code: public static void write(InputStream in, int bufferSize) {
  		ServletOutputStream out = null;
  		try {
  			out = getOutputStream();
  			IoUtil.copy(in, out, bufferSize);
  		} catch (IOException e) {
  			throw new RenderException("Error when output to client!", e);
  		} finally {
  			IoUtil.close(out);
  			IoUtil.close(in);
  		}
  	}
docs: 返回数据给客户端
  
  @param in 需要返回客户端的内容