Reference articles
https://segmentfault.com/a/1190000015766938
https://blog.csdn.net/qq_34545192/article/details/80484780

1. Add @ EnableAsync annotation to the startup class of springboot

@SpringBootApplication
@EnableAsync
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}

2. Add ThreadConfig configuration class

@Configuration
@EnableAsync
public class ThreadConfig implements AsyncConfigurer {

    @Override
    public Executor getAsyncExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(10);
        executor.setMaxPoolSize(15);
        executor.setQueueCapacity(25);
        executor.initialize();
        return executor;
    }

    @Override
    public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
        return null;
    }
}

3. Let's write the business implementation of the multithreaded part.

@Component
public class EmailTool {
    @Autowired
    JavaMailSender javaMailSender;

    @Value("${spring.mail.username}")
    private String sendFrom; //Read the parameters in the configuration file

    @Async
    public void sendEmailAsync(EmailEntity emailEntity, CountDownLatch latch) {
        sendEmail(emailEntity);
        latch.countDown();
    }

    public void sendEmail(EmailEntity emailEntity) {
        MimeMessage message = javaMailSender.createMimeMessage();
        MimeMessageHelper helper;
        try {
            helper = new MimeMessageHelper(message, true);//Here you can customize the mailing name
            helper.setFrom(sendFrom);
            helper.setTo(emailEntity.getSendTo());
            helper.setSubject(emailEntity.getSubject());
            helper.setText(emailEntity.getMessage(),
                    true);
        } catch (MessagingException e) {
            e.printStackTrace();
        }
        javaMailSender.send(message);
    }
}

@ Invalidity of Async

Asynchronous methods and invocation methods must be written in different classes. If they are written in one class, they are ineffective.