code: public void downloadFileUsingRequesterPays(
        String projectId, String bucketName, String srcFilename, Path destFilePath)
        throws IOException {
      // [START storage_download_file_requester_pays]
      // The project ID to bill
      // String projectId = "my-billable-project-id";
  
      // The name of the bucket to access
      // String bucketName = "my-bucket";
  
      // The name of the remote file to download
      // String srcFilename = "file.txt";
  
      // The path to which the file should be downloaded
      // Path destFilePath = Paths.get("/local/path/to/file.txt");
  
      // Instantiate a Google Cloud Storage client
      Storage storage = StorageOptions.getDefaultInstance().getService();
  
      // Get specific file from specified bucket
      Blob blob = storage.get(BlobId.of(bucketName, srcFilename));
  
      // Download file to specified path
      blob.downloadTo(destFilePath, Blob.BlobSourceOption.userProject(projectId));
      // [END storage_download_file_requester_pays]
    }
docs: Example of downloading a file using Requester pay.