code: public static BufferedImage base64StrToImg(String imgStr) {
          Base64.Decoder decoder = Base64.getDecoder();
          byte[] bytes = decoder.decode(imgStr);
          for (int i = 0; i < bytes.length; i++) {
              if (bytes[i] < 0) {
                  bytes[i] += 256;
              }
          }
          ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
          BufferedImage image = null;
          try {
              image = ImageIO.read(bais);
          } catch (IOException e) {
              throw new RuntimeException(e);
          } finally {
              CommonUtils.closeIOStream(bais, null);
          }
          return image;
      }
docs: 将Base64字符串转化成Image对象
  
  @param imgStr 指定Base64编码的图片字符串
  @return 返回转化后的Image对象, 失败返回Null