7

鉴于：

  1. Spring MVC - 休眠。
  2. 控制器 -> 服务 -> DAO
  3. 现在我有一个从数据库中检索某些东西的方法，并且每次它这样做时，都必须执行另一种方法，例如“processList”（就像根据某些屏幕参数更改列表中的某些值一样）。

问题：

  1. 我把这个“processList”放在哪一层？（控制器、服务或 DAO？为什么）

我现在真的需要一些 j2ee 澄清，我知道 MVC 在不同语言中是相同的，但我只需要确定 :) 如果我在 .net 中执行此操作，我无疑会将其投入使用。

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1 回答 1

19

This really depends on what processList is doing exactly. There is no golden rule. Some rules I try to follow are:

  1. Never make calls between main objects on the same layer.
    • ManagementServiceImpl should never call NotificationServiceImpl.
  2. Don't make circular dependencies between objects.
    • This is very similar to the one above.
  3. If you find yourself repeating some logic across multiple main object, try to restructure the code and extract it in specialized logical classes (this will improve unit-testing as well).
    • E.g. UserUpdateHandler or NotificationDispatcher (these are still owned by the service layer -> noone else is allowed to call them)...
  4. Put the code where it logically belongs.
    • Don't get distracted by the fact, that some class needs to do something. It might not be the right place for the code.
  5. Never write fully generalised code before you need to.
    • This has its term as premature generalisation, which is a bad practice similar to premature optimisation. Saving few lines of code now can lead to pulling your hair out in the future.
  6. Always write code which is able to become generalised.
    • This is not a contradiction with the previous. This says - always write with generalisation in mind, however don't bother with writing if it is not needed. Think ahead, but not necessarily act ahead.
  7. Leave business logic to service layer, data persistence logic to data layer and user interaction logic to presentation layer.
    • Don't try to parse user input in service layer. This does not belong there similarly as counting final price in e-shop application does not belong to presentation layer.

Some examples for processList:

  • Example I - fetching additional relations via Hibernate#initialize
    • This is something which is really in between the service and DAO layer. On older projects we had specialized FetchHandler class (owned by service layer). In newer projects we leave this completely to DAOs.
  • Example II - go through list and add business validation messages to the result
    • service layer, no doubt
  • Example III - go through the list and prepare UI messages based on the validation errors
    • presentation layer

Side note:

  • MVC is a different thing from three-layered architecture.
  • M model spans across all three layers. Presentation layer includes both V views and C controllers.
于 2013-06-16T08:24:37.047 回答