How to check if a download process is complete

Question

My application will parse a XML file from my web server then download the files. My application will get the contents of "URL" from in XML file and download it using Common-IO's FileUtils. My problem is, how do I know that my download process is done or not. There is a lot of "URL" in my XML file.

Here is some part of my code:

private Proxy proxy = Proxy.NO_PROXY;
    public void downloadLibrary()
        {
            System.out.println("Start downloading libraries from server...");
            try
            {
                URL resourceUrl = new URL("http://www.example.com/libraries.xml");
                DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
                DocumentBuilder db = dbf.newDocumentBuilder();
                Document doc = db.parse(resourceUrl.openConnection(proxy).getInputStream());
                NodeList nodeLst = doc.getElementsByTagName("Contents");
                for (int i = 0; i < nodeLst.getLength(); i++)
                {
                    Node node = nodeLst.item(i);

                    if (node.getNodeType() == 1)
                    {
                        Element element = (Element)node;
                        String key = element.getElementsByTagName("Key").item(0).getChildNodes().item(0).getNodeValue();
                        File f = new File(launcher.getWorkingDirectory(), key);
                        downloadFile("http://www.example.com/" + key, f, "libraries");
                    }
                }
            }
            catch(Exception e)
            {
                System.out.println("Error was found when trying to download libraries file " + e);
            }

        }

        public void downloadFile(final String url, final File path, final String fileName)
        {
            SwingWorker<Void, Void> worker = new SwingWorker<Void, Void>()
            {
                @Override
                protected Void doInBackground() throws Exception
                {
                    launcher.println("Downloading file " + fileName + "...");
                    try
                    {
                        URL fileURL = new URL(url);
                        ReadableByteChannel rbc = Channels.newChannel(fileURL.openStream());
                        FileOutputStream fos = new FileOutputStream(path);
                        fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
                    }
                    catch(Exception e)
                    {
                        System.out.println("Cannot download file : " + fileName + " " + e);
                    }
                    return null;
                }
                @Override
                public void done()
                {
                    System.out.println(fileName + " had downloaded sucessfully");

                }
            };
            worker.execute();
        }

Answer 1

If you send each download with one thread, which I recomend, You have severals possibilities.

Use of Future and FutureTask to wait until all the threads are done.

To use thread.join() to wait until the thread stops.