使用DOM解析器将树节点填充到XML文档之外的JTree中

Question

我是Java的初学者。 我正在尝试使用DOM解析器从XML文件（在本例中为helloWorld.xml）动态填充JTree。 我从流动的线程那里获得了代码帮助： 使用DOM解析器从XML文档中创建JTree

package java_img_parser.jtrees;

import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

public class XMLTree extends JTree {
DefaultTreeModel dm;
JTree tree = new JTree(dm);

public XMLTree() throws SAXException, IOException {
    this.dm = treeBuilder();
}

public DefaultTreeModel treeBuilder() throws SAXException, IOException{
    Node root = null;
    DefaultTreeModel dtModel = null;
    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
    try {
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document doc = db.parse("helloWorld.xml");
        root = (Node)doc.getDocumentElement();
    } catch (ParserConfigurationException ex) {
        Logger.getLogger(XMLTree.class.getName()).log(Level.SEVERE, null, ex);
    }

    if(root != null){
        dtModel = new DefaultTreeModel(makeTree(root));
        dtModel.reload();
    }
    return dtModel;
}
private DefaultMutableTreeNode makeTree(Node root){
    DefaultMutableTreeNode rootTreeNode;
    rootTreeNode = new DefaultMutableTreeNode(root.getNodeName());
    NodeList nodeList = root.getChildNodes();
    for(int count=0;count<nodeList.getLength();count++){
        Node tempNode = nodeList.item(count);
        if(tempNode.getNodeType() == Node.ELEMENT_NODE){
            if(tempNode.hasChildNodes()){
                rootTreeNode.add(makeTree(tempNode));
            }
        }
    }
    System.out.println("Child-Node of"+root.getParentNode()+"is"+root.getChildNodes());
    return rootTreeNode;

}


public static void main(String args[]) throws SAXException, IOException{
    JFrame myFrame = new JFrame();
    myFrame.setTitle("XmlJTreeExample");
    myFrame.setSize(300, 500);
    myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    myFrame.setLocationRelativeTo(null);

    XMLTree myTree = new XMLTree();
    System.out.println("Height of this JTree is:" + myTree.tree.getHeight());

    myFrame.add(myTree.tree);
    myFrame.setVisible(true);

    }
}

当我执行println（）时，我可以看到正在遍历子节点。 但是相同的节点没有被添加到我的JTree中（它显示零（0）高度）。

我的源XML文件与上述线程中的文件相同：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE people SYSTEM "validator.dtd">

<people>
    <student>
        <name>John</name>
        <course>Computer Technology</course>
        <semester>6</semester>
        <scheme>E</scheme>
    </student>

    <student>
        <name>Foo</name>
        <course>Industrial Electronics</course>
        <semester>6</semester>
        <scheme>E</scheme>
    </student>
</people>

我得到的输出是一个空白的JFrame，并在输出控制台中运行：

Child-Node of[student: null]is[name: null]
Child-Node of[student: null]is[course: null]
Child-Node of[student: null]is[semester: null]
Child-Node of[student: null]is[scheme: null]
Child-Node of[people: null]is[student: null]
Child-Node of[student: null]is[name: null]
Child-Node of[student: null]is[course: null]
Child-Node of[student: null]is[semester: null]
Child-Node of[student: null]is[scheme: null]
Child-Node of[people: null]is[student: null]
Child-Node of[#document: null]is[people: null]
Height of this JTree is:0
BUILD SUCCESSFUL (total time: 23 seconds)

Answer 1

摇摆围绕模型，模型为王。 基本上，您想根据要构造的结构将XML的内容加载到TreeModel 。

加载模型后，将其应用于JTree的实例

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.io.IOException;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
import javax.swing.tree.TreePath;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

public class TestTree {

    public static void main(String[] args) {
        new TestTree();
    }

    public TestTree() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                DefaultMutableTreeNode root = new DefaultMutableTreeNode("People");
                DefaultTreeModel model = new DefaultTreeModel(root);
                loadXMLDocument(root);

                JTree tree = new JTree(model);
                tree.setRootVisible(false);
                tree.setShowsRootHandles(true);
                tree.expandPath(new TreePath(root));

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new JScrollPane(tree));
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }

        });
    }

    protected Node getNodeFrom(Node node, String query) throws XPathExpressionException {

        XPath xPath = XPathFactory.newInstance().newXPath();
        XPathExpression xExpress = xPath.compile(query);
        return (Node)xExpress.evaluate(node, XPathConstants.NODE);

    }

    protected NodeList getNodesFrom(Node node, String query) throws XPathExpressionException {

        XPath xPath = XPathFactory.newInstance().newXPath();
        XPathExpression xExpress = xPath.compile(query);
        return (NodeList)xExpress.evaluate(node, XPathConstants.NODESET);

    }

    protected void loadXMLDocument(DefaultMutableTreeNode parent) {

        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        try {
            DocumentBuilder db = dbf.newDocumentBuilder();
            Document doc = db.parse(getClass().getResourceAsStream("/People.xml"));
            Node root = (Node) doc.getDocumentElement();

            NodeList students = getNodesFrom(root, "/people/student");
            for (int index = 0; index < students.getLength(); index++) {

                Node studentNode = students.item(index);
                DefaultMutableTreeNode studentTreeNode = new DefaultMutableTreeNode("Student");
                Node name = getNodeFrom(studentNode, "name");
                Node course = getNodeFrom(studentNode, "course");
                Node semester = getNodeFrom(studentNode, "semester");
                Node scheme = getNodeFrom(studentNode, "scheme");

                studentTreeNode.setUserObject(name.getTextContent());
                studentTreeNode.add(new DefaultMutableTreeNode("Course: " + course.getTextContent()));
                studentTreeNode.add(new DefaultMutableTreeNode("Semester: " + semester.getTextContent()));
                studentTreeNode.add(new DefaultMutableTreeNode("Scheme: " + scheme.getTextContent()));

                parent.add(studentTreeNode);

            }

        } catch (ParserConfigurationException | SAXException | IOException | XPathExpressionException ex) {
            ex.printStackTrace();
        }

    }

    public class TestPane extends JPanel {

        public TestPane() {
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.dispose();
        }

    }

}

详细了解如何使用树木