使用JAXBContext和Marshaller將對象與XML和XML對象

Question

BufferedWriter out = new BufferedWriter(fstream); 
    try { 
     JAXBContext context = JAXBContext.newInstance(NarociloType.class); 

     Marshaller m = context.createMarshaller(); 
     m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true); 

     m.marshal(parameters, out); 
     out.newLine(); 
    } catch (PropertyException pe) { 
     // TODO: Add catch code 
     pe.printStackTrace(); 
    } catch (JAXBException jaxbe) { 
     // TODO: Add catch code 
     jaxbe.printStackTrace(); 
    } 

但空類型不存儲到XML中。例如：

NarociloType.date = null 

但我不能在xml中看到<date></date>。 JAXB編組不會爲空值創建空元素

我還可以使用JAXBContext更改XML以反對對象嗎？

Answer 1

注：下面的例子中EclipseLink JAXB (MOXy)工作，但包含在Java SE 6

不是JAXB參考實現如果使用莫西爲您的JAXB提供者（我是技術主管） ，那麼你可以在這個用例中使用XmlAdapter。

DateAdatper

import java.util.Date; 

import javax.xml.bind.annotation.XmlValue; 
import javax.xml.bind.annotation.adapters.XmlAdapter; 
import forum235.DateAdapter.AdaptedDate; 

public class DateAdapter extends XmlAdapter<AdaptedDate, Date> { 

    @Override 
    public Date unmarshal(AdaptedDate adaptedDate) throws Exception { 
     return adaptedDate.date; 
    } 

    @Override 
    public AdaptedDate marshal(Date date) throws Exception { 
     AdaptedDate adaptedDate = new AdaptedDate(); 
     adaptedDate.date = date; 
     return adaptedDate; 
    } 

    static class AdaptedDate { 
     @XmlValue 
     public Date date; 
    } 

} 

根

import java.util.Date; 

import javax.xml.bind.annotation.XmlRootElement; 
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter; 

@XmlRootElement 
public class Root { 

    private Date date; 

    @XmlJavaTypeAdapter(DateAdapter.class) 
    public Date getDate() { 
     return date; 
    } 

    public void setDate(Date date) { 
     this.date = date; 
    } 

} 

演示

import java.util.Date; 

import javax.xml.bind.JAXBContext; 
import javax.xml.bind.Marshaller; 

public class Demo { 

    public static void main(String[] args) throws Exception { 
     JAXBContext jc = JAXBContext.newInstance(Root.class); 
     Marshaller marshaller = jc.createMarshaller(); 
     marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true); 

     Root root = new Root(); 
     marshaller.marshal(root, System.out); 

     root.setDate(new Date()); 
     marshaller.marshal(root, System.out); 
    } 

} 

輸出

<?xml version="1.0" encoding="UTF-8"?> 
<root> 
    <date/> 
</root> 
<?xml version="1.0" encoding="UTF-8"?> 
<root> 
    <date>2011-06-16T09:16:09.452</date> 
</root> 

jaxb.properties

您使用莫西爲您的JAXB提供者需要提供一個名爲在同一個包jaxb.properties文件作爲域類具有以下條目：

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory 

有關XmlAdapter更多信息

• http://bdoughan.blogspot.com/2010/07/xmladapter-jaxbs-secret-weapon.html
• http://bdoughan.blogspot.com/2011/05/jaxb-and-joda-time-dates-and-times.html
• http://bdoughan.blogspot.com/2010/12/jaxb-and-immutable-objects.html
• http://bdoughan.blogspot.com/2010/12/represent-string-values-as-element.html

Answer 2

• 您可能會感興趣nillable elements。你可以解組。