JAXB unmarshaller.unmarshal 何时返回 JAXBElement<MySchemaObject>还是一个 MySchemaObject? [英] when does JAXB unmarshaller.unmarshal returns a JAXBElement<MySchemaObject> or a MySchemaObject?

问题描述

我有两个代码，在两个不同的 java 项目中，做几乎相同的事情，(根据 xsd 文件解组 web 服务的输入).

I have two codes, in two different java projects, doing almost the same thing, (unmarshalling the input of a webservice according to an xsd-file).

但在一种情况下我应该这样写:(输入是一个占位符名称)(元素是 OMElement 输入)

But in one case I should write this: (Input is a placeholder name) ( element is OMElement input )

ClassLoader clInput = input.ObjectFactory.class.getClassLoader();
JAXBContext jc = JAXBContext.newInstance("input", clInput);
Unmarshaller unmarshaller = jc.createUnmarshaller();
Input input = (Input)unmarshaller.unmarshal( element.getXMLStreamReader() );

在另一个库中，我必须使用 JAXBElement.getValue()，因为它是一个返回的 JAXBElement，而一个简单的 (Input) 转换只会崩溃:

and in the other lib I must use JAXBElement.getValue(), because it is a JAXBElement that is returned, and a simple (Input) cast simply crashes:

Input input = (Input)unmarshaller.unmarshal( element.getXMLStreamReader() ).getValue();

你知道是什么导致了这种差异吗?

Do you know what leads to such a difference ?

推荐答案

如果根元素唯一对应于一个 Java 类，那么将返回该类的一个实例，否则将返回一个 JAXBElement被退回.

If the root element uniquely corresponds to a Java class then an instance of that class will be returned, and if not a JAXBElement will be returned.

如果您想确保始终获得域对象的实例，您可以利用 JAXBInstrospector.下面是一个例子.

If you want to ensure that you always get an instance of the domain object you can leverage the JAXBInstrospector. Below is an example.

演示

package forum10243679;

import java.io.StringReader;
import javax.xml.bind.*;
import javax.xml.transform.stream.StreamSource;

public class Demo {

    private static final String XML = "<root/>";

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Root.class);
        Unmarshaller unmarshaller = jc.createUnmarshaller();
        JAXBIntrospector jaxbIntrospector = jc.createJAXBIntrospector();

        Object object = unmarshaller.unmarshal(new StringReader(XML));
        System.out.println(object.getClass());
        System.out.println(jaxbIntrospector.getValue(object).getClass());

        Object jaxbElement = unmarshaller.unmarshal(new StreamSource(new StringReader(XML)), Root.class);
        System.out.println(jaxbElement.getClass());
        System.out.println(jaxbIntrospector.getValue(jaxbElement).getClass());
    }

}

输出

class forum10243679.Root
class forum10243679.Root
class javax.xml.bind.JAXBElement
class forum10243679.Root

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