code: public synchronized void initialize(URI uri, org.apache.hadoop.conf.Configuration conf,
        @Nullable AlluxioConfiguration alluxioConfiguration)
        throws IOException {
      Preconditions.checkArgument(uri.getScheme().equals(getScheme()),
          PreconditionMessage.URI_SCHEME_MISMATCH.toString(), uri.getScheme(), getScheme());
  
      super.initialize(uri, conf);
      LOG.debug("initialize({}, {}). Connecting to Alluxio", uri, conf);
      HadoopUtils.addSwiftCredentials(conf);
      setConf(conf);
  
      // HDFS doesn't allow the authority to be empty; it must be "/" instead.
      String authority = uri.getAuthority() == null ? "/" : uri.getAuthority();
      mAlluxioHeader = getScheme() + "://" + authority;
      // Set the statistics member. Use mStatistics instead of the parent class's variable.
      mStatistics = statistics;
  
      Authority auth = Authority.fromString(uri.getAuthority());
      if (auth instanceof UnknownAuthority) {
        throw new IOException(String.format("Authority \"%s\" is unknown. The client can not be "
                + "configured with the authority from %s", auth, uri));
      }
  
      mUri = URI.create(mAlluxioHeader);
  
      if (mFileSystem != null) {
        return;
      }
  
      Map<String, Object> uriConfProperties = getConfigurationFromUri(uri);
  
      AlluxioProperties alluxioProps =
          (alluxioConfiguration != null) ? alluxioConfiguration.copyProperties()
              : ConfigurationUtils.defaults();
      AlluxioConfiguration alluxioConf = mergeConfigurations(uriConfProperties, conf, alluxioProps);
      Subject subject = getHadoopSubject();
      if (subject != null) {
        LOG.debug("Using Hadoop subject: {}", subject);
      } else {
        LOG.debug("No Hadoop subject. Using context without subject.");
      }
  
      LOG.info("Initializing filesystem with connect details {}",
          Factory.getConnectDetails(alluxioConf));
  
      mFileSystem = FileSystem.Factory.create(ClientContext.create(subject, alluxioConf));
    }
docs: Initialize the {@link alluxio.hadoop.FileSystem}.
  @param uri file system Uri
  @param conf hadoop configuration
  @param alluxioConfiguration [optional] alluxio configuration
  @throws IOException