How to run the method in background while i am adding the data in database in springboot?

Question

I am trying to fetch the data and store it in database.

Created a Get mapping for invoking the data from url and storing it in database using service class .

@GetMapping("/")
public String root(Model model) throws IOException {
    model.addAttribute("test1","Hello user");
    service.populate();
    return "mainTemplate";
}

my populate method in service class add data to database.

public void populate() throws IOException{
        URL url = new URL("https://raw.githubusercontent.com/CSSEGISandData/COVID-19/master/csse_covid_19_data/csse_covid_19_daily_reports/01-01-2021.csv"); 
        HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
        int res= connection.getResponseCode();
        CSVReader reader=null;
        if(res==200) {
        log.info("Connected to github");
        
        try {
          BufferedReader readurl = new BufferedReader(new InputStreamReader(connection.getInputStream()),8192);
            reader=new CSVReader(readurl);
            
            
            String[] line;
            int i=0;
            while((line=reader.readNext())!=null) {
                
                if(i==0) {
                    i++;
                    continue;
                }
                DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
                Corona corona = new Corona();
                corona.setLastupDate(LocalDateTime.parse(line[4],formatter));
                corona.setConfirmed(Long.valueOf(line[7]));
                corona.setRecovered(Long.valueOf(line[9]));
                corona.setActive(Long.valueOf(line[10]));
                corona.setCombinedKey(line[11]);
                log.info(corona.toString());
                repo.save(corona);
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (CsvValidationException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } 
        finally {
            if(reader!=null) {
                
                try {
                    reader.close();
                    
                } catch (IOException e2) {
                    // TODO: handle exception
                    e2.printStackTrace();
                }
            }
            
        }
        
        }
        else {
            log.info("URL is wrong");
        }
        
    }

Everything is working fine when i hit the resource url ,but i have to wait for some time to show my webpage , until all data does not get stored in database.

I want to show "Data is being added" in mainTemplate.html as soon as i hit the url. So that my populate method runs in background and i don't have to wait for completion of method to show my mainTemplate .

I tired to add @Async method annotation but that does not seem to be worked .