How to move an email service into a thread?

Question

I am using Feign to connect two microservices. One of them composes the email and the other one sends it.

This is the Email Client:

@FeignClient("holiday-client")
public interface EmailClient {
    @RequestMapping(value = "/api/email/sendEmail", method = RequestMethod.POST)
    void sendEmail(@RequestBody Email email);
}

The service where the email is composed:

@Service
public class EmailService {
    @Autowired
    private EmailClient emailClient;

    public void sendEmailForNewCampaign() {
        String to, subject, body;

        to = "[email protected]";
        subject = "A new campaign has started";
        body = "This email has the purpose to inform you that a new campaign has been started. Please start your own performance reviews until it ends.";
        Email email = new Email(to, subject, body);
        emailClient.sendEmail(email);
    }
}

And the controller from the other microservice which actually sends the email:

@RestController
public class EmailController {

    @Autowired
    private EmailSender emailSender;

    @RequestMapping(value = "/api/email/sendEmail", method = RequestMethod.POST)
    public ResponseEntity sendEmail(@RequestBody Email email) {
        System.out.println(email); //printed 5 times
        emailSender.sendMail(email.getTo(), email.getSubject(), email.getBody());
        return new ResponseEntity(HttpStatus.ACCEPTED);
    }
}

It seems that this API is called 5 times until the email is processed and sent. It works cause I receive 5 emails, but I also got a SocketTimeOutException. The problem is that the client waits too long for the email service to send the mail and I don't want that. How can I move the method sendMail into a thread in order to solve this problem ?

Answer 1

Use @Async annotation on your service (or method).

@Service
@Async
public class EmailService 

Do not foget @EnableAsync