[TSS discussion] Spring 2.0 vs. the Anemic Domain Model

好, 又有一个机会兜售我的Nuts。这个热闹一定要掺和一下。

针对这个讨论，我写了一个wiki：
http://docs.codehaus.org/display/YAN/Simple+Rich+Domain+Injection

看看比起spring的rocket science如何。

Anemic is about domain logic
Posted by: Martin Fowler on December 13, 2005 in response to Message #193682 3 replies in this thread
Just to clarify (and I've added a para to the bliki entry too) my definition of an Anemic Domain Model is about the domain objects lacking domain logic. Persistence and/or Presentation logic are an entirely separate issue. I've seen (and helped build) good, rich domain models that have no connections to presentation or data sources and they worked well.

On the real issue of the article, there is value in injecting service objects into domain objects. Better examples would involve gateways to external systems that would be invoked due to the flow of the business logic.

ajoo，你的解决方案简单来说，就是不要new XXX，而是XXXFactory。不过blog作者在一开始就点明了很多情况下我们需要对new出来的对象进行DI。举例来说，以我们常用的Hibernate/Spring/Webwork的架构，实体类基本上不是在我们的应用程序中显式的通过new得到的，而是通过Hibernate，Webwork这样的框架在底层运行的时候隐式的得到的，你总不能去改Hibernate/Webwork的代码来适配你的XXXFactory吧？

例如从数据库得到对象  User user = (User) session.load(id);
Hibernate有一个隐式的new UserProxy()操作，返回给你一个UserProxy的对象，这时候你怎么织入XXXFactory？

再例如一个增加用户的页面提交，request paramters 是 user.name=robbin，Webwork使用ognl表达式调用，隐含了:
User user = new User(); user.setName("robbin");
这样的操作，你又如何织入UserFactory？

public class CustomerServiceImpl implements CustomerService {
  public CustomerServiceImpl(); {}  
  public void loadAndDoBusiness(Integer id); {
    Customer original = dao.load(id);;    
    Customer duplicate = factory.createCustomer();;
    duplicate.setId(original.getId(); + 1);;
    duplicate.setName(original.getName(););;
    
    original.setName("Michael Walls");;
    
    original.doBusiness();;
    duplicate.doBusiness();;
  }
  
  private final CustomerDao dao;
  private final CustomerFactory factory;
  public CustomerServiceImpl(CustomerDao dao, CustomerFactory factory);{
    this.dao = dao;
    this.factory = factory;
  }
}

你没看明白。我是说用factory来代替直接new。而从hibernate返回出来的对象是用proxy来注入。也就是说，原始的CustomerDao直接返回Hibernate生成的那个对象，然后有一个CustomerDao的dynamic proxy负责注射依赖。
那个<inject>就是干这个用的。

总的来说，从第三方库出来的对象都用dynamic proxy来注射，同时程序自己要生成对象就用factory。只要保证service使用的都是接口，容器就可以把依赖注射好。

你看这个CustomerService，它用了CustomerDao和CustomerFactory，CustomerDao封装了Hibernate，CustomerFactory代替"new"。从这两个接口返回的Customer对象都是已经把依赖注射好的。

public class CustomerServiceImpl implements CustomerService {
  public CustomerServiceImpl(); {}  
  public void loadAndDoBusiness(Integer id); {
    Customer original = dao.load(id);;    
    Customer duplicate = factory.createCustomer();;
    duplicate.setId(original.getId(); + 1);;
    duplicate.setName(original.getName(););;
    
    original.setName("Michael Walls");;
    
    original.doBusiness();;
    duplicate.doBusiness();;
  }
  
  private final CustomerDao dao;
  private final CustomerFactory factory;
  public CustomerServiceImpl(CustomerDao dao, CustomerFactory factory);{
    this.dao = dao;
    this.factory = factory;
  }
}

nothing ......
这么多言语，我实在看不出有什么新的东西，也没有什么可以鼓舞人心的东西。
还是套用一句话：老瓶装旧酒，外加一个新标签。
除了IOC ,IOC,Factory ,Factory还是IOC....Factory ....

如果仅仅是IOC,Factory,通过Factory获取Proxy对象，OK,please stop .
Spring已经够可爱的啦，够cool了，再来这么多围绕这个体系的框架，负面效果要高于正面效果。