private com.google.protobuf.SingleFieldBuilderV3<
              com.google.storagetransfer.v1.proto.TransferTypes.AwsS3Data,
              com.google.storagetransfer.v1.proto.TransferTypes.AwsS3Data.Builder,
              com.google.storagetransfer.v1.proto.TransferTypes.AwsS3DataOrBuilder>
          getAwsS3DataSourceFieldBuilder() {
        if (awsS3DataSourceBuilder_ == null) {
          if (!(dataSourceCase_ == 2)) {
            dataSource_ =
                com.google.storagetransfer.v1.proto.TransferTypes.AwsS3Data.getDefaultInstance();
          }
          awsS3DataSourceBuilder_ =
              new com.google.protobuf.SingleFieldBuilderV3<
                  com.google.storagetransfer.v1.proto.TransferTypes.AwsS3Data,
                  com.google.storagetransfer.v1.proto.TransferTypes.AwsS3Data.Builder,
                  com.google.storagetransfer.v1.proto.TransferTypes.AwsS3DataOrBuilder>(
                  (com.google.storagetransfer.v1.proto.TransferTypes.AwsS3Data) dataSource_,
                  getParentForChildren(),
                  isClean());
          dataSource_ = null;
        }
        dataSourceCase_ = 2;
        onChanged();
        return awsS3DataSourceBuilder_;
      }
<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