抽象工厂模式与2工厂方法

Question

In a spring hibernate java project with(controller - services - dao - entity layers), i am having abstract factory pattern (the abstract class has 2 abstract methods). In the implemented classes of abstract factory pattern i am having dao methods(to run the named queries). Now when the request comes to the service impl the dao from another Service class it gives null pointer excecption I have autowired the dao classes in the services impl `

AbstractFruitService - [addToBasket() and removeFromBasket()] 
|
|- SeasonalFruitsServicsImpl - SeasonalFruitsDAO
| 
|- BerryFruitsServiceImpl - BerryFruitsDAO

i cant add @Service("abstractFruitService") to both SeasonalFruitsServicsImpl and BerryFruitsServiceImpl it gives error - conflicts with existing, non-compatible bean definition of same name and class

Not sure if the spring static/instance factory method is useful in this case, i tries this also but didnt work

Is there any approach

Answer 1

What you are doing rather looks like a Service Locator pattern, Service Locator is an alternative to Dependency Injection. So there's no reason to implement one if you are already using IoC Spring Container.

Can declare your SeasonalFruitsServiceImpl and BerryFruitsServiceImpl as separate beans, and request their instances from the container either using their respective interfaces SeasonalFruitsDAO and BerryFruitsDAO , or by providing them with the separate names(if you need to replace the implementations then you just register another implementations in the container).

See Martin J. Fowler article

If the service locator was provided by some 3rd party then you should create an instance of Service Locator

<bean id="someServiceLocator" class="com.some3rdparty.ServiceLocator"/>
<bean id="seasonalFruitsDao" factory-bean="someServiceLocator" factory-method="createSeasonalFruitDao"/>
<bean id="berryFruitsDao" factory-bean="someServiceLocator" factory-method="createBerryFruitsDao"/>

or with java code configuration

@Configuration
public class someServiceLocatorConfiguration{
  @Bean
  public ServiceLocator locator(){
    return new com.some3rdparty.ServiceLocator();
  }
  @Bean()
  public SeasonalFruitsDao  seasonalFruitsDao(){
    return locator().createSeasonalFruitDao();
  }
  @Bean()
  public SeasonalFruitsDao  seasonalFruitsDao(){
    return locator().createSeasonalFruitDao();
  }
}

but of course you should never ever do it to instantiate objects developed by you.

Answer 2

使用注释@Transactional(propagation = Propagation.REQUIRES_NEW)非常适合我的代码，在服务方法上我添加了这个功能，它运行良好