使用 JAXB 从 JSON 中解组嵌套对象 [英] Unmarshalling nested objects from JSON with JAXB

问题描述

我正在尝试使用 Eclipselink 将输入 JSON 解组为 JAXB 对象.但是，当我尝试这样做时，我发现嵌套对象最终被设置为空.我可以尝试自己解组嵌套对象，它会一直工作到必须解组另一个嵌套对象，然后将其设置为 null.

I'm trying to unmarshall input JSON into JAXB objects with Eclipselink. However, when I try to do this, I find that nested objects end up being set as null. I can try and unmarshall the nested object by itself, and it will work up until the point that it has to unmarshall a further nested object, which is also then set to null.

以这个类为例:

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "event", propOrder = {
"objectBs"
})
public class ObjectA
implements Serializable
{

    private final static long serialVersionUID = 56347348765454329L;
    @XmlElement(required = true)
    protected ObjectA.ObjectBs objectBs;

    public ObjectA.ObjectBs getObjectBs() {
        return objectBs;
    }

    public void setObjectBs(ObjectA.ObjectBs value) {
        this.objectBs = value;
    }

    public boolean isSetObjectBs() {
        return (this.objectBs!= null);
    }

    @XmlAccessorType(XmlAccessType.FIELD)
    @XmlType(name = "", propOrder = {
        "objectB"
    })
    public static class ObjectBs
        implements Serializable
    {

        private final static long serialVersionUID = 56347348765454329L;
        @XmlElement(required = true)
        protected List<ObjectB> objectB;

        public List<ObjectB> getObjectB() {
            if (objectB == null) {
                objectB = new ArrayList<ObjectB>();
            }
            return this.objectB;
        }

        public boolean isSetObjectB() {
            return ((this.objectB!= null)&&(!this.objectB.isEmpty()));
        }

        public void unsetObjectB() {
            this.objectB = null;
        }

    }
}

ObjectA 有一个名为 ObjectBs 的对象，其中包含 ObjectB 的列表.当我尝试解组此类时，ObjectA 拥有的任何其他字段都将被正确填充，并且 ObjectBs 对象将被创建，但 ObjectB 的列表将为空.但是，如果我自己解组一个 ObjectB，它将创建它的字段填充，直到它自己的嵌套对象.

Where ObjectA has an object called ObjectBs which contains a list of ObjectB. When I try unmarshalling this class, any other field that ObjectA has would be correctly filled, and the ObjectBs object would be created, but the list of ObjectB would be empty. But, if I unmarshall just one ObjectB by itself, it will be created with it's fields filled, up until it's own nested objects.

这是我用来解组 JSON 的代码:

This is the code I'm using to unmarshall the JSON:

JAXBContext jc = JAXBContextFactory.createContext(
    "com.package1"
    + ":com.package2"
    + ":com.package3"
    , null);
Unmarshaller um = jc.createUnmarshaller();
um.setProperty("eclipselink.media-type", "application/json"); 
um.setProperty(MarshallerProperties.JSON_INCLUDE_ROOT, false);
ObjectA objA = unmarshaller.unmarshal(new StreamSource(
    new StringReader(json)), ObjectA.class).getValue();

还有一些 JSON 示例:

And some example JSON:

        {
                "objectBs": [
                    {
                        "a": "blahblah",
                        "b": 123456,
                        "c": "abc blah 123 blah",
                        "nestedObject": {
                            "evenMoreNestedObjects": {
                                "d": "blah",
                                "e": "blahblahblah",
                                "anotherNestedObject": {
                                    "x": 25,
                                    "y": 50
                                }
                        }}}]
        }

推荐答案

你没有提供你试图解组的 JSON，但我做了一些逆向工程，下面是一个使用你的模型的例子发布在您的问题中:

You didn't provide the JSON you are trying to unmarshal, but I've done a little reverse engineering and below is an example that works using the model you posted in your question:

import javax.xml.bind.*;
import javax.xml.transform.stream.StreamSource;
import org.eclipse.persistence.jaxb.MarshallerProperties;
import org.eclipse.persistence.jaxb.UnmarshallerProperties;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(ObjectA.class);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        unmarshaller.setProperty(UnmarshallerProperties.MEDIA_TYPE, "application/json");
        unmarshaller.setProperty(UnmarshallerProperties.JSON_INCLUDE_ROOT, false);
        StreamSource json = new StreamSource("src/forum17866155/input.json");
        ObjectA objectA = unmarshaller.unmarshal(json, ObjectA.class).getValue();

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(MarshallerProperties.MEDIA_TYPE, "application/json");
        marshaller.setProperty(MarshallerProperties.JSON_INCLUDE_ROOT, false);
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(objectA, System.out);
    }

}

input.json/Output

{
   "objectBs" : {
      "objectB" : [ {
      }, {
      } ]
   }
}

这篇关于使用 JAXB 从 JSON 中解组嵌套对象的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！