Usecase:
tapestry-spring-security offers integration between Tapestry 5 an Spring
Security [1]. It's implemented as a Tapestry IoC/Core module.
This module uses a PasswordEncoder shipped by Spring Security (they ship
also a couple of standard implementations of PasswordEncoder).
For the module to function correctly an implementation class of
PasswordEncoder (the service in charge) is needed. Now, there are two
ways to configure the module:
1.) gracefully: The module declares a standard service for
PasswordEncoder and assumes the main module will define an
AliasContribution to override with whatever specific instance is needed.
2.) tough: The module doesn't declare a standard service for
PasswordEncoder. It rather assumes that the user of the module will do
so. If the user of the module doesn't provide an implementation a
RuntimeException is thrown and the container won't start up.
Obviously there are arguments for both directions. In
tapestry-spring-security we wanted to follow line 1.) This leads us to
the FAQ.
[FAQ] How to configure a service that likely will be overriden by an
AliasContribution?
i. Supplier: The only thing the supplier of a module has to do is to
bind the interface (PasswordEncoder) to the default class
(PlaintextPasswordEncoder) - or provide a build method if he needs to
set it up.
public static void bind(final ServiceBinder binder) {
binder.bind( PasswordEncoder.class,
PlaintextPasswordEncoder.class ).withMarker(
SpringSecurityServices.class);
}
ii. User: Now if you want to use a supplied module and you want to
override a service defined there the only thing you have to do is to
contribute to the Alias service.
public static void contributeAlias(
Configuration<AliasContribution<PasswordEncoder>> configuration ) {
configuration.add( AliasContribution.create(
PasswordEncoder.class,
new ShaPasswordEncoder() ) );
}
--
Crowd,
Is this correct? Do I miss something?
Regards,
Michael
[1] http://www.localhost.nu/java/tapestry5-acegi/
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