Question

我是刚刚开始使用JAXB的人，我需要的是将对象写入xml并在某些时候将其读回java

这是我的班级：

public class VSM implements  java.io.Externalizable 
{

     ArrayList<String> termList;                    //Term Dictionary
     ArrayList<String> queryTermList;               //Query list
     ArrayList<ArrayList<Doc>> docLists;                    
     ArrayList<ArrayList<Doc>> queryDocLists;
     double[] docLength;                               //Denominator for doc linearization      
     double queryLength;                               //Denominator for query lineriazation


     HashMap<String, Double> queryDocLenght;        //Vector for holding noramiliase queries  
     HashMap<String, Double> queryDoc;
     String Docs[];                          //List of file names 

     Double scoreCap=0.04;                          //Score cap to reduce the effect of stop words

     public static String fileName = "indexedFiles.txt";
     private static final long serialVersionUID = 7863262235394607247L;
public VSM()
{
//Some constructor code
}
}

这是我用来构造XML文件的方法

public void writeXML(VSM vsm)
      {
          try {

                File file = new File("IndexXmlfile.xml");
                //JAXBElement<VSM> jaxbWrappedHeader =  objectFactory.createHeader(obj);

                JAXBContext jaxbContext = JAXBContext.newInstance(VSM.class);
                Marshaller jaxbMarshaller = jaxbContext.createMarshaller();

                // output pretty printed
                jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);

                jaxbMarshaller.marshal(new JAXBElement<VSM>(new QName("uri","local"), VSM.class, vsm), System.out);

                jaxbMarshaller.marshal(vsm, file);
                jaxbMarshaller.marshal(vsm, System.out);

                  } catch (JAXBException e) {
                e.printStackTrace();
                  }

      }

Altough当我尝试运行代码时，我得到错误：

javax.xml.bind.MarshalException
 - with linked exception:
[com.sun.istack.SAXException2: unable to marshal type "KPT.VSM" as an element because it is missing an @XmlRootElement annotation]
    at com.sun.xml.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:326)
    at com.sun.xml.bind.v2.runtime.MarshallerImpl.marshal(MarshallerImpl.java:251)
    at javax.xml.bind.helpers.AbstractMarshallerImpl.marshal(Unknown Source)
    at KPT.VSM.writeXML(VSM.java:477)
    at KPT.VSM.main(VSM.java:511)
Caused by: com.sun.istack.SAXException2: unable to marshal type "KPT.VSM" as an element because it is missing an @XmlRootElement annotation
    at com.sun.xml.bind.v2.runtime.XMLSerializer.reportError(XMLSerializer.java:249)
    at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeRoot(ClassBeanInfoImpl.java:339)
    at com.sun.xml.bind.v2.runtime.XMLSerializer.childAsRoot(XMLSerializer.java:494)
    at com.sun.xml.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:323)
    ... 4 more

我完全不了解JABX及其所有方法，所以对我来说很难理解这个错误，我尝试用谷歌搜索了一下，发现很多人都得到了这个错误，但仍然觉得很难理解这个问题解决方案在这里..

Answer 1

如果您的课程未使用@XmlRootElement进行注释，那么您需要将其包装在JAXBElement的实例中，就像您为marshal某个操作所做的那样：

jaxbMarshaller.marshal(new JAXBElement<VSM>(new QName("uri","local"), VSM.class, vsm), System.out);

例外情况来自您尝试编组VSM实例的时间：

jaxbMarshaller.marshal(vsm, System.out);

更新

感谢您的回答，这样做只让我创建空的xml文件，但是现在我知道我做错了什么，我试图写作是愚蠢的没有指定年代的xml

JAXB (JSR-222)实施不需要任何注释（请参阅：http://blog.bdoughan.com/2012/07/jaxb-no-annotations-required.html）。添加的最常见注释是@XmlRootElement，但没有它，您可以使用JAXBElement（请参阅：http://blog.bdoughan.com/2012/07/jaxb-and-root-elements.html）。如果您的班级没有公共访问者方法，那么您可能也对@XmlAccessorType(XmlAccessType.FIELD)注释感兴趣（请参阅：http://blog.bdoughan.com/2011/06/using-jaxbs-xmlaccessortype-to.html）。

我尝试使用JAXB将对象编组到xml文件时得到错误“缺少@XmlRootElement注释”

1 个答案:

更新