docs: public byte[] partsFirstBytes(final long max, final String filenameReg, final String contentTypeReg) throws IOException {
          if (!isMultipart()) return null;
          byte[] tmpfile = null;
          boolean has = false;
          for (MultiPart part : parts()) {
              if (has) continue;//不遍历完后面getParameter可能获取不到值
              has = true;
              if (filenameReg != null && !filenameReg.isEmpty() && !part.getFilename().matches(filenameReg)) continue;
              if (contentTypeReg != null && !contentTypeReg.isEmpty() && !part.getContentType().matches(contentTypeReg)) continue;
              tmpfile = part.getContentBytes(max < 1 ? Long.MAX_VALUE : max);
          }
          return tmpfile;
      }