Getting values from external API and displaying through another controller

If you don't want to use a database, then your other option is to store the date in memory as follows:

@RestController
public class Controller1 {

    private Service service;

    public Controller1(Service service) {
        this.service = service;
    }

    @GetMapping(value = "/test")
    public List<Object> getdata() {
        return service.getData();
    }
}

Your Controller would rely on a Service to get the data from another API as follows:

@Service
public class Service {

    private List<Object> data = new ArrayList<>();

    public List<Object> getdata() {
        String e_url = ""; //external API with above JSON data
        RestTemplate rt = new RestTemplate();
        Object[] test = rt.getForObject(e_url,Object[].class);
        data = Arrays.asList(test);
        return data;
    }

    public List<Object> getRetrievedData() {
        return data;
    }
}

Now, in your Controller2 you could get the retrieved data from the Service:

public class controller2 extends HttpServlet {

    private Service service; // Not really sure how to inject this here since for whatever 
        // reason you are using an `HttpServlet` instead of a regular Spring Boot Controller
    
    Public void doGet(HttpServletRequest request, HttpServletResponse response) throwsServletException {}
    Public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException {
        service.getRetrievedData();
    }
    Public static void pr(HttpServletRequest request, HttpServletResponse response, PrintWriter out) {
        //From here I want to display the JSON data to web interface which passes from controller 1
    }
}