Spring Autowire - 接口和实现需要DAO类吗？

Question

First off, I have done some reading and I am wondering what is the purpose of having a Interface and the implementation class for example the Data Access Objects (DAO)? I have read that it increases flexibility, but I was wondering if someone could provide a concrete example as to why we need an interface.

If we are autowiring, do we still need to use a Interface and Implementation that implement the interface? If so, why? Do we just need the impl?

Thank you in advance.

Answer 1

You don't strictly need an interface. But there are two reasons to prefer them:

• You can easily swap the implementation for testing purposes
• Proxy-ing beans for the purposes of aspect oriented programming or similar is easier (Java supports it out of the box)

Other reasons might be added, but these are the main 2 in my opinion. Still, don't feel forced to work like that. If the case you're working on does not warrant this flexibility, there's no need to complicate things.

And, by all means, never call your classes *Impl . If you can not come up with a proper name for the implementation, it means you shouldn't be having an interface to begin with.