code: public Page<Bucket> listBucketsWithSizeAndPrefix(String prefix) {
      // [START listBucketsWithSizeAndPrefix]
      // Include a prefix of bucket-name to reduce search space.
      // For more information read https://cloud.google.com/storage/docs/json_api/v1/buckets/list
      Page<Bucket> buckets =
          storage.list(BucketListOption.pageSize(100), BucketListOption.prefix(prefix));
      for (Bucket bucket : buckets.iterateAll()) {
        // do something with the bucket
      }
      // [END listBucketsWithSizeAndPrefix]
      return buckets;
    }
docs: [VARIABLE "bucket_"]