Composing one complete object from iterator gRPC/protobuf

When using gRPC streaming or in some other cases, it may be necessary to compose one complete object from several others or from an iterator.

Let’s take a look at an example. We have an iterator, received by gRPC stub:

Iterator<ProtoResult> iterator = stub.yourMethod(yourRequest);

And we want to get one complete ProtoResult object, which will be the union of all ProtoResult objects, received from the iterator. This is done like this:

ProtoResult result = null;
if (iterator != null && iterator.hasNext()) {
  ProtoResult.Builder mergedResultBuilder = ProtoResult.newBuilder();
  while (iterator.hasNext()) {
  result =;

As you can see, the main method name is mergeFrom(), which is called on the builder’s protobuf object. That’s all.

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