I am working on creating a RAG application using Spring AI and MongoDB for the vector store.

My current entry point/controller is as follows (based heavily on Spring AI's own docs):

@RestController
public class ChatController {

  private final OllamaChatModel chatModel;
  private final VectorStore vectorStore;
  private static final Logger logger = LoggerFactory.getLogger(ChatController.class);

  @Autowired
  public ChatController(OllamaChatModel chatModel, VectorStore vectorStore) {
    this.chatModel = chatModel;
    this.vectorStore = vectorStore;
  }

  @GetMapping("/ai/generate")
  public Map<String, String> generate(
      @RequestParam(value = "message", defaultValue = "Tell me a joke.") String message) {

    var searchRequest = SearchRequest.builder().topK(3).similarityThreshold(.8).build();

    ChatResponse response =
        ChatClient.builder(chatModel).build().prompt(AppConstants.DEFAULT_SYS_PROMPT)
            .advisors(new QuestionAnswerAdvisor(vectorStore, searchRequest)).user(message).call()
            .chatResponse();
    logger.info("Reponse is {}", response);
    return Map.of("generation", response.getResult().getOutput().getText());
  }


}

The "VectorStore" is not explicitly configured in code (i.e. no customization); it relies merely on the "spring-ai-mongodb-atlas-store-spring-boot-starter" dependency and application properties for DB url, DB name, vector index, etc.

The collection used in the VectorStore has a "url" String property set in the "metadata" Object property. I configured that "metadata.url" is available in the documents that are used in the "before" function of QuestionAnswerAdvisor.

How can I have the model return a link to the source URL it uses as context? For reference, I am trying to recreate something like this: /

I have tried the following:

     ChatClient.builder(chatModel).build().prompt(AppConstants.DEFAULT_SYS_PROMPT)
            .advisors(new QuestionAnswerAdvisor(vectorStore, searchRequest)).user(message).call()
           .entity(ResponseModel.class)

where ResponseModel is a very simple POJO:

public class ResponseModel {
  private String response;
  private String url;

  public String getResponse() {
    return response;
  }

  public void setResponse(String response) {
    this.response = response;
  }

  public String getUrl() {
    return url;
  }

  public void setUrl(String url) {
    this.url = url;
  }

}

but the application was not able to populate the URL with the data (the response property was set correctly).

How can this be implemented in SpringAI? Thanks.