public String getUrl(String fileId) throws Exception{
		String trackerAddr = getTrackerAddr();
		TrackerClient trackerClient = null;
		String url = null;
		try {
			FastDfsFile fastDfsFile = new FastDfsFile(fileId);
			trackerClient = trackerClientPool.borrowObject(trackerAddr);
			Result<String> result = trackerClient.getDownloadStorageAddr(fastDfsFile.group,fastDfsFile.fileName);
			if(result.getCode()==0){
				String hostPort = getDownloadHostPort(result.getData());
				url = "http://"+hostPort+"/"+fastDfsFile.fileName;
			}
		} catch (Exception e) {
			logger.error(e.getMessage());
			throw e;
		} finally {
			if(trackerClient!=null){
				trackerClientPool.returnObject(trackerAddr, trackerClient);
			}
		}
		return url;
	}