我有一个示例类:

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

当用 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"
        }
    ]
}

为什么用数组指标“[]”，而bird、cat、dog不是数组？ 二、有没有办法去掉“bird”、“cat”、“dog”？

换句话说，我正在尝试:

{
        {
            "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， 贝扎德

最佳答案

问题 #1

Why is it using array indicators "[]", while bird, cat, and dog are not arrays?

要获得此 JSON 表示，您已使用 @XmlElementRef 注释映射您的模型，该注释告诉 JAXB 使用 @XmlRootElement 注释的值作为继承指示符。通过 MOXy 的 JSON 绑定(bind)，这些成为键。我们将这些键的值设为 JSON 数组，因为键不允许重复。

动物园

在您的模型中，您的 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<? 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"
   } ]
}

了解更多信息

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

问题#2

Second, is there a way to get rid of "bird", "cat", and "dog"?

您将需要某种继承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 注释来执行此操作。

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"
   } ]
}

了解更多信息

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

选项 #2 - @XmlClassExtractor

类提取器(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 处理 @XmlElement 和 @XmlAttribute 注释的方式，您希望提供给 ClassExtractor 的任何数据将需要使用 @XmlAttribute 进行注释。

import javax.xml.bind.annotation.XmlAttribute;

public class Bird extends Animal {

    @XmlAttribute
    private String wingSpan;

    @XmlAttribute
    private String preferredFood;

}

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"
   } ]
}

了解更多信息

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

演示代码

以下演示代码可用于上述两种映射。

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);
    }

}

关于java - EclipseLink MOXy JSON 序列化，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/14210676/