Java - FutureTask不工作？

Question

我正在創建一個Java應用程序。在啓動時，我的應用程序將下載所有必需的文件。我的應用程序將解析XML文件並從XML文件的URL中下載文件。我希望我的應用程序下載文件「一步一步」，所以我使用FutureTask我的問題是，FutureTask不適用於我的應用程序。

這是我的代碼的一部分。

Startup.class

public void startDownloading() 
{ 

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

Downloader.class

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（代碼幾乎相同，唯一的URL是不同的））

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; 
     } 

} 

我的XML文件中有大量的<Key></Key>。我的應用程序可以執行LibrariesDownloader並下載所有庫文件。所有庫文件下載後，我的應用程序就停在那裏。它不會執行RDownloader。

是我的應用程序中的任何代碼錯誤？感謝您的幫助。

Answer 1

就啓動了一個新線程

t.run（）;

它應該是t.start()。線程調度程序調用run()。

你可能要忙/等待環路或LibrariesDownloader

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

超時應該

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

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

executor.execute(resDownloader); 

更妙的是，做與Executors.newSingleThreadExecutor()單一的ThreadPoolExecutor或更強大的Executors.newFixedThreadPool(1)並提交兩其中。第二項任務將排隊。

的代碼片段看起來像

ExecutorService executor = Executors.newFixedThreadPool(1); 
executor.execute(libDownloader); 
executor.execute(resDownloader);