Asynchronous REST client

Question

How to write asynchronous REST client?

My controller (not sure if it's enough for being async):

@RequestMapping(method = RequestMethod.GET, value = "/get/all")
@ResponseBody
public Callable < CustomersListDTO > getAllCustomers() {
    return new Callable < CustomersListDTO > () {

        @Override
        public CustomersListDTO call() throws Exception {
            Thread.sleep(2000);
            return customerService.getAllCustomers();
        }

    };
}

My synchronous REST client method:

public Response get_all_customers() {
    ResponseEntity < CustomersListDTO > response;
    try {
        response = restTemplate.getForEntity(
            getMethodURI(ServiceExplanation.GET_ALL_CUSTOMERS),
            CustomersListDTO.class
        );
        message = "Customers obtained successfully!";
    } catch (HttpServerErrorException ex) {
        message = "ERROR: " + ex.getMessage() + " - " + ex.getResponseBodyAsString();
    } catch (HttpClientErrorException ex) {
        message = "ERROR: " + ex.getMessage() + " - " + ex.getResponseBodyAsString();
    } catch (RestClientException ex) {
        message = checkIfServerOrInternetDown();
    }

    return formResponse(message, response);
}

How do I make it asynchronous? How can the CLIENT continue doing other tasks while SERVER is obtaining data and later return found data?

Solution

If you are looking for REST asynchronous client implementation, you can take a look at Jersey's asynchronous client API. It can be easily integrated with Spring.