Java JAXB：如何在解组 XML 文档期间忽略命名空间？

JAXB: How to ignore namespace during unmarshalling XML document?

提问by Eugene Yokota

My schema specifies a namespace, but the documents don't. What's the simplest way to ignore namespace during JAXB unmarshalling (XML -> object)?

我的架构指定了一个命名空间，但文档没有。在 JAXB 解组（XML -> 对象）期间忽略命名空间的最简单方法是什么？

In other words, I have

换句话说，我有

<foo><bar></bar></foo>

instead of,

代替，

<foo xmlns="http://tempuri.org/"><bar></bar></foo>

采纳答案by VonC

I believe you must add the namespaceto your xml document, with, for example, the use of a SAX filter.

我相信您必须将命名空间添加到您的 xml 文档中，例如，使用SAX 过滤器。

That means:

这意味着：

• Define a ContentHandler interface with a new class which will intercept SAX events before JAXB can get them.
• Define a XMLReader which will set the content handler

• 使用新类定义 ContentHandler 接口，该类将在 JAXB 获取 SAX 事件之前拦截它们。
• 定义一个 XMLReader，它将设置内容处理程序

then link the two together:

然后将两者链接在一起：

public static Object unmarshallWithFilter(Unmarshaller unmarshaller,
java.io.File source) throws FileNotFoundException, JAXBException 
{
    FileReader fr = null;
    try {
        fr = new FileReader(source);
        XMLReader reader = new NamespaceFilterXMLReader();
        InputSource is = new InputSource(fr);
        SAXSource ss = new SAXSource(reader, is);
        return unmarshaller.unmarshal(ss);
    } catch (SAXException e) {
        //not technically a jaxb exception, but close enough
        throw new JAXBException(e);
    } catch (ParserConfigurationException e) {
        //not technically a jaxb exception, but close enough
        throw new JAXBException(e);
    } finally {
        FileUtil.close(fr); //replace with this some safe close method you have
    }
}

回答by mafro

Another way to add a default namespace to an XML Document before feeding it to JAXB is to use JDom:

在将默认名称空间提供给 JAXB 之前将默认名称空间添加到 XML 文档的另一种方法是使用JDom：

1. Parse XML to a Document
2. Iterate through and set namespace on all Elements
3. Unmarshall using a JDOMSource

1. 将 XML 解析为文档
2. 迭代并在所有元素上设置命名空间
3. 使用 JDOMSource 解组

Like this:

像这样：

public class XMLObjectFactory {
    private static Namespace DEFAULT_NS = Namespace.getNamespace("http://tempuri.org/");

    public static Object createObject(InputStream in) {
        try {
            SAXBuilder sb = new SAXBuilder(false);
            Document doc = sb.build(in);
            setNamespace(doc.getRootElement(), DEFAULT_NS, true);
            Source src = new JDOMSource(doc);
            JAXBContext context = JAXBContext.newInstance("org.tempuri");
            Unmarshaller unmarshaller = context.createUnmarshaller();
            JAXBElement root = unmarshaller.unmarshal(src);
            return root.getValue();
        } catch (Exception e) {
            throw new RuntimeException("Failed to create Object", e);
        }
    }

    private static void setNamespace(Element elem, Namespace ns, boolean recurse) {
        elem.setNamespace(ns);
        if (recurse) {
            for (Object o : elem.getChildren()) {
                setNamespace((Element) o, ns, recurse);
            }
        }
    }

回答by Kristofer

Here is an extension/edit of VonCs solution just in case someone doesn′t want to go through the hassle of implementing their own filter to do this. It also shows how to output a JAXB element without the namespace present. This is all accomplished using a SAX Filter.

这是 VonCs 解决方案的扩展/编辑，以防万一有人不想经历实现自己的过滤器来执行此操作的麻烦。它还展示了如何在不存在命名空间的情况下输出 JAXB 元素。这一切都是使用 SAX 过滤器完成的。

Filter implementation:

过滤器实现：

import org.xml.sax.Attributes;
import org.xml.sax.SAXException;

import org.xml.sax.helpers.XMLFilterImpl;

public class NamespaceFilter extends XMLFilterImpl {

    private String usedNamespaceUri;
    private boolean addNamespace;

    //State variable
    private boolean addedNamespace = false;

    public NamespaceFilter(String namespaceUri,
            boolean addNamespace) {
        super();

        if (addNamespace)
            this.usedNamespaceUri = namespaceUri;
        else 
            this.usedNamespaceUri = "";
        this.addNamespace = addNamespace;
    }



    @Override
    public void startDocument() throws SAXException {
        super.startDocument();
        if (addNamespace) {
            startControlledPrefixMapping();
        }
    }



    @Override
    public void startElement(String arg0, String arg1, String arg2,
            Attributes arg3) throws SAXException {

        super.startElement(this.usedNamespaceUri, arg1, arg2, arg3);
    }

    @Override
    public void endElement(String arg0, String arg1, String arg2)
            throws SAXException {

        super.endElement(this.usedNamespaceUri, arg1, arg2);
    }

    @Override
    public void startPrefixMapping(String prefix, String url)
            throws SAXException {


        if (addNamespace) {
            this.startControlledPrefixMapping();
        } else {
            //Remove the namespace, i.e. don′t call startPrefixMapping for parent!
        }

    }

    private void startControlledPrefixMapping() throws SAXException {

        if (this.addNamespace && !this.addedNamespace) {
            //We should add namespace since it is set and has not yet been done.
            super.startPrefixMapping("", this.usedNamespaceUri);

            //Make sure we dont do it twice
            this.addedNamespace = true;
        }
    }

}

This filter is designed to both be able to add the namespace if it is not present:

如果命名空间不存在，此过滤器设计为能够添加命名空间：

new NamespaceFilter("http://www.example.com/namespaceurl", true);

and to remove any present namespace:

并删除任何现有的命名空间：

new NamespaceFilter(null, false);

The filter can be used during parsing as follows:

可以在解析过程中使用过滤器，如下所示：

//Prepare JAXB objects
JAXBContext jc = JAXBContext.newInstance("jaxb.package");
Unmarshaller u = jc.createUnmarshaller();

//Create an XMLReader to use with our filter
XMLReader reader = XMLReaderFactory.createXMLReader();

//Create the filter (to add namespace) and set the xmlReader as its parent.
NamespaceFilter inFilter = new NamespaceFilter("http://www.example.com/namespaceurl", true);
inFilter.setParent(reader);

//Prepare the input, in this case a java.io.File (output)
InputSource is = new InputSource(new FileInputStream(output));

//Create a SAXSource specifying the filter
SAXSource source = new SAXSource(inFilter, is);

//Do unmarshalling
Object myJaxbObject = u.unmarshal(source);

To use this filter to output XML from a JAXB object, have a look at the code below.

要使用此过滤器从 JAXB 对象输出 XML，请查看下面的代码。

//Prepare JAXB objects
JAXBContext jc = JAXBContext.newInstance("jaxb.package");
Marshaller m = jc.createMarshaller();

//Define an output file
File output = new File("test.xml");

//Create a filter that will remove the xmlns attribute      
NamespaceFilter outFilter = new NamespaceFilter(null, false);

//Do some formatting, this is obviously optional and may effect performance
OutputFormat format = new OutputFormat();
format.setIndent(true);
format.setNewlines(true);

//Create a new org.dom4j.io.XMLWriter that will serve as the 
//ContentHandler for our filter.
XMLWriter writer = new XMLWriter(new FileOutputStream(output), format);

//Attach the writer to the filter       
outFilter.setContentHandler(writer);

//Tell JAXB to marshall to the filter which in turn will call the writer
m.marshal(myJaxbObject, outFilter);

This will hopefully help someone since I spent a day doing this and almost gave up twice ;)

这将有望帮助某人，因为我花了一天时间这样做并且几乎放弃了两次；）

回答by Henrique

In my situation, I have many namespaces and after some debug I find another solution just changing the NamespaceFitler class. For my situation (just unmarshall) this work fine.

在我的情况下，我有很多命名空间，经过一些调试后，我找到了另一个解决方案，只是更改 NamespaceFitler 类。对于我的情况（只是解组），这个工作正常。

 import javax.xml.namespace.QName;
 import org.xml.sax.Attributes;
 import org.xml.sax.ContentHandler;
 import org.xml.sax.SAXException;
 import org.xml.sax.helpers.XMLFilterImpl;
 import com.sun.xml.bind.v2.runtime.unmarshaller.SAXConnector;

 public class NamespaceFilter extends XMLFilterImpl {
    private SAXConnector saxConnector;

    @Override
    public void startElement(String uri, String localName, String qName, Attributes atts) throws SAXException {
        if(saxConnector != null) {
            Collection<QName> expected = saxConnector.getContext().getCurrentExpectedElements();
            for(QName expectedQname : expected) {
                if(localName.equals(expectedQname.getLocalPart())) {
                    super.startElement(expectedQname.getNamespaceURI(), localName, qName, atts);
                    return;
                }
            }
        }
        super.startElement(uri, localName, qName, atts);
    }

    @Override
    public void setContentHandler(ContentHandler handler) {
        super.setContentHandler(handler);
        if(handler instanceof SAXConnector) {
            saxConnector = (SAXConnector) handler;
        }
    }
}

回答by lunicon

I have encoding problems with XMLFilter solution, so I made XMLStreamReader to ignore namespaces:

我有 XMLFilter 解决方案的编码问题，所以我让 XMLStreamReader 忽略命名空间：

class XMLReaderWithoutNamespace extends StreamReaderDelegate {
    public XMLReaderWithoutNamespace(XMLStreamReader reader) {
      super(reader);
    }
    @Override
    public String getAttributeNamespace(int arg0) {
      return "";
    }
    @Override
    public String getNamespaceURI() {
      return "";
    }
}

InputStream is = new FileInputStream(name);
XMLStreamReader xsr = XMLInputFactory.newFactory().createXMLStreamReader(is);
XMLReaderWithoutNamespace xr = new XMLReaderWithoutNamespace(xsr);
Unmarshaller um = jc.createUnmarshaller();
Object res = um.unmarshal(xr);