@Override
  public List<String> listDatabases() {
    return metaStore.doAs(
        () -> {
          FileSystem fs = fs();
          FileStatus[] fileStatuses = fs.listStatus(warehouse);
          if (fileStatuses == null || fileStatuses.length == 0) {
            return Lists.newArrayList();
          }
          List<String> databases = Lists.newArrayList();
          for (FileStatus s : fileStatuses) {
            if (!s.isDirectory()) {
              continue;
            }
            databases.add(s.getPath().getName());
          }
          return databases;
        });
  }
Hudi catalog implement in hadoop filesystem.
amoro-format-hudi/src/main/java/org/apache/amoro/formats/hudi/HudiHadoopCatalog.java