How to call rest API in the loop

Question

I want to call the third party API multiple times using the RestTemplate(for each customer id I have to call REST API) currently I have written like below and its working fine but it's taking time because there are many customers I'd and calling API for each customer id, is there any way I can make this parallel.

 public List<Organization> getCustomeOrganizationInfo(){
   String url="https://url.net/core/v1/customers"
   List<Organization> organizationList = new ArrayList<>();

    for(Customer customer:CustomerList){

      String restUrlWithUserId=url+"/customer.getCustomerId"

        CustomerInfo customerInfo = restTemplate.exchange(
                restUrlWithUserId,
                HttpMethod.GET,
                request,
                String.class
        );
        
    Organization organization =new Organization();
    organization.setCustomerId(customer.getCustomerId())
    organization.setorganizationId(customerInfo.getCustomeOrganizationId())
    organization.setorganizationname(customerInfo.getCustomeOrganizationName())
        
   organizationList.add(organization)       
}

}

Answer 1

Is there any way I can make this parallel

For concurrency and clean code, you should separate your restTemplate call to another class(service), for example, ThirdPartyCustomerService.java. This class will be held responsible for calling outside.

@Service
public class ThirdPartyCustomerService {
   private final RestTemplate restTemplate;
   private final String url = '...';
   ...
   public CustomerInfo getCustomerInfo() {
       return this.restTemplate...
   }
}

Then you can inject this class into your service class. Now if you want to run it concurrency. You could try @Async and Future here. Just need a little bit of change on the new service and remember to call Future.get() on your main service.

@Async
public Future<CustomerInfo> getCustomerInfo() {
   return new AsyncResult<CustomerInfo>(this.restTemplate...);
}

Or you can use WebClient, an alternative for RestTemplate and AsyncRestTemplate.