[Springframework-developer] Enhancing NameSpaceHandler initialization

[Yan P. <ypu...@li...>]

Hello

I am new to this list but have been working with spring for several  
years now. I work at a company called LinkedIn and we use spring  
extensively (I can count over 1000 spring files in our source code as  
of today)... Very early on when spring was not as easily extensible  
(prior to 2.0) we actually extended it by inheriting a lot of classes  
(we basically wanted the ability to have our own tags in xml files).  
Then when namespace handling came along we created our own namespace  
and were able to get rid of all the custom extensions we had done.

I am pretty familiar with the spring source code since I had to  
extend it in several ways in the past.

I created the following Jira enhacement [http:// 
jira.springframework.org/browse/SPR-4729] and posted a patch that  
implements it.

Like I mention in my comment in the jira ticket, I think that the  
concept of namespace is an amazing way to tailor the behavior of  
spring to our needs without having to hook ourselves deep in the  
framework. The  two examples that I currently have on top of my head  
are:

* like spring offers a set of custom property editors, we have a set  
of custom property editors for types that our company use (like  
MemorySize, Timespan... which allow us to write "30g" or "3h20m" in  
our spring files)
* we also have our own set of lifecycle interfaces. Spring offers  
DisposableBean, our company has its own version. We want that those  
beans that we create with our own interface get disposed properly  
(One of the beauty of spring is that you should be able to use it  
without having your code depend on it)

I know that I can do both of these things by 'registering' custom  
property editors and BeanPostProcessor. I obviously don't want to  
have to do that in every single spring file...
I can obviously write my own tag <linkedIn:init/> that can do the  
trick, but it is one more thing to remember to add to the spring file  
and if you don't then suddenly the lifecycle does not work.

What I think would be awesome is if I could do this by simply  
registering the namespace
<beans xmlns="http://www.springframework.org/schema/beans"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xmlns:lin="http://www.linkedin.com/lispring"
   xsi:schemaLocation="http://www.springframework.org/schema/beans  
http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
                            http://www.linkedin.com/lispring http:// 
www.linkedin.com/lispring/lispring.xsd">
</beans>

The problem is that today the init() method on NamespaceHandler does  
not take any argument. What I suggest as an enhancement is to simply  
take an initializing context which at least gives access to the bean  
registry, so that we can 'tweak' it before even any bean is registered.

The patch I posted is doing just that but most likely not in the best  
way, it was just a try. There are many many ways to do it, especially  
if we want to remain backward compatible. (For example we could  
create a NameSpaceHandlerInitContext class instead of passing the  
class I am currently providing...)

So I would just like to know:

a) what do you guys think about this change ?
b) if you think it is ok to change it, I am entirely ok to implement  
it the way it needs to be and post a patch to be integrated in the  
source code. But I just need to know what is the 'correct' way to  
implement it.

As a side note, we just started to use osgi and by simply creating a  
bundle with our custom spring namespace, it works magically with  
spring dm...

Thanks in adavance
Yan Pujante
Distinguished Software Engineer, LinkedIn Corporation
http://www.linkedin.com/in/yan