JAXB继承，unmarshal到marshaled类的子类 [英] JAXB inheritance, unmarshal to subclass of marshaled class

问题描述

我正在使用JAXB来读写XML。我想要的是使用基础JAXB类进行编组，并使用继承的JAXB类进行解组。这是为了允许发送方Java应用程序将XML发送到另一个接收方Java应用程序。发送方和接收方将共享一个通用的JAXB库。我希望接收器将XML解组为特定于接收器的JAXB类，该类扩展了泛型JAXB类。

I'm using JAXB to read and write XML. What I want is to use a base JAXB class for marshalling and an inherited JAXB class for unmarshalling. This is to allow a sender Java application to send XML to another receiver Java application. The sender and receiver will share a common JAXB library. I want the receiver to unmarshall the XML into a receiver specific JAXB class which extends the generic JAXB class.

示例：

这是发件人使用的常见JAXB类。

This is the common JAXB class which is used by the sender.

@XmlRootElement(name="person")
public class Person {
    public String name;
    public int age;
}

这是解组XML时使用的特定于接收器的JAXB类。接收器类具有特定于接收器应用程序的逻辑。

This is the receiver specific JAXB class used when unmarshalling the XML. The receiver class has logic specific to the receiver application.

@XmlRootElement(name="person")
public class ReceiverPerson extends Person {
    public doReceiverSpecificStuff() ...
}

编组按预期工作。问题在于解组，尽管JAXBContext使用了子类 ReceiverPerson 的包名，但它仍然是 Person 的解组。 / p>

Marshalling works as expected. The problem is with unmarshalling, it still unmarshals to Person despite the JAXBContext using the package name of the subclassed ReceiverPerson.

JAXBContext jaxbContext = JAXBContext.newInstance(package name of ReceiverPerson);

我想要的是解组到 ReceiverPerson 。我能够做到这一点的唯一方法是从 Person 中删除​​ @XmlRootElement 。不幸的是，这样做会阻止 Person 被封送。这就好像JAXB从基类开始并向下运行，直到找到具有适当名称的第一个 @XmlRootElement 。我尝试添加 createPerson（）方法，该方法将 ReceiverPerson 返回到 ObjectFactory 但这没有帮助。

What I want is to unmarshall to ReceiverPerson. The only way I've been able to do this is to remove @XmlRootElement from Person. Unfortunately doing this prevents Person from being marshaled. It's as if JAXB starts at the base class and works its way down until it finds the first @XmlRootElement with the appropriate name. I've tried adding a createPerson() method which returns ReceiverPerson to ObjectFactory but that doesn't help.

推荐答案

你正在使用JAXB 2.0吗？ （自JDK6起）

You're using JAXB 2.0 right? (since JDK6)

有一个类：

javax.xml.bind.annotation.adapters.XmlAdapter<ValueType,BoundType>

哪一个可以继承，并覆盖以下方法：

which one can subclass, and override following methods:

public abstract BoundType unmarshal(ValueType v) throws Exception;
public abstract ValueType marshal(BoundType v) throws Exception;

示例：

public class YourNiceAdapter
        extends XmlAdapter<ReceiverPerson,Person>{

    @Override public Person unmarshal(ReceiverPerson v){
        return v;
    }
    @Override public ReceiverPerson marshal(Person v){
        return new ReceiverPerson(v); // you must provide such c-tor
    }
}

用法是完成如下：

@Your_favorite_JAXB_Annotations_Go_Here
class SomeClass{
    @XmlJavaTypeAdapter(YourNiceAdapter.class)
    Person hello; // field to unmarshal
}

我很确定，通过使用这个概念你可以自己控制编组/解组过程（包括选择要构造的正确[sub | super]类型）。

I'm pretty sure, by using this concept you can control the marshalling/unmarshalling process by yourself (including the choice the correct [sub|super]type to construct).

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