@RequestMapping(value = { "" }, method = RequestMethod.GET)
public ResponseEntity<?> greet(@PathVariable Optional<Integer> productId) {

    List<Products> products = productService.findAllCategories();
    int count = products.size(); // also want to include this as count like below response
    return new ResponseEntity<List<Products>>(products, HttpStatus.OK);
}

{
  "count": 23,
  "products":[
     {..},
     {..}
   ]
}

class ProductsDTO {

  private int count;
  private List<Products> products;

  /* create setters and getters for the fields */

}

@RequestMapping(value = { "" }, method = RequestMethod.GET)
public ResponseEntity<?> greet(@PathVariable Optional<Integer> productId) {

List<Products> products = productService.findAllCategories();
int count = products.size();
ProductsDTO productsDTO = new ProductsDTO();
productsDTO.setCount(count);
productsDTO.setProducts(products);
return new ResponseEntity<ProductsDTO>(productsDTO, HttpStatus.OK);
}

<dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-core</artifactId>
      <version>2.8.5</version>
  </dependency>
  <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
      <version>2.8.5</version>
  </dependency>

@RequestMapping(value = "/locations", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<?> getAll() {
    List<Location> locations  = locationService.getLocations();
    List<Country> countries = countryService.getCountries();

    Map<String, Object> result = new HashMap<String,Object>();
    result.put("count",locations.size());
    result.put("locations",locations);
    result.put("countries",countries);
    // Add any additional props that you want to add
    return new ResponseEntity<Map<String,Object>>(result, HttpStatus.OK);
}

curl -H "Accept: application/json" -H "Content-type: application/json" -X GET http://localhost:8080/api/locations

@RequestMapping(value = { "/{productId}", "" }, method = RequestMethod.GET)
public ResponseEntity<?> greet(@PathVariable Optional<Integer> productId) {
    List<Products> products = productService.findAllCategories();

    HashMap<String, Object> hmap = new HashMap<String, Object>();
    hmap.put("count", products.size());
    hmap.put("products", products);
    // Now I can put as many properties as I want

    return new ResponseEntity<HashMap<String, Object>>(hmap, HttpStatus.OK);
}

@RestController
@RequestMapping("/api")
public class RestApiController {
    @Autowired
    RepoCity repoCity;

    @Autowired
    RepoCountry repoCountry;

    @Autowired
    RepoLanguage repoLanguage;

    @GetMapping("/allTotal")
    public Map actionAllTotal() {
        Map map = new HashMap();
        map.put("repoCity",repoCity.count());
        map.put("repoCountry",repoCountry.count());
        map.put("repoLanguage",repoLanguage.count());
        Map result = new HashMap();;
        result.put("result",map);
        return result;
    }

    @GetMapping("/country-detail/{id}")
    public Map actionCountryDetail(@PathVariable("id") String id) {
        Map result = new HashMap();
        result.put("result",repoCountry.findOne(id));
        return result;
    }
}