Re: [Springframework-developer] Dependency checking

[<rod...@in...>]

All,

As I can see it the only arguable advantage that 
PicoContainer has over Spring is that it can satisfy all 
dependencies before allowing an object to be invoked, so that 
an object can never be used when incompletely configured. I 
don't like their constructor way of doing this, and I think 
that it often makes sense to have optional properties, with 
sensible default. So I've never been worried by this in 
Spring.

However, it's pretty easy to add optional dependency 
checking. I've successfully prototyped the following, which 
required very minor changes:
- add a new DTD attribute for the "bean" element called 
dependencyCheck
- if this is set to true, XmlBeanFactory checks that all 
properties on that bean have been set. If not it throws an 
UnsatisfiedDependencyException. We can't do the PicoContainer-
style automatic wiring up as we can support multiple objects 
of any type. They can only accomplish this because they 
support only a single object of each type, which doesn't 
satisfy the kind of real-world requirements I've used Spring 
in.

At present my prototype checks only Object properties 
(presumably other beans in the factory). It might be good to 
have three values for dependencyCheck: "no" 
(default), "object" (collaborators) and "all" (primitives and 
collaborators).

As this is backward compatible and easy to do I'm inclined to 
add it, if only for marketing value. There may be real value 
in that it means that an init method wouldn't need to check 
that a certain property was non-null.

What do you think? Is this worthwhile?

Regards,
Rod