[xwiki-devs] [Proposal] Add support for JSR330 Provider - xwiki-devs@xwiki.org

10 Nov 2011

Hi devs,

I've started investigating this. The documentation for Provider can be found here:
http://code.google.com/p/atinject/source/browse/trunk/src/javax/inject/Prov…

Here's we would define a provider:

@Component
public class MyProvider implements Provider<RoleToProvide>
{
    @Inject <-- just to show that a provider is a component and be injected other
components
    private SomeRole role;

    @Override
    public RoleToProvide get()
    {
        … logic here to return a RoleToProvide instance…
    }
}

And here's how you'd use it:

@Component
public class MyComponent implements MyRole
{
…
    @Inject
    private Provider<RoleToProvide> provider;
…
    public void someMethod()
    {
        RoleToProvide instance = this.provider.get();
…

Rationale:
=========

* UC1: Useful to break cyclic dependencies in a cleaner way than having the
ComponentManager injected, especially since the Provider can be reused since it's
shared
* UC2: Useful to clean up code so that the logic to decide which implementation to return
can be externalized in a Provider implementation. For example imagine you have a config
property in xwiki.properties and based on it you wish to return a component with one hint
or another. You could use a Provider for this.
* Allows us to be JSR330 compliant (not a very strong point but still an argument ;))

Default Provider
=============

When you ask to get injected a Provider if no Provider is defined for the Role you wish,
you'll get injected a generic provider which simply does a lookup using the Component
Manager. This allows to simply implement UC1.

WDYT?

Thanks
-Vincent