4、通知渠道适配器模式：适配器设计模式、各渠道（邮件、短信、推送）适配器实现

在用户通知体系中，不同的通知渠道（邮件、短信、App推送）拥有各自独立的API和协议。为了统一调用方式、降低系统耦合度，我们引入适配器设计模式。适配器模式如同一个“万能插头转换器”，将不同渠道的差异接口转换为统一的INotificationChannel接口，让上层业务代码无需关心底层实现细节。

📌 适配目标：将 JavaMail / SendGrid 等邮件SDK统一为 INotificationChannel

// 目标接口
public interface INotificationChannel {
    boolean send(NotificationRequest request);
    ChannelType getType();
}

// 邮件适配器
public class EmailAdapter implements INotificationChannel {
    private final JavaMailSender mailSender;  // 适配者

    public EmailAdapter(JavaMailSender mailSender) {
        this.mailSender = mailSender;
    }

    @Override
    public boolean send(NotificationRequest request) {
        try {
            MimeMessage message = mailSender.createMimeMessage();
            MimeMessageHelper helper = new MimeMessageHelper(message, true);
            helper.setTo(request.getRecipient());
            helper.setSubject(request.getTitle());
            helper.setText(request.getContent(), true);  // 支持HTML
            mailSender.send(message);
            return true;
        } catch (Exception e) {
            log.error("邮件发送失败: {}", e.getMessage());
            return false;
        }
    }

    @Override
    public ChannelType getType() {
        return ChannelType.EMAIL;
    }
}

📌 适配目标：将阿里云短信 / Twilio 等短信SDK统一为 INotificationChannel

// 短信适配器
public class SmsAdapter implements INotificationChannel {
    private final AliyunSmsClient smsClient;  // 适配者

    public SmsAdapter(AliyunSmsClient smsClient) {
        this.smsClient = smsClient;
    }

    @Override
    public boolean send(NotificationRequest request) {
        try {
            SendSmsRequest smsReq = new SendSmsRequest()
                .setPhoneNumbers(request.getRecipient())
                .setSignName("通知系统")
                .setTemplateCode("SMS_123456")
                .setTemplateParam("{\"code\":\"" + request.getContent() + "\"}");
            SendSmsResponse response = smsClient.sendSms(smsReq);
            return "OK".equals(response.getCode());
        } catch (Exception e) {
            log.error("短信发送失败: {}", e.getMessage());
            return false;
        }
    }

    @Override
    public ChannelType getType() {
        return ChannelType.SMS;
    }
}

📌 适配目标：将极光推送 / Firebase Cloud Messaging 统一为 INotificationChannel

// 推送适配器
public class PushAdapter implements INotificationChannel {
    private final JPushClient jpushClient;  // 适配者

    public PushAdapter(JPushClient jpushClient) {
        this.jpushClient = jpushClient;
    }

    @Override
    public boolean send(NotificationRequest request) {
        try {
            PushPayload payload = PushPayload.newBuilder()
                .setPlatform(Platform.all())
                .setAudience(Audience.alias(request.getRecipient()))
                .setNotification(Notification.newBuilder()
                    .setAlert(request.getTitle())
                    .addAndroidNotification(request.getTitle(), request.getContent(), null)
                    .addIosNotification(request.getTitle(), request.getContent())
                    .build())
                .build();
            PushResult result = jpushClient.sendPush(payload);
            return result.getStatusCode() == 200;
        } catch (Exception e) {
            log.error("推送发送失败: {}", e.getMessage());
            return false;
        }
    }

    @Override
    public ChannelType getType() {
        return ChannelType.PUSH;
    }
}

// 适配器工厂 - 统一管理所有渠道适配器
@Component
public class NotificationAdapterFactory {
    private final Map<ChannelType, INotificationChannel> adapterMap = new HashMap<>();

    public NotificationAdapterFactory(
            EmailAdapter emailAdapter,
            SmsAdapter smsAdapter,
            PushAdapter pushAdapter) {
        adapterMap.put(ChannelType.EMAIL, emailAdapter);
        adapterMap.put(ChannelType.SMS, smsAdapter);
        adapterMap.put(ChannelType.PUSH, pushAdapter);
    }

    public INotificationChannel getAdapter(ChannelType type) {
        INotificationChannel adapter = adapterMap.get(type);
        if (adapter == null) {
            throw new IllegalArgumentException("不支持的渠道类型: " + type);
        }
        return adapter;
    }
}

// 业务层统一调用
@Service
public class NotificationService {
    @Autowired
    private NotificationAdapterFactory adapterFactory;

    public boolean sendNotification(NotificationRequest request) {
        INotificationChannel adapter = adapterFactory.getAdapter(request.getChannelType());
        return adapter.send(request);
    }
}

💡 设计要点总结

• 每个渠道适配器只负责协议转换，不包含业务逻辑
• 适配器内部可加入重试、熔断、日志等横切关注点
• 新增渠道（如模板消息）只需新增一个Adapter实现类
• 适配器模式让通知系统具备良好的扩展性和可维护性