public Builder setGcsSource(com.google.cloud.translate.v3.GcsInputSource value) {
        if (gcsSourceBuilder_ == null) {
          if (value == null) {
            throw new NullPointerException();
          }
          source_ = value;
          onChanged();
        } else {
          gcsSourceBuilder_.setMessage(value);
        }
        sourceCase_ = 3;
        return this;
      }
<pre>
Google Cloud Storage file source.
</pre>

<code>.google.cloud.translation.v3.GcsInputSource gcs_source = 3;</code>
java-translate/proto-google-cloud-translate-v3/src/main/java/com/google/cloud/translate/v3/DatasetInputConfig.java