解决Springboot 自动注入报空指针问题

最近做发送邮件的功能，因为邮件的种类有多种，所以使用了多态，工厂模式。建立了一个抽象接口，以及实现类，根据传入不同的邮件类型进行调用不同类中的方法。
但是遇到了问题，在调用实现类时，发现实现类中自动注入的service不生效，全部为空。
代码如下

     IShMessageEmailService shMessageEmailService;
        if (messageType.equals("etaMessage")) {
            shMessageEmailService = new ShMessageEmailEtaService();
            text = shMessageEmailService.getMessageText(dynamicEntity, sailingSchedule, messageType);
        } else if (messageType.equals("etdMessage")) {
            shMessageEmailService = new ShMessageEmailEtdService();
            text = shMessageEmailService.getMessageText(dynamicEntity, sailingSchedule, messageType);
        }

@Service
public class ShMessageEmailEtaService extends BusinessService implements IShMessageEmailService {

    @Autowired
    private ShManifestCargoService shManifestCargoService;
    @Autowired
    private ShipPortService shipPortService;
  @Override
    public String getMessageText(ShDynamic dynamic, SailingSchedule sailingSchedule, String messageType) {
        ShManifestCargo shManifestCargo = shManifestCargoService.findImpCargoAndBlNo(sailingSchedule.getId());
        String loadPortCode = "";

检查后发现，又来是spring的service管理问题，如果用了spring管理bean 就不能自己new出来，然后修正了代码

@Autowired
    private ShMessageEmailEtaService shMessageEmailEtaService;
    @Autowired
    private ShMessageEmailEtdService shMessageEmailEtdService;

 IShMessageEmailService shMessageEmailService;
        if (messageType.equals("etaMessage")) {
            shMessageEmailService = shMessageEmailEtaService;
            text = shMessageEmailService.getMessageText(dynamicEntity, sailingSchedule, messageType);
        } else if (messageType.equals("etdMessage")) {
            shMessageEmailService = shMessageEmailEtdService;
            text = shMessageEmailService.getMessageText(dynamicEntity, sailingSchedule, messageType);
        }

这样就ok了。