如何在JAXB中设置非命名空间的nil和数据类型属性

严修诚

2023-03-14

问题内容：

我在Scala中使用JAXB，编组代码如下所示：

def marshalToXml(): String = {
  val context = JAXBContext.newInstance(this.getClass())
  val writer = new StringWriter
  context.createMarshaller.marshal(this, writer)
  writer.toString()
}

然后对于我的可为null的元素，我将@XmlElement(nillable = true)按照JAXB编组使用带有null字段的注释。这使我的XML输出如下所示：

<name>Alex Dean</name>
<customerReference xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
<quantity>1</quantity>
<createdAt>2011-05-14T00:00:00+03:00</createdAt>

这是一个很好的开始，但是我真的想为这些领域编组的是：

<name>Alex Dean</name>
<customerReference nil="true"/>
<quantity type="integer">1</quantity>
<createdAt type="datetime">2011-05-14T00:00:00+03:00</createdAt>

换句话说，我想删除名称空间属性和前缀，并为除字符串之外的所有属性添加显式XML数据类型属性。这可能很简单，但是我似乎无法在JAXB文档中找到方法。

任何帮助表示感谢！

问题答案：

您可以将JAXB与StAX解析器一起使用，并执行以下操作：

顾客

域模型中的每个属性都将映射为@XmlElement(nillable=true, type=Object.class)。设置type=Object.class将强制将xsi:type属性写出。

package forum8198945;

import java.util.Date;  
import javax.xml.bind.annotation.*;

@XmlRootElement
public class Customer {

    private String name;
    private Customer customerReference;
    private Integer quantity;
    private Date createdAt;

    @XmlElement(nillable=true, type=Object.class)
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @XmlElement(nillable=true, type=Object.class)
    public Customer getCustomerReference() {
        return customerReference;
    }

    public void setCustomerReference(Customer customerReference) {
        this.customerReference = customerReference;
    }

    @XmlElement(nillable=true, type=Object.class)
    public Integer getQuantity() {
        return quantity;
    }

    public void setQuantity(Integer quantity) {
        this.quantity = quantity;
    }

    @XmlElement(nillable=true, type=Object.class)
    public Date getCreatedAt() {
        return createdAt;
    }

    public void setCreatedAt(Date createdAt) {
        this.createdAt = createdAt;
    }

}

XMLStreamWriterWrapper

我们将为创建一个包装器，以XMLStreamWriter剥离所有我们不想写入XML的信息。

package forum8198945;

import javax.xml.namespace.NamespaceContext;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamWriter;

public class XMLStreamWriterWrapper implements XMLStreamWriter {

    private XMLStreamWriter xmlStreamWriter;

    public XMLStreamWriterWrapper(XMLStreamWriter xmlStreamWriter) {
        this.xmlStreamWriter = xmlStreamWriter;
    }

    public void writeStartElement(String localName) throws XMLStreamException {
        xmlStreamWriter.writeStartElement(localName);
    }

    public void writeStartElement(String namespaceURI, String localName) throws XMLStreamException {
        xmlStreamWriter.writeStartElement(namespaceURI, localName);
    }

    public void writeStartElement(String prefix, String localName, String namespaceURI) throws XMLStreamException {
        xmlStreamWriter.writeStartElement(prefix, localName, namespaceURI);
    }

    public void writeEmptyElement(String namespaceURI, String localName) throws XMLStreamException {
        xmlStreamWriter.writeEmptyElement(namespaceURI, localName);
    }

    public void writeEmptyElement(String prefix, String localName, String namespaceURI) throws XMLStreamException {
        xmlStreamWriter.writeEmptyElement(prefix, localName, namespaceURI);
    }

    public void writeEmptyElement(String localName) throws XMLStreamException {
        xmlStreamWriter.writeEmptyElement(localName);
    }

    public void writeEndElement() throws XMLStreamException {
        xmlStreamWriter.writeEndElement();
    }

    public void writeEndDocument() throws XMLStreamException {
        xmlStreamWriter.writeEndDocument();
    }

    public void close() throws XMLStreamException {
        xmlStreamWriter.close();
    }

    public void flush() throws XMLStreamException {
        xmlStreamWriter.flush();
    }

    public void writeAttribute(String localName, String value) throws XMLStreamException {
        xmlStreamWriter.writeAttribute(localName, value);
    }

    public void writeAttribute(String prefix, String namespaceURI, String localName, String value) throws XMLStreamException {
        if("http://www.w3.org/2001/XMLSchema-instance".equals(namespaceURI)) {
            int colonIndex = value.indexOf(':');
            if(colonIndex > -1) {
                value = value.substring(colonIndex + 1);
            }
            xmlStreamWriter.writeAttribute(localName, value);
        } else {
            xmlStreamWriter.writeAttribute(prefix, namespaceURI, localName, value);
        }
    }

    public void writeAttribute(String namespaceURI, String localName, String value) throws XMLStreamException {
        if("http://www.w3.org/2001/XMLSchema-instance".equals(namespaceURI)) {
            int colonIndex = value.indexOf(':');
            if(colonIndex > -1) {
                value = value.substring(colonIndex + 1);
            }
            xmlStreamWriter.writeAttribute(localName, value);
        } else {
            xmlStreamWriter.writeAttribute(namespaceURI, localName, value);
        }
    }

    public void writeNamespace(String prefix, String namespaceURI) throws XMLStreamException {
        if(!"http://www.w3.org/2001/XMLSchema-instance".equals(namespaceURI) && !"http://www.w3.org/2001/XMLSchema".equals(namespaceURI)) {
            xmlStreamWriter.writeNamespace(prefix, namespaceURI);
        }
    }

    public void writeDefaultNamespace(String namespaceURI) throws XMLStreamException {
        if(!"http://www.w3.org/2001/XMLSchema-instance".equals(namespaceURI)) {
            xmlStreamWriter.writeDefaultNamespace(namespaceURI);
        }
    }

    public void writeComment(String data) throws XMLStreamException {
        // TODO Auto-generated method stub
    }

    public void writeProcessingInstruction(String target) throws XMLStreamException {
        // TODO Auto-generated method stub
    }

    public void writeProcessingInstruction(String target, String data) throws XMLStreamException {
        // TODO Auto-generated method stub
    }

    public void writeCData(String data) throws XMLStreamException {
        // TODO Auto-generated method stub
    }

    public void writeDTD(String dtd) throws XMLStreamException {
        // TODO Auto-generated method stub
    }

    public void writeEntityRef(String name) throws XMLStreamException {
        // TODO Auto-generated method stub
    }

    public void writeStartDocument() throws XMLStreamException {
        xmlStreamWriter.writeStartDocument();
    }

    public void writeStartDocument(String version) throws XMLStreamException {
        xmlStreamWriter.writeStartDocument(version);
    }

    public void writeStartDocument(String encoding, String version) throws XMLStreamException {
        xmlStreamWriter.writeStartDocument(encoding, version);
    }

    public void writeCharacters(String text) throws XMLStreamException {
        xmlStreamWriter.writeCharacters(text);
    }

    public void writeCharacters(char[] text, int start, int len) throws XMLStreamException {
        xmlStreamWriter.writeCharacters(text, start, len);
    }

    public String getPrefix(String uri) throws XMLStreamException {
        return xmlStreamWriter.getPrefix(uri);
    }

    public void setPrefix(String prefix, String uri) throws XMLStreamException {
        xmlStreamWriter.setPrefix(prefix, uri);
    }

    public void setDefaultNamespace(String uri) throws XMLStreamException {
        xmlStreamWriter.setDefaultNamespace(uri);
    }

    public void setNamespaceContext(NamespaceContext context) throws XMLStreamException {
        xmlStreamWriter.setNamespaceContext(context);
    }

    public NamespaceContext getNamespaceContext() {
        return xmlStreamWriter.getNamespaceContext();
    }

    public Object getProperty(String name) throws IllegalArgumentException {
        return xmlStreamWriter.getProperty(name);
    }

}

XMLStreamReaderWrapper

我们需要为此创建一个包装器，XMLStreamReader以添加我们在上剥离的所有内容XMLStreamWriter。XMLStreamReader因为我们可以扩展，所以这样做更容易StreamReaderDelegate。

package forum8198945;

import javax.xml.stream.XMLStreamReader;
import javax.xml.stream.util.StreamReaderDelegate;

public class XMLStreamReaderWrapper extends StreamReaderDelegate {

    public XMLStreamReaderWrapper(XMLStreamReader xmlStreamReader) {
        super(xmlStreamReader);
    }

    @Override
    public String getAttributeNamespace(int index) {
        String attributeName = getAttributeLocalName(index);
        if("type".equals(attributeName) || "nil".equals(attributeName)) {
            return "http://www.w3.org/2001/XMLSchema-instance";
        }
        return super.getAttributeNamespace(index);
    }


}

演示版

以下内容演示了所有内容如何结合在一起：

package forum8198945;

import java.io.StringReader;
import java.io.StringWriter;
import java.util.Date;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLOutputFactory;
import javax.xml.stream.XMLStreamWriter;

public class Demo {

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

        Customer customer = new Customer();
        customer.setName("Alex Dean");
        customer.setCustomerReference(null);
        customer.setQuantity(1);
        customer.setCreatedAt(new Date());

        StringWriter stringWriter = new StringWriter();
        XMLOutputFactory xof = XMLOutputFactory.newFactory();
        XMLStreamWriter xsw = xof.createXMLStreamWriter(stringWriter);
        xsw = new XMLStreamWriterWrapper(xsw);
        Marshaller marshaller = jc.createMarshaller();
        marshaller.marshal(customer, xsw);

        String xml = stringWriter.toString();
        System.out.println(xml);

        XMLInputFactory xif = XMLInputFactory.newFactory();
        xif.createXMLStreamReader(new StringReader(xml));

        printValue(customer.getName());
        printValue(customer.getCustomerReference());
        printValue(customer.getQuantity());
        printValue(customer.getCreatedAt());
    }

    private static void printValue(Object value) {
        System.out.print(value);
        System.out.print(" ");
        if(null != value) {
            System.out.print(value.getClass());
        }
        System.out.println();
    }

}

输出量

<?xml version="1.0"?><customer><createdAt type="dateTime">2011-11-25T13:36:49.095</createdAt><customerReference nil="true"></customerReference><name type="string">Alex Dean</name><quantity type="int">1</quantity></customer>
Alex Dean class java.lang.String
null 
1 class java.lang.Integer
Fri Nov 25 13:36:49 EST 2011 class java.util.Date

如何在JAXB中设置非命名空间的nil和数据类型属性

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