public FileTransfer(String fileName, Long fileSizeLeft){
		this.fileName = fileName;
		this.fileSizeLeft = fileSizeLeft;
		
		this.file = new File(this.fileName,"");
		try{
		if(!this.file.exists()){
			this.file.createNewFile();
		}
		
		this.fileOutputStream = new FileOutputStream(file,true);// 追加模式写文件
		this.fileChannel = fileOutputStream.getChannel();
		
		}catch(Exception e){
			e.printStackTrace();
		}
	}