Drag and drop to rearrange nodes in the JTree

• download example.jar
• download src.zip
• repository

Code

class TreeTransferHandler extends TransferHandler {
  private final DataFlavor nodesFlavor = new DataFlavor(
      List.class, "List of TreeNode");

  @Override public int getSourceActions(JComponent c) {
    return c instanceof JTree
        && TreeUtils.canStartDrag((JTree) c) ? COPY_OR_MOVE : NONE;
  }

  @Override protected Transferable createTransferable(JComponent c) {
    Transferable transferable = null;
    if (c instanceof JTree && ((JTree) c).getSelectionPaths() != null) {
      List<MutableTreeNode> copies = new ArrayList<>();
      Arrays.stream(((JTree) c).getSelectionPaths()).forEach(path -> {
        DefaultMutableTreeNode node =
            (DefaultMutableTreeNode) path.getLastPathComponent();
        DefaultMutableTreeNode clone =
            new DefaultMutableTreeNode(node.getUserObject());
        copies.add(TreeUtils.deepCopy(node, clone));
      });
      transferable = new Transferable() {
        @Override public DataFlavor[] getTransferDataFlavors() {
          return new DataFlavor[] {nodesFlavor};
        }

        @Override public boolean isDataFlavorSupported(
            DataFlavor flavor) {
          return Objects.equals(nodesFlavor, flavor);
        }

        @Override public Object getTransferData(DataFlavor flavor)
            throws UnsupportedFlavorException {
          if (isDataFlavorSupported(flavor)) {
            return copies;
          } else {
            throw new UnsupportedFlavorException(flavor);
          }
        }
      };
    }
    return transferable;
  }

  @Override public boolean canImport(TransferSupport support) {
    DropLocation dl = support.getDropLocation();
    Component c = support.getComponent();
    return support.isDrop()
        && support.isDataFlavorSupported(nodesFlavor)
        && c instanceof JTree
        && dl instanceof JTree.DropLocation
        && TreeUtils.canImportDropLocation(
            (JTree) c, (JTree.DropLocation) dl);
  }

  @Override public boolean importData(TransferSupport support) {
    Component c = support.getComponent();
    DropLocation dl = support.getDropLocation();
    Transferable transferable = support.getTransferable();
    return canImport(support)
        && c instanceof JTree
        && dl instanceof JTree.DropLocation
        && insertNode((JTree) c, (JTree.DropLocation) dl, transferable);
  }

  private boolean insertNode(
      JTree tree, JTree.DropLocation dl, Transferable transferable) {
    TreePath path = dl.getPath();
    Object p = path.getLastPathComponent();
    TreeModel m = tree.getModel();
    List<?> nodes = getTransferData(transferable);
    if (p instanceof MutableTreeNode && m instanceof DefaultTreeModel) {
      MutableTreeNode parent = (MutableTreeNode) p;
      DefaultTreeModel model = (DefaultTreeModel) m;
      int childIndex = dl.getChildIndex();
      AtomicInteger index = new AtomicInteger(
          getDropIndex(parent, childIndex));
      nodes.stream()
          .filter(MutableTreeNode.class::isInstance)
          .map(MutableTreeNode.class::cast)
          .forEach(n -> model.insertNodeInto(
               n, parent, index.getAndIncrement()));
    }
    return !nodes.isEmpty();
  }

  private static int getDropIndex(
      MutableTreeNode parent, int childIndex) {
    // Configure for drop mode.
    int index = childIndex; // DropMode.INSERT
    if (childIndex == -1) { // DropMode.ON
      index = parent.getChildCount();
    }
    return index;
  }

  private List<?> getTransferData(Transferable t) {
    List<?> nodes;
    try {
      nodes = (List<?>) t.getTransferData(nodesFlavor);
    } catch (UnsupportedFlavorException | IOException ex) {
      nodes = Collections.emptyList();
    }
    return nodes;
  }

  @Override protected void exportDone(
      JComponent src, Transferable data, int action) {
    if (src instanceof JTree && (action & MOVE) == MOVE) {
      cleanup((JTree) src);
    }
  }

  private void cleanup(JTree tree) {
    DefaultTreeModel model = (DefaultTreeModel) tree.getModel();
    TreePath[] selectionPaths = tree.getSelectionPaths();
    if (selectionPaths != null) {
      for (TreePath path : selectionPaths) {
        model.removeNodeFromParent(
            (MutableTreeNode) path.getLastPathComponent());
      }
    }
  }
}

References

• JTree - drag and drop inside one tree - Java 1.6 (Swing / AWT / SWT forum at Coderanch)
• java - Drag and Drop nodes in JTree - Stack Overflow
• Drag and drop to rearrange nodes in the JTree(Japanese)