In General: Writing custom implementations for Spring and Spring Security

Im using Spring Framework and Spring Security and I noticed that for Spring Security it is possible to write implementations for almost every class offered by Spring Security (lets say for Filters, Features (RememberMe) and so on). I like the possibility of writing custom implementations because it offers more flexibility and individuality.

Instead in Spring Framework itself I keep using the features offered (MVC, Annotations....) and not writing own impleme开发者_开发知识库ntations for anything. I haven't even got an idea where I could write my own implementation for. So I'd like to know if there are features from Spring Framework where own implementations can be written for? Or is it in general possible to write your own implementations for everything, just like in Spring Security?

Thanks for answering! :-)

The Spring Core Framwork has some variation and extension points. For example you can write your own Converters, ... To find more, have a look at the Interfaces provided by Spring, most of them exists, because someone should write a custom implementation for this interface.

But in general variation and extension becomes easier when you have a IOC Container. But the Spring Core itself can not use a IOC Container, because it is one. So because of this, it is not so easy to change every detail of the Spring Core. So at least it is easy to change the frameworks in some points where the Framework is designed to be changed. But it is hard to change the Framework in points where it is not designed to be changed.