private com.google.protobuf.SingleFieldBuilderV3<
            com.google.cloud.translate.v3beta1.GcsSource,
            com.google.cloud.translate.v3beta1.GcsSource.Builder,
            com.google.cloud.translate.v3beta1.GcsSourceOrBuilder>
        getGcsSourceFieldBuilder() {
      if (gcsSourceBuilder_ == null) {
        if (!(sourceCase_ == 2)) {
          source_ = com.google.cloud.translate.v3beta1.GcsSource.getDefaultInstance();
        }
        gcsSourceBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.cloud.translate.v3beta1.GcsSource,
                com.google.cloud.translate.v3beta1.GcsSource.Builder,
                com.google.cloud.translate.v3beta1.GcsSourceOrBuilder>(
                (com.google.cloud.translate.v3beta1.GcsSource) source_,
                getParentForChildren(),
                isClean());
        source_ = null;
      }
      sourceCase_ = 2;
      onChanged();
      return gcsSourceBuilder_;
    }
<pre>
Google Cloud Storage location. This must be a single file.
For example: gs://example_bucket/example_file.pdf
</pre>

<code>.google.cloud.translation.v3beta1.GcsSource gcs_source = 2;</code>
java-translate/proto-google-cloud-translate-v3beta1/src/main/java/com/google/cloud/translate/v3beta1/DocumentInputConfig.java