Any simple boolean "discovery" methods should never throw an exception. It only complicates matters.
There comes two questions for the need for this approach:
1) If we are talking about NEEDED components that the calling Component must have in order to work, then we need to strengthen the contract between the parent and child Components. The Parent MUST know what its children NEED. Anything less is an incorrectly designed system.
Just an opinion from a user, having such a method would be good, because it will allow component developers to log potentially more meaningful messages regarding an incorrect component setup. In our situation here, the developers that are putting components together may not know as much about underlying dependencies. Of course, it would be nice for the system to handle that automagically, which is what I think you are getting at with your point above. Perhaps something like:
<role name="com.pace2020.appbox.framework.components.dataobject.DataFactory" shorthand="datafactory" default-class="com.pace2020.appbox.framework.components.dataobject.DataFactoryImpl">
<depends-on role="org.apache.avalon.excalibur.datasource.JdbcDataSource"/>
</role>
<role name="com.pace2020.appbox.framework.components.dataobject.DataManagerSelector" shorthand="data-objects" default-class="org.apache.avalon.excalibur.component.ExcaliburComponentSelector">
<hint shorthand="relating" class="com.pace2020.appbox.framework.components.dataobject.RelatingDataManagerImpl">
<depends-on role="com.pace2020.appbox.framework.components.dataobject.DataFactory"/>
</hint>
<hint shorthand="singleton" class="com.pace2020.appbox.framework.components.dataobject.SingletonDataManagerImpl">
<depends-on role="com.pace2020.appbox.framework.components.dataobject.DataFactory"/>
</hint>
</role>
The ComponentManager could then verify that all needed roles have been made available to it, perhaps before starting to initialize its components?
I would volunteer to implements something like this, but I embark upon a vaction next week and we are working towards an industry trade-show in September. I would be able to dedicate time after that, however.
-peter
-- peter royal -> [EMAIL PROTECTED] managing partners, inc. -> http://www.managingpartners.com
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