I'm following the example370__MarketPrice__Batch java example.
And I want to know if there's a way to make the service only put in the response certain fields.
You can use View feature which is demonstrated in example360__MarketPrice__View. Using a view, a consumer requests a subset of fields with a single request. Then, the server/service sends only the fields of interest as shown in the figure:
You can set Batch and View in a same request. For more details and example source code, please refer to Elektron Messaging API (Java) - Batch and View features