code: protected void writeToFile(TableMeta tableMeta) throws IOException {
  		File dir = new File(modelOutputDir);
  		if (!dir.exists()) {
  			dir.mkdirs();
  		}
  		
  		String target = modelOutputDir + File.separator + tableMeta.modelName + ".java";
  		
  		File file = new File(target);
  		if (file.exists()) {
  			return ;	// 若 Model 存在，不覆盖
  		}
  		
  		OutputStreamWriter osw = null;
  		try {
  			osw = new OutputStreamWriter(new FileOutputStream(file), "UTF-8");
  			osw.write(tableMeta.modelContent);
  		}
  		finally {
  			if (osw != null) {
  				osw.close();
  			}
  		}
  	}
docs: 若 model 文件存在，则不生成，以免覆盖用户手写的代码