// Redacted from constructor where this is being created in the prototype linked below.
serverStreamingCallable =
          new GrpcStorageCallableFactory()
              .createServerStreamingCallable(
                  readObjectTransportSettings,
                  storageClient.getSettings().readObjectSettings(),
                  ClientContext.create(storageClient.getSettings()));

// ....

static final MethodDescriptor<ReadObjectRequest, ReadObjectResponse> readObjectMethodDescriptor =
      MethodDescriptor.<ReadObjectRequest, ReadObjectResponse>newBuilder()
          .setType(MethodDescriptor.MethodType.SERVER_STREAMING)
          .setFullMethodName("google.storage.v2.Storage/ReadObject")
          .setRequestMarshaller(ProtoUtils.marshaller(ReadObjectRequest.getDefaultInstance()))
          .setResponseMarshaller(getObjectMediaResponseMarshaller)
          .build();

  GrpcCallSettings<ReadObjectRequest, ReadObjectResponse> readObjectTransportSettings =
      GrpcCallSettings.<ReadObjectRequest, ReadObjectResponse>newBuilder()
          .setMethodDescriptor(readObjectMethodDescriptor)
          .setParamsExtractor(
              request -> {
                RequestParamsBuilder builder = RequestParamsBuilder.create();
                builder.add(request.getBucket(), "bucket", PathTemplate.create("{bucket=**}"));
                return builder.build();
              })
          .build();