code: public File write(String content, boolean isAppend) throws IORuntimeException {
  		BufferedWriter writer = null;
  		try {
  			writer = getWriter(isAppend);
  			writer.write(content);
  			writer.flush();
  		}catch(IOException e){
  			throw new IORuntimeException(e);
  		}finally {
  			IoUtil.close(writer);
  		}
  		return file;
  	}
docs: 将String写入文件
  
  @param content 写入的内容
  @param isAppend 是否追加
  @return 目标文件
  @throws IORuntimeException IO异常