JAXB 从 .xml 文件解组到 jlist

Question

我对编组和解组非常陌生。我需要能够在我的程序中保存和加载 xml 文件。首先，我将 post 我的包装器 class。

import java.util.List;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;


//Class created to wrap the list of pc parts on the right Jlist. 
@XmlRootElement

public class JlistWrapper {
    private List<String> Pcpart;

    @XmlElement(name = "Pcpart")
    public List<String> getPcParts(){
    return Pcpart;
    }
    public void setPcparts(List<String> Pcpart){
        this.Pcpart = Pcpart;
    }
}

现在这是我的 save() 方法：

public static void save(File file) throws Exception{


    for (int i = 0; i < computerParts1.size(); i++){
        save.add((String)computerParts1.getElementAt(i));
    }

    //wrapping Jlist data
    JlistWrapper wrapper = new JlistWrapper();
    wrapper.setPcparts(save);

    JAXBContext c = JAXBContext.newInstance(JlistWrapper.class);
    Marshaller m = c.createMarshaller();
    m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
    m.marshal(wrapper, file);   


}

对于我的保存方法，我最初将最后一行设置为仅将 xml 输出到控制台。但是我不确定如何从那里解组（对此有什么想法吗？）。

m.marshal(wrapper, System.out);

现在终于，我无法正确解组的 load() 方法...

public static void load(File file) throws JAXBException{
    JAXBContext context = JAXBContext.newInstance(JlistWrapper.class);
    Unmarshaller unmar = context.createUnmarshaller();

    //Read XML from file
    JlistWrapper wrapper = (JlistWrapper) unmar.unmarshal(file);
    save.clear();
    save.addAll(wrapper.getPcParts());





}

这是我点击加载按钮时出现的错误：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at com.sun.xml.internal.bind.v2.runtime.reflect.Lister$CollectionLister.addToPack(Unknown Source)
at com.sun.xml.internal.bind.v2.runtime.reflect.Lister$CollectionLister.addToPack(Unknown Source)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.Scope.add(Unknown Source)
at com.sun.xml.internal.bind.v2.runtime.property.ArrayERProperty$ReceiverImpl.receive(Unknown Source)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallingContext.endElement(Unknown Source)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.SAXConnector.endElement(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.endElement(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(Unknown Source)
at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal0(Unknown Source)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal(Unknown Source)
at javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal(Unknown Source)
at javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal(Unknown Source)
at javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal(Unknown Source)
at javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal(Unknown Source)
at com.cooksys.assessment.Window.load(Window.java:236)
at com.cooksys.assessment.Window.actionPerformed(Window.java:149)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.AbstractButton.doClick(Unknown Source)
at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access0(Unknown Source)
at java.awt.EventQueue.run(Unknown Source)
at java.awt.EventQueue.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.run(Unknown Source)
at java.awt.EventQueue.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

如果您还需要回答我的问题，请告诉我。提前致谢！

编辑：我忘了澄清我需要在我的 GUI 中将对象列表解组到 JList。到目前为止，我只能将对象列表从 JList 保存到 xml.

Answer 1

您需要通过初始化字段或在 getter:

中执行惰性初始化来确保 getPcParts 不会 return 为空

@XmlElement(name = "Pcpart")
public List<String> getPcParts(){
  if(Pcpart == null) {
    Pcpart = new ArrayList<String>();
  }
  return Pcpart;
}

JAXB 解组列表的方式有点不寻常 - 它不调用 setter，而是假定 getter return 是一个可以添加到的可变列表. unmarshaller 本质上是

theObj.getPcParts().add(theStringValueFromXml)

对于 XML 中的每个 Pcpart 元素。

JAXB 从 .xml 文件解组到 jlist

JAXB Unmarshalling from .xml file to jlist

java

xml

jaxb