如何使JAXB unmarshaller忽略前缀？

问题描述

我有以下XML：

<ns2:Person name="John" age="20" />

我想将它解组为从XSD生成的JAXB对象Person。

And I want to unmarshal it to JAXB object Person which was generated from the XSD.

这是我正在运行的代码：

this is the code I'm running:

JAXBContext context = JAXBContext.newInstance(PersoEntity.class);
Unmarshaller um = context.createUnmarshaller();
StringReader sr = new StringReader(xml);
Person p = (Person)um.unmarshal(sr);

令人惊讶的是我得到以下例外：

Surprisingly I get the following exception:

javax.xml.bind.UnmarshalException
 - with linked exception:
[org.xml.sax.SAXParseException: The prefix "ns2" for element "ns2:Person" is not bound.]

我该如何解决？谢谢

推荐答案

获得碎片

您当前获取XML片段的方式导致命名空间声明丢失。在您的片段 ns2 不再是前缀，您只需要一个带冒号的元素名称（ ns2：Person ）。这将导致名称空间感知解析器出现问题。下面的文章可能是您获取XML片段的更好方法：

The way that you are currently getting the XML fragment is causing the namespace declarations to be lost. In your fragment ns2 is no longer a prefix, you just have a element name with a colon in it (ns2:Person). This is going to cause problems with namespace aware parsers. The article below may be a better approach for you to get the XML fragment:

• http://blog.bdoughan.com/2012/08/handle-middle-of-xml-document-with-jaxb.html

处理您的使用案例

使用你拥有的XML片段，你可以创建一个 XMLFilter ，它从XML元素中删除前缀，然后利用JAXB的 UnmarshallerHandler 进行解组。

Using the XML fragment that you have, you could create an XMLFilter that removes the prefix from the XML element, and then leverage JAXB's UnmarshallerHandler to do the unmarshalling.

演示

Demo

package forum11968399;

import java.io.StringReader;
import javax.xml.bind.*;
import javax.xml.parsers.*;
import org.xml.sax.*;
import org.xml.sax.helpers.XMLFilterImpl;

public class Demo {

    private static final String xml = "<ns2:Person name='John' age='20' />";

    public static void main(String[] args) throws Exception {
        SAXParserFactory spf = SAXParserFactory.newInstance();
        SAXParser sp = spf.newSAXParser();
        XMLReader xmlReader = sp.getXMLReader();
        XMLFilter xmlFilter = new MyXMLFilter(xmlReader);

        JAXBContext context = JAXBContext.newInstance(PersonEntity.class);
        Unmarshaller um = context.createUnmarshaller();
        UnmarshallerHandler unmarshallerHandler = um.getUnmarshallerHandler();
        xmlFilter.setContentHandler(unmarshallerHandler);

        StringReader sr = new StringReader(xml);
        xmlFilter.parse(new InputSource(sr));
        PersonEntity p = (PersonEntity) unmarshallerHandler.getResult();
    }

    private static class MyXMLFilter extends XMLFilterImpl {

        public MyXMLFilter(XMLReader xmlReader) {
            super(xmlReader);
        }

        @Override
        public void startElement(String uri, String localName, String qName,
                Attributes attributes) throws SAXException {
            int colonIndex = qName.indexOf(':');
            if(colonIndex >= 0) {
                qName = qName.substring(colonIndex + 1);
            }
uri = XML_NAMESPACE; //to prevent unknown XML element exception, we have to specify the namespace here
            super.startElement(uri, localName, qName, attributes);
        }

        @Override
        public void endElement(String uri, String localName, String qName)
                throws SAXException {
            int colonIndex = qName.indexOf(':');
            if(colonIndex >= 0) {
                qName = qName.substring(colonIndex + 1);
            }
            super.endElement(uri, localName, qName);
        }

    }

}

PersonEntity

PersonEntity

package forum11968399;

import javax.xml.bind.annotation.*;

@XmlRootElement(name="Person")
@XmlAccessorType(XmlAccessType.FIELD)
public class PersonEntity {

    @XmlAttribute
    private String name;

    @XmlAttribute
    private int age;

}

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