How can I add dynamically (from a list) nodes to my parent nodes in java jtree?

Question

I asked this question before, but I feel like I didn't give too much of code to explain my problem well enough.

This is what I want to do:

I have a list of objects called User. Each object contains two fields - username and password. I created a method to build a jtree with usernames like this:

public class UserTreeBuilder implements TreeWillExpandListener {
    private JTree userTree;
    DefaultMutableTreeNode dummyParent;

    public JTree build(List<User> list){
        DefaultMutableTreeNode top = new DefaultMutableTreeNode("");
        createNodes(top, list);
        userTree = new JTree(top);
        userTree.getSelectionModel().setSelectionMode
            (TreeSelectionModel.SINGLE_TREE_SELECTION);
        userTree.setRootVisible(false);
        userTree.addTreeWillExpandListener(this);

        return userTree;
    }

    public void createNodes(DefaultMutableTreeNode top, List<User> list) {
        DefaultMutableTreeNode category = null;
        DefaultMutableTreeNode user = null;

        category = new DefaultMutableTreeNode("User");
        top.add(category);


        for(User ui : list){
            user = new DefaultMutableTreeNode(ui.getUserName());
            category.add(user);
        }
    }

    @Override
    public void treeWillExpand(TreeExpansionEvent event) throws ExpandVetoException {
        DefaultMutableTreeNode node = (DefaultMutableTreeNode) userTree.getLastSelectedPathComponent();

        String nodeName = node.toString();
        System.out.println("NODE TO STRING: "+nodeName);

        if (node == null)
            //Nothing is selected.      
        return;

    }

    @Override
    public void treeWillCollapse(TreeExpansionEvent event) throws ExpandVetoException {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

It works good, I see the list as:

(folder icon) users
    (dot icon) user1
    (dot icon) user2
    (dot icon) user3
    etc.

So the accounts user1, user2, etc. are the lowest nodes.

I have a method that gets the username as a parameter and returns a list of things that belongs to this user. It looks like this:

public ArrayList<Things> fetchThings(User user){
    List<Things> list = new ArrayList<Things>();
   .
   .
   .
return list;

My question is - how can I fetch things for a specific user (invoke my method fetchThings) when someone clicks the given user on my original jtree and then display those things as children nodes assigned to that user?

For example, someone clicks user2 and this is what he sees:

(folder icon) users
    (folder icon) user1
    (folder icon) user2
        (dot icon) thing1
        (dot icon) thing2
        (dot icon) thing3
        .
        .
        .
    (folder icon) user3
  etc.

I tried to use lazy loading of children from this page https://docs.oracle.com/javase/tutorial/uiswing/components/tree.html but I cannot make it work. Can you please help me with my implementation?

Answer 1

If you had read the JTree JavaDocs you would know that you can get the node that was clicked by using something like...

MouseListener ml = new MouseAdapter() {
     public void mousePressed(MouseEvent e) {
         int selRow = tree.getRowForLocation(e.getX(), e.getY());
         TreePath selPath = tree.getPathForLocation(e.getX(), e.getY());
         if(selRow != -1) {
             if(e.getClickCount() == 1) {
                 mySingleClick(selRow, selPath);
             }
             else if(e.getClickCount() == 2) {
                 myDoubleClick(selRow, selPath);
             }
         }
     }
 };

You can use the TreePath to getLastPathComponent which will return an Object, which in your case, you can cast it to a DefaultMutableTreeNode

If you had read the JavaDocs for TreeWillExpandListener, TreeeExpansionEvent and TreePath, you will know that when treeWillExpand is called, you can get the node which will be expanded by using TreeExpansionEvent#getPath#getLastPathComponent, something like...

@Override
public void treeWillExpand(TreeExpansionEvent event) throws ExpandVetoException {
    DefaultMutableTreeNode treeNode = (DefaultMutableTreeNode) event.getPath().getLastPathComponent();
    System.out.println(treeNode);
}

From there you can simply call whatever functionality you need to in order to obtain the information you need to populate the DefaultMutableTreeNode in question

Your user DefaultMutableTreeNode will need to override the isLeaf method and return false, this will allow the node to be "expandable", something like...

for (User ui : list) {
    user = new DefaultMutableTreeNode(ui.getUserName()) {
        @Override
        public boolean isLeaf() {
            return false;
        }
    };
    category.add(user);
}