Why is drag and drop taking time on huge files?

Question

I created a java program that works by accepting a file that got dragged and dropped. When ever i drag small files, it works. but when i drag huge file 100MB above, it hangs till it finish processing the file. I'm using Macbook with macOS High Sierra.

public ArrayList result() {

    TransferHandler th;
    th = new TransferHandler() {
        @Override
        public boolean canImport(JComponent comp, DataFlavor[] transfarFlavors) {
            return true;
        }

        @Override
        public boolean importData(JComponent comp, Transferable t) {

            try {
                List<File> files = (List<File>) t.getTransferData(DataFlavor.javaFileListFlavor);
                files.forEach((File file) -> {
                    String fName = file.getName();
                    String fPath = file.getAbsolutePath();
//I even added animation to show when the file is dropped, since small files are executed fast the animation doesn't show, but large files hang so no animation too.
                    ImageIcon loadPage = new ImageIcon(new ImageIcon("/Users/me/Pictures/hit.gif").getImage());
                    loadingImage.setIcon(loadPage);
                    Processor starts = new Processor();
                    try {
                        result = starts.getFile(fPath, fName);
                        setResult(result());

                        //fileNameText.setOpaque(true);
                    } catch (IOException ex) {
                        Logger.getLogger(DragnDrop.class.getName()).log(Level.SEVERE, null, ex);
                    } catch (InterruptedException ex) {
                        Logger.getLogger(DragnDrop.class.getName()).log(Level.SEVERE, null, ex);
                    }
                });
            } catch (UnsupportedFlavorException | IOException ex) {
                Logger.getLogger(DragnDrop.class.getName()).log(Level.SEVERE, null, ex);
            }
            return true;
        }
    };
    DnD.setTransferHandler(th);

    return result;
}

Answer 1

To solve the problem with the blocked EDT you can use a javax.swing.SwingWorker.

Your code is very vague about what the result of Processor.getFile() is and what happens with that result and therefore I can only make rudimentary suggestions about the result processing in the SwingWorker.

public ArrayList<Object> result() {

    TransferHandler th;
    th = new TransferHandler() {
        @Override
        public boolean canImport(JComponent comp, DataFlavor[] transfarFlavors) {
            return true;
        }

        @Override
        public boolean importData(JComponent comp, Transferable t) {

            try {
                ImageIcon loadPage = new ImageIcon(new ImageIcon("/Users/me/Pictures/hit.gif").getImage());
                loadingImage.setIcon(loadPage);
                List<File> files = (List<File>) t.getTransferData(DataFlavor.javaFileListFlavor);
                FileWorker fw = new FileWorker(files);
                fw.execute();
            } catch (UnsupportedFlavorException | IOException ex) {
                Logger.getLogger(DragnDrop.class.getName()).log(Level.SEVERE, null, ex);
            }
            return true;
        }
    };
    DnD.setTransferHandler(th);

    return null;
}

private static class FileWorker extends SwingWorker<Object, Object> {

    private final List<File> files;
    public FileWorker(List<File> files) {
        this.files = files;
    }

    @Override
    protected List<Object> doInBackground() throws Exception {
        List<Object> results = new ArrayList<>();
        files.forEach((File file) -> {
            String fName = file.getName();
            String fPath = file.getAbsolutePath();
            Processor starts = new Processor();
            try {
                Object result = starts.getFile(fPath, fName);
                results.add(result);
                publish(result);

            } catch (IOException | InterruptedException ex) {
                Logger.getLogger(DragnDrop.class.getName()).log(Level.SEVERE, null, ex);
            }
        });
        return results;
    }

    @Override
    protected void process(List<Object> chunks) {
        // here you could update UI elements with some intermediate results
    }

    @Override
    protected void done() {
        // here you could update UI elements with the final results
    }
}