Swing/FileAndTextTransferHandler のバックアップ(No.4)

public void addTab(File file) {
  JTextArea textArea = new JTextArea();
  textArea.setDragEnabled(true);
  new DropTarget(textArea, DnDConstants.ACTION_COPY,
                 new FileDropTargetListener(), true);
  if (file != null) {
    try (Reader in = Files.newBufferedReader(file.toPath(), StandardCharsets.UTF_8)) {
      textArea.read(in, "File");
      tabbedPane.addTab(file.getName(), new JScrollPane(textArea));
    } catch (IOException ex) {
      UIManager.getLookAndFeel().provideErrorFeedback(textArea);
    }
  } else {
    tabbedPane.addTab("*untitled*", new JScrollPane(textArea));
  }
  tabbedPane.setSelectedIndex(tabbedPane.getTabCount() - 1);
}

public void addFile(Transferable transferable)
      throws UnsupportedFlavorException, IOException {
  List<?> list = (List<?>) transferable.getTransferData(
      DataFlavor.javaFileListFlavor);
  new SwingWorker<Void, Void>() {
    @Override protected Void doInBackground() {
      for (Object o : list) {
        if (o instanceof File) {
          addTab((File) o);
        }
      }
      return null;
    }
  }.execute();
}

private class FileDropTargetListener extends DropTargetAdapter {
  @Override public void drop(DropTargetDropEvent e) {
    Transferable transferable = e.getTransferable();
    if (e.isDataFlavorSupported(DataFlavor.javaFileListFlavor)) {
      e.acceptDrop(DnDConstants.ACTION_COPY);
      try {
        addFile(transferable);
        e.dropComplete(true);
      } catch (UnsupportedFlavorException | IOException ex) {
        e.dropComplete(false);
      }
    } else {
      JTextComponent textArea = (JTextComponent) e.getSource();
      TransferHandler textHandler = textArea.getTransferHandler();
      if (textHandler != null) {
        textHandler.importData(textArea, transferable);
      }
    }
  }
}

private class FileTransferHandler extends TransferHandler {
  @Override public boolean canImport(TransferSupport support) {
    boolean isDrop = support.isDrop();
    boolean supported = support.isDataFlavorSupported(
        DataFlavor.javaFileListFlavor);
    return supported && isDrop;
  }

  @Override public boolean importData(TransferSupport support) {
    Transferable transferable = support.getTransferable();
    try {
      addFile(transferable);
      return true;
    } catch (IOException | UnsupportedFlavorException ex) {
      return false;
    }
  }
}