSON序列化
我有一个示例课程：
class Zoo { public Collection animals; } 当使用MOXy序列化时，我得到：
{ "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" } ] }
为什么它使用数组指示符“[]”，而鸟，猫和狗不是数组？ 第二，有没有办法摆脱“鸟”，“猫”和“狗”？
换句话说，我试图去：
{ { "name": "bird-1", "wingSpan": "6 feets", "preferredFood": "food-1" } , { "name": "cat-1", "favoriteToy": "toy-1" } , { "name": "dog-1", "breed": "bread-1", "leashColor": "black" } }
谢谢，Behzad
问题＃1
为什么它使用数组指示符“[]”，而鸟，猫和狗不是数组？
要获得此JSON表示，您已使用@XmlElementRef注释映射模型，该注释告诉JAXB使用@XmlRootElement注释的值作为inheritance指示符。 使用MOXy的JSON绑定，这些成为关键。 我们创建这些键JSON数组的值，因为不允许键重复。
动物园
在您的模型中，您在animals字段/属性上有@XmlElementRef注释。
import java.util.Collection; import javax.xml.bind.annotation.XmlElementRef; class Zoo { @XmlElementRef public Collection 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" } ] }
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问题2
第二，有没有办法摆脱“鸟”，“猫”和“狗”？
您将需要某种inheritance指示符来表示各种子类。
选项＃1 – @XmlDescriminatorNode / @XmlDescriminatorValue
在这里，我使用MOXy的@XmlDescriminatorNode / @XmlDescriminatorValue注释来完成此操作。
动物园
import java.util.Collection; class Zoo { public Collection 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" } ] }
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选项＃2 – @XmlClassExtractor
ClassExtractor（AnimalExtractor）
您可以编写一些代码，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
@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如何处理@XmlElement和@XmlAttribute注释，因此需要使用@XmlAttribute注释要为ClassExtractor提供的任何数据。
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" } ] }
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演示代码
以下演示代码可与上述两种映射一起使用。
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 properties = new HashMap(); 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); } }