大文件断点下载

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        if (Environment.getExternalStorageState().equals(
                Environment.MEDIA_MOUNTED)) {
            File file = Environment.getExternalStorageDirectory();
            Log.i(TAG, "begin download:" + file.getPath());
            testDownload(file.getPath());
        }
    }

 private void testDownload(String filepath) {
  long breakPoint = 0;
  try {
   String localPath = filepath + "/oracle10g.zip";
   Log.i(TAG, "begin download:" + localPath);
   
   File file = new File(localPath);
   
   if (file.exists()) {
    breakPoint = file.length();  
    Log.d(TAG, "breakPoint:" + breakPoint);
   }
   String targetURL = "http://10.1.31.231:8080/Message/oracle10g.zip";
   URL url = new URL(targetURL);
   HttpURLConnection httpConnection = (HttpURLConnection) url
     .openConnection();
   
   //判断是否已经下载完毕
   Map<String, List<String>> map = httpConnection.getHeaderFields();
   Iterator<?>  iter = map.entrySet().iterator(); 
   while (iter.hasNext()) { 
       Map.Entry entry = (Map.Entry) iter.next(); 
       String key = (String) entry.getKey(); 
       List<String> list = (List<String>) entry.getValue(); 
       Log.i(TAG, "\r\nkey=" + key);
       for(String s : list) {
         Log.d(TAG, "value = " + s);
       }
   } 
   if (breakPoint == Integer.parseInt( map.get("content-length").get(0) )) {
    Log.d(TAG, "已经下载完毕!");
    return;
   }
   
   // 下面告诉服务器从breakPoint开始发送过来，而不需要重头(第0字节)发送.
   httpConnection.setRequestProperty("RANGE", "bytes=" + breakPoint
     + "-");
   RandomAccessFile localFile = new RandomAccessFile(file, "rw");
   localFile.seek(breakPoint); // 跳到断点处再继续写文件...
 
   
   InputStream inputStream = httpConnection.getInputStream();
   byte[] bytes = new byte[2048];
   int currentRead = 0;
   while ((currentRead = inputStream.read(bytes, 0, 2048 - 1)) > 0)
   {
    localFile.write(bytes, 0, currentRead);
   }
  } catch (Exception e) {
   Log.e(TAG, e.toString());
   e.printStackTrace();
  }
 }