public Builder mergeAwsS3DataSource(
          com.google.storagetransfer.v1.proto.TransferTypes.AwsS3Data value) {
        if (awsS3DataSourceBuilder_ == null) {
          if (dataSourceCase_ == 2
              && dataSource_
                  != com.google.storagetransfer.v1.proto.TransferTypes.AwsS3Data
                      .getDefaultInstance()) {
            dataSource_ =
                com.google.storagetransfer.v1.proto.TransferTypes.AwsS3Data.newBuilder(
                        (com.google.storagetransfer.v1.proto.TransferTypes.AwsS3Data) dataSource_)
                    .mergeFrom(value)
                    .buildPartial();
          } else {
            dataSource_ = value;
          }
          onChanged();
        } else {
          if (dataSourceCase_ == 2) {
            awsS3DataSourceBuilder_.mergeFrom(value);
          } else {
            awsS3DataSourceBuilder_.setMessage(value);
          }
        }
        dataSourceCase_ = 2;
        return this;
      }
<pre>
An AWS S3 data source.
</pre>

<code>.google.storagetransfer.v1.AwsS3Data aws_s3_data_source = 2;</code>
java-storage-transfer/proto-google-cloud-storage-transfer-v1/src/main/java/com/google/storagetransfer/v1/proto/TransferTypes.java