code: static String downloadFile(String artifactUrl, String checksum) {
          LOGGER.entering(new Object[] { artifactUrl, checksum });
          Preconditions.checkArgument(StringUtils.isNotBlank(artifactUrl), "Invalid URL: Cannot be null or empty");
          Preconditions.checkArgument(StringUtils.isNotBlank(checksum), "Invalid CheckSum: Cannot be null or empty");
          // Making sure only the files supported go through the download and extraction.
          isValidFileType(artifactUrl);
          String algorithm = null;
          if (isValidSHA1(checksum)) {
              algorithm = "SHA1";
          } else if (isValidMD5(checksum)) {
              algorithm = "MD5";
          }
          String result = downloadFile(artifactUrl, checksum, algorithm);
          LOGGER.exiting(result);
          return result;
      }
docs: Download a file from the specified url
  
  @param artifactUrl
  url of the file to be downloaded.
  @param checksum
  checksum to downloaded file.
  @return the downloaded file path.