JAXB：如果我只设置一个值，为什么一个值返回null，而设置其他值时为什么返回一个实值？

Question

I have generadet a java class from a xsd schema with JAXB . In the the Main class I have a method called recursiveNodeList(NodeList list) that just takes a node list and iterates through it recursivly to get all values out of it.

Everything works except one thing that I cannot simply understand.

In the code below I have these two lines:

item.setNote("Notetest1");
item.setTitle("Title1");

When I run the code I get this output:

title->#text->Title1
note->#text->Notetest1

If I just use one of the lines, like:

item.setNote("Notetest1");
// item.setTitle("Title1"); /*commented out*/

I get this output:

item->note->null

Why is the note null if I just set that value and not call setTitle() and why does it have a value when I call both setNote and setTitle?

The code in its whole:

public class JavaXML {

    public static void main(String[] args) throws ParserConfigurationException, JAXBException, FileNotFoundException {
        Item item = new Item();

        JAXBContext jaxb = JAXBContext.newInstance(item.getClass().getPackage().getName());        
        Marshaller marshaller = jaxb.createMarshaller();
        item.setNote("Notetest1");
        item.setTitle("Title1");


        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        dbf.setNamespaceAware(true);
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document doc = db.newDocument();
        marshaller.marshal(item, doc);

        NodeList nodeList = doc.getChildNodes();
        recursiveNodeList(nodeList);

    }

    public static void recursiveNodeList(NodeList nodeList) {
        for(int i = 0; i< nodeList.getLength(); i++) {
            Node fstNode = nodeList.item(i);
            if (fstNode.getNodeType() == Node.ELEMENT_NODE) {             
                Element fstElmnt = (Element) fstNode;

                if(fstElmnt.getChildNodes().getLength() > 1) {
                    NodeList fstNmElmntLst = fstElmnt.getChildNodes();
                    recursiveNodeList(fstNmElmntLst);
                } else {
                    NodeList fstNmElmntLst = fstElmnt.getChildNodes();
                    if(((Node)fstNmElmntLst.item(0)) != null)
                        System.out.println(fstNode.getNodeName()+"->"+((Node)fstNmElmntLst.item(0)).getNodeName() + "->"+((Node)fstNmElmntLst.item(0)).getNodeValue());
                }
            }
        }
    }
}

EDIT

Another question: If I instead of setting the title and note, set the category like this:

Category category = new Category();
category.setStringOne("string1");
category.setStringTwo("string2");
item.setCategory(category);

Then the output would be:

item->category->string1string2

Is there any way to get the "string1" and "string2" values into separate variables without using string manipulation techniques?

Answer 1

The error is in your recursiveNodeList method. In the single element case you were hitting the System.out.println line with an Element node, and in the two element case you were hitting the System.out.println line with a Text node. The code below will work, but probably needs cleaned up.

public static void recursiveNodeList(NodeList nodeList) {
    for(int i = 0; i< nodeList.getLength(); i++) {
        Node fstNode = nodeList.item(i);
        if (fstNode.getNodeType() == Node.ELEMENT_NODE) {             
            Element fstElmnt = (Element) fstNode;

            if(fstElmnt.getChildNodes().getLength() > 1) {
                NodeList fstNmElmntLst = fstElmnt.getChildNodes();
                recursiveNodeList(fstNmElmntLst);
            } else {
                NodeList fstNmElmntLst = fstElmnt.getChildNodes();
                Node node = fstNmElmntLst.item(0);
                if(node != null)
                    if(node.getNodeType() == Node.ELEMENT_NODE) {
                        System.out.println(fstNode.getNodeName()+"->"+node.getNodeName() + "->"+((Element)node).getTextContent());
                    } else {
                        System.out.println(fstNode.getNodeName()+"->"+node.getNodeName() + "->"+node.getNodeValue());
                    }
                }
            }
        }
    }
}

---

UPDATE

Your JAXB (JSR-222) implementation is creating the document correctly. The original and updated errors you are seeing are due to the way you are processing the DOM nodes in recursiveNodeList. If you are interested in continuing with that approach I would recommend stepping through the code and paying attention to when the current node corresponds to a tag (ie note ) and is of type Element, and when it corresponds to text (ie Notetest1 ) and is of type Text. Below I have given a new code example that uses XPath to introspect the document which you may find easier to use.

package forum9698306;

import javax.xml.bind.*;
import javax.xml.parsers.*;
import javax.xml.xpath.*;    
import org.w3c.dom.*;

public class JavaXML {

    public static void main(String[] args) throws Exception {
        Item item = new Item();

        JAXBContext jaxb = JAXBContext.newInstance(item.getClass().getPackage().getName());        
        Marshaller marshaller = jaxb.createMarshaller();
        item.setNote("Notetest1");
        item.setTitle("Title1");

        Category category = new Category();
        category.setStringOne("string1");
        category.setStringTwo("string2");
        item.setCategory(category);

        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        dbf.setNamespaceAware(true);
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document doc = db.newDocument();
        marshaller.marshal(item, doc);

        XPathFactory xpf = XPathFactory.newInstance();
        XPath xpath = xpf.newXPath();
        System.out.println(xpath.evaluate("item/note/text()", doc, XPathConstants.STRING));
        System.out.println(xpath.evaluate("item/title/text()", doc, XPathConstants.STRING));
        System.out.println(xpath.evaluate("item/category/stringOne/text()", doc, XPathConstants.STRING));
        System.out.println(xpath.evaluate("item/category/stringTwo/text()", doc, XPathConstants.STRING));
    }

}

Output

Notetest1
Title1
string1
string2