이메일 발송 JavaMail

# application.properties
spring.mail.host=smtp.gmail.com
spring.mail.port=587
spring.mail.username=${MAIL_USERNAME}
spring.mail.password=${MAIL_PASSWORD}
spring.mail.properties.mail.smtp.auth=true
spring.mail.properties.mail.smtp.starttls.enable=true

// EmailService.java
@Service
@RequiredArgsConstructor
public class EmailService {
    private final JavaMailSender mailSender;

    // 기본 텍스트 메일
    public void sendSimple(String to, String subject, String text) {
        SimpleMailMessage msg = new SimpleMailMessage();
        msg.setTo(to);
        msg.setSubject(subject);
        msg.setText(text);
        mailSender.send(msg);
    }

    // HTML 메일
    public void sendHtml(String to, String subject, String html)
            throws MessagingException {
        MimeMessage msg = mailSender.createMimeMessage();
        MimeMessageHelper helper = new MimeMessageHelper(msg, true, "UTF-8");
        helper.setTo(to);
        helper.setSubject(subject);
        helper.setText(html, true); // true = HTML
        mailSender.send(msg);
    }

    // 인증 코드 발송
    @Async
    public void sendVerificationCode(String to, String code) {
        String html = "<h2>인증 코드: <strong>" + code + "</strong></h2>";
        try { sendHtml(to, "[OPEN HYPER STEP] 이메일 인증", html); }
        catch (MessagingException e) { throw new RuntimeException(e); }
    }
}