Question

I have this class, which should add a JLabel to a JPanel, but for some reason it isn’t doing that. Why is it not adding the JLabel to the JPanel? This takes place in my SwigWorker class in the done() method

package sscce;

import java.io.IOException;
import java.io.StringReader;
import java.io.StringWriter;
import java.util.ArrayList;
import javax.swing.JLabel;
import javax.swing.SwingWorker;
import javax.swing.UIManager;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.w3c.dom.CharacterData;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

public class sscce extends javax.swing.JFrame{
    protected XML xml = new XML();

    public sscce(){
        initComponents();
        GetNotes getNotes = new GetNotes();
        getNotes.execute();
    }

    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">
    private void initComponents() {

        jScrollPane1 = new javax.swing.JScrollPane();
        notesPanel = new javax.swing.JPanel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        javax.swing.GroupLayout notesPanelLayout = new javax.swing.GroupLayout(notesPanel);
        notesPanel.setLayout(notesPanelLayout);
        notesPanelLayout.setHorizontalGroup(
            notesPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 494, Short.MAX_VALUE)
        );
        notesPanelLayout.setVerticalGroup(
            notesPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 433, Short.MAX_VALUE)
        );

        jScrollPane1.setViewportView(notesPanel);

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 496, Short.MAX_VALUE)
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 435, Short.MAX_VALUE)
        );

        pack();
    }// </editor-fold>

    public static void main(String args[]){
        try{
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        }catch(  ClassNotFoundException | InstantiationException | IllegalAccessException | javax.swing.UnsupportedLookAndFeelException ex){
            java.util.logging.Logger.getLogger(sscce.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }

        java.awt.EventQueue.invokeLater(new Runnable(){
            public void run(){
                new sscce().setVisible(true);
            }
        });
    }
    // Variables declaration - do not modify
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JPanel notesPanel;
    // End of variables declaration

    public class GetNotes extends SwingWorker{

        protected ArrayList<XML> notes;

        @Override
        public void done(){
            System.out.println(notes.size());
            for(XML note : notes){
                String n = note.getNode("notes", "note");
                System.out.println(n);
                JLabel lbl = new JLabel(n);
                lbl.setVisible(true);
                notesPanel.add(lbl);
            }
        }

        @Override
        public String doInBackground(){
            String xmlStr = "<?xml version=\"1.0\"?>"
                    + "<root>"
                    + "    <success>true</success>"
                    + "    <notes>"
                    + "        <note>Note 1</note>"
                    + "    </notes>"
                    + "    <notes>"
                    + "        <note>Note 2</note>"
                    + "    </notes>"
                    + "    <notes>"
                    + "        <note>Note 3</note>"
                    + "    </notes>"
                    + "</root>";
            xml.parse(xmlStr);
            notes = xml.getNodes("root", "notes");
            return null;
        }
    }
}

class XML{

    private Document doc;

    public XML(){
    }

    public void parse(String xml){
        try{
            DocumentBuilder db = DocumentBuilderFactory.newInstance().newDocumentBuilder();
            InputSource is = new InputSource();
            is.setCharacterStream(new StringReader(xml));

            doc = db.parse(is);
        }catch(ParserConfigurationException | SAXException | IOException ex){
            //Logger.getLogger(XML.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    public Document getDoc(){
        return this.doc;
    }

    public ArrayList<XML> getNodes(String root, String name){
        ArrayList<XML> elList = new ArrayList<>();
        NodeList nodes = doc.getElementsByTagName(root);
        for(int i = 0; i < nodes.getLength(); i++){
            Element element = (Element)nodes.item(i);
            NodeList nl = element.getElementsByTagName(name);
            for(int c = 0; c < nl.getLength(); c++){
                Element e = (Element)nl.item(c);
                String xmlStr = this.nodeToString(e);
                XML xml = new XML();
                xml.parse(xmlStr);
                elList.add(xml);
            }
        }
        return elList;
    }

    private String nodeToString(Node node){
        StringWriter sw = new StringWriter();
        try{
            Transformer t = TransformerFactory.newInstance().newTransformer();
            t.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
            t.transform(new DOMSource(node), new StreamResult(sw));
        }catch(TransformerException te){
            System.out.println("nodeToString Transformer Exception");
        }
        return sw.toString();
    }

    public String getNode(String root, String name){
        NodeList nodes = doc.getElementsByTagName(root);
        for(int i = 0; i < nodes.getLength(); i++){
            Element element = (Element)nodes.item(i);

            NodeList n = element.getElementsByTagName(name);
            Element e = (Element)n.item(0);
            return getCharacterDataFromElement(e);
        }
        return "";
    }

    public static String getCharacterDataFromElement(Element e){
        Node child = e.getFirstChild();
        if(child instanceof CharacterData){
            CharacterData cd = (CharacterData)child;
            return cd.getData();
        }
        return "";
    }
}

Answer 1

1- Change the layout manager for the notesPanel. GroupLayout really isn’t meant for hand coding like this. In my test, I used FlowLayout.

//        javax.swing.GroupLayout notesPanelLayout = new javax.swing.GroupLayout(notesPanel);
//        notesPanel.setLayout(notesPanelLayout);
//        notesPanelLayout.setHorizontalGroup(
//                    notesPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
//                .addGap(0, 494, Short.MAX_VALUE));
//        notesPanelLayout.setVerticalGroup(
//                    notesPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
//                .addGap(0, 433, Short.MAX_VALUE));
        notesPanel.setLayout(new FlowLayout());

2- Add a call to JComponent#validate after you’ve finished adding the labels.

System.out.println(notes.size());
for (XML note : notes) {
    String n = note.getNode("notes", "note");
    System.out.println(n);
    JLabel lbl = new JLabel(n);
    lbl.setVisible(true);
    notesPanel.add(lbl);
}
notesPanel.validate();

This should encourage the frame to re-layout it’s child components.