EclipseLink MOXy JSON序列化

Question

EclipseLink MOXy JSON序列化

11

我有一个示例类：

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

使用 MOXy 进行序列化时，我得到了：

{
    "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"
        }
    ]
}

为什么使用数组指标 "[]"，而鸟、猫和狗不是数组？另外，有没有办法摆脱 "bird"、"cat" 和 "dog"？

换句话说，我想得到：

{
        {
            "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

- Behzad Pirvali

1个回答

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- bdoughan · Accepted Answer

问题 #1

为什么使用数组标识符 "[]"，而鸟、猫和狗不是数组？

为了获得这个JSON表示，您已经使用@XmlElementRef注释将您的模型映射起来，该注释告诉JAXB将@XmlRootElement注释的值用作继承指示符。使用MOXy的JSON绑定，它们变成了键。我们使这些键的值成为JSON数组，因为不允许重复键。

动物园

在您的模型中，您将@XmlElementRef注释放在了animals字段/属性上。

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，你都有一个 @XmlRootElement 注解。

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class Bird extends Animal {

    private String wingSpan;
    private String preferredFood;

}

输入.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"
   } ]
}

有关jaxb和使用替换的继承

问题#2

第二，有没有办法摆脱“鸟”，“猫”和“狗”？

你需要某种继承指示器来表示各个子类。

选项1 - @XmlDescriminatorNode/@XmlDescriminatorValue

在这里，我使用 MOXy 的 @XmlDescriminatorNode/@XmlDescriminatorValue 注释来完成此操作。

Zoo

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;

}

输入.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"
   } ]
}

更多信息

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来根据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;

}

Bird

由于 MOXy 如何处理 @XmlElement 和 @XmlAttribute 注释，您希望在 ClassExtractor 中提供任何数据都需要用 @XmlAttribute 进行注释。

import javax.xml.bind.annotation.XmlAttribute;

public class Bird extends Animal {

    @XmlAttribute
    private String wingSpan;

    @XmlAttribute
    private String preferredFood;

}

输入.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"
   } ]
}

了解更多

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<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);
    }

}