code: public void renderTo(Writer writer) throws BeetlException
  	{
  		ByteWriter_Char byteWriter = new ByteWriter_Char(writer, cf.charset, ctx);
  		this.renderTo(byteWriter);
  
  	}
docs: 获取模板输出的文本,输出到Writer里
  
  @param writer
  @throws BeetlException