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我正在创建一个 Java 应用程序。启动时，我的应用程序将下载所有必需的文件。我的应用程序将解析 XML 文件并从 XML 文件的 URL 下载文件。我希望我的应用程序“逐步”下载文件，所以我使用FutureTask我的问题是，FutureTask不适用于我的应用程序。

这是我的代码的一部分。

启动类

public void startDownloading()
{

    Thread t = new Thread(new Runnable()
    {
        public void run()
        {
            downloader.startDownload();
        }
    });
    t.run();
    }
}

下载器类

private LibrariesDownloader ld;
private RDownloader rd;

public Downloader()
{
    this.ld = new LibrariesDownloader(launcher);
    this.rd = new RDownloader(launcher);
}

public void startDownload()
{
    ExecutorService executor = Executors.newFixedThreadPool(2);
    FutureTask<Void> libDownloader = new FutureTask<Void>(ld);
    FutureTask<Void> resDownloader = new FutureTask<Void>(rd);
    executor.execute(libDownloader);
    if(libDownloader.isDone())
    {
        executor.execute(resDownloader);
    }
}

LibrariesDownloader.class(& RDownloader.class(代码几乎一样，只是URL不同))

public class LibrariesDownloader implements Callable<Void>
{
    private Proxy proxy = Proxy.NO_PROXY;

    @Override
    public Void call() throws Exception
    {
        try
        {
            URL resourceUrl = new URL("http://www.exmaple.com/libraries.xml");
            DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
            DocumentBuilder db = dbf.newDocumentBuilder();

            Document doc = db.parse(resourceUrl.openConnection(proxy).getInputStream());

            NodeList nodeLst = doc.getElementsByTagName("Content");
            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();
                    final File path = new File("C://test/", key);
                    final String url = "http://www.exmaple.com/dl/" + key;
                    final String fileName = key;
                    SwingWorker<Void, Void> worker = new SwingWorker<Void, Void>()
                    {
                        @Override
                        protected Void doInBackground() throws Exception
                        {
                            try
                            {
                                URL fileURL = new URL(url);
                                org.apache.commons.io.FileUtils.copyURLToFile(fileURL, path);
                            }
                            catch(Exception e)
                            {

                                URL redownloadURL = new URL("http://www.example.com/dl/" + fileName);
                                File p = new File("C://test/", fileName);
                                org.apache.commons.io.FileUtils.copyURLToFile(redownloadURL, p);
                            }
                            return null;
                        }

                        @Override
                        public void done()
                        {
                            System.out.println(fileName + " had downloaded successfully");
                        }
                    };
                    worker.execute();


                    }
                }
            }
            catch(Exception e)
            {
                launcher.println("An error was found when trying to download libraries file " + e);
            }
            return null;
        }

}

<Key></Key>我的 XML 文件中有很多。我的应用程序可以执行LibrariesDownloader和下载所有库文件。下载完所有库文件后，我的应用程序就停在那里。它不会执行RDownloader。

我的应用程序中有任何代码错误吗？谢谢你帮助我。

4

1 回答 1

1

你开始一个新线程

t.run();

应该是t.start()。线程调度程序调用run().

您可能想要一个忙/等待循环或超时LibrariesDownloader

if(libDownloader.isDone())
    {
        executor.execute(resDownloader);
    }

应该

Future<?> future = executor.submit(libDownloader);

while (!future.isDone()) {
    //bad spin wait
} 

executor.execute(resDownloader);

更好的是，制作一个具有Executors.newSingleThreadExecutor()或更健壮的 ThreadPoolExecutorExecutors.newFixedThreadPool(1)并提交它们。第二个任务将排队。

代码片段看起来像

ExecutorService executor = Executors.newFixedThreadPool(1);
executor.execute(libDownloader);
executor.execute(resDownloader);
于 2013-10-05T07:08:15.170 回答