code: public static String encodeDataUri(File imageFile) throws IOException{
          String type = FileKit.getFileExtension(imageFile).toLowerCase();
          if("jpg".equals(type)) {
              type = "jpeg";
          }
          return "data:image/"+type+";base64," + encodeBase64(imageFile);
      }
docs: 生成形如data:image/jpeg;base64,iVBORw0KGgoA……的字符串，将图片文件Data URI化
  
  @param imageFile 图片文件对象
  @return 形如data:image/jpeg;base64,iVBORw0KGgoA……的字符串
  @throws IOException