Java实现多线程文件下载的代码示例

public class DownloadWithRange implements Runnable
  {
    private String urlLocation;

    private String filePath;

    private long start;

    private long end;

    DownloadWithRange(String urlLocation, String filePath, long start, long end)
    {
      this.urlLocation = urlLocation;
      this.filePath = filePath;
      this.start = start;
      this.end = end;
    }

    @Override
    public void run()
    {
      try
      {
        HttpURLConnection conn = getHttp();
        conn.setRequestProperty("Range", "bytes=" + start + "-" + end);

        File file = new File(filePath);
        RandomAccessFile out = null;
        if (file != null)
        {
          out = new RandomAccessFile(file, "rwd");
        }
        out.seek(start);
        InputStream in = conn.getInputStream();
        byte[] b = new byte[1024];
        int len = 0;
        while ((len = in.read(b)) != -1)
        {
          out.write(b, 0, len);
        }
        in.close();
        out.close();
      }
      catch (Exception e)
      {
        e.getMessage();
      }

    }

    public HttpURLConnection getHttp() throws IOException
    {
      URL url = null;
      if (urlLocation != null)
      {
        url = new URL(urlLocation);
      }
      HttpURLConnection conn = (HttpURLConnection) url.openConnection();
      conn.setReadTimeout(5000);
      conn.setRequestMethod("GET");

      return conn;
    }

  }

public class DownloadFileWithThreadPool
{
  public void getFileWithThreadPool(String urlLocation,String filePath, int poolLength) throws IOException
  {
    Executor threadPool = Executors.newFixedThreadPool(poolLength);
    
    long len = getContentLength(urlLocation);
    for(int i=0;i<poolLength;i++)
    {
      long start=i*len/poolLength;
      long end = (i+1)*len/poolLength-1;
      if(i==poolLength-1)
      {
        end =len;
      }
      DownloadWithRange download=new DownloadWithRange(urlLocation, filePath, start, end);
      threadPool.execute(download);
    }
  }

  public static long getContentLength(String urlLocation) throws IOException
  {
    URL url = null;
    if (urlLocation != null)
    {
      url = new URL(urlLocation);
    }
    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
    conn.setReadTimeout(5000);
    conn.setRequestMethod("GET");
    long len = conn.getContentLength();

    return len;
  }