public static File downLoad(String serverPath,String savedPath,ProgressDialog dialog){
		try {
			
			URL url=new URL(serverPath);
			HttpURLConnection _conn=(HttpURLConnection) url.openConnection();
			_conn.setRequestMethod("GET");
			_conn.setConnectTimeout(5000);
			int code=_conn.getResponseCode();
			if(code==200){
				//设置进度条的长度
				dialog.setMax(_conn.getContentLength());
				InputStream is=_conn.getInputStream();
				File _file=new File(savedPath);
				FileOutputStream _FileOutputStream=new FileOutputStream(_file);
				int len=0;
				byte[] buffer= new byte[1024];
				int _total=0;
				while((len=is.read(buffer))!=-1){
					_FileOutputStream.write(buffer, 0,len);
					_total+=len;
					dialog.setProgress(_total);
					Thread.sleep(20);
				}
				_FileOutputStream.flush();
				_FileOutputStream.close();
				is.close();
				return _file;
			}else {
				return null;
			}
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			return null;
		}
		
		
	}

android连接服务器下载文件工具类