org.apache.avalon.framework.component
Interface ComponentSelector

All Superinterfaces:

Component

All Known Implementing Classes:

DefaultComponentSelector, WrapperComponentSelector

public interface ComponentSelector

extends Component

A ComponentSelector selects Components based on a hint. The contract is that all the Components implement the same role.

A role is better understood by the analogy of a play. There are many different roles in a script. Any actor or actress can play any given part and you get the same results (phrases said, movements made, etc.). The exact nuances of the performance is different.

Below is a list of things that might be considered the same role:

• XMLInputAdapter and PropertyInputAdapter
• FileGenerator and SQLGenerator

The ComponentSelector does not specify the methodology of getting the Component, merely the interface used to get it. Therefore the ComponentSelector can be implemented with a factory pattern, an object pool, or a simple Hashtable.

Deprecated: Use ServiceSelector instead.

Version:

CVS $Revision: 1.19 $ $Date: 2003/02/11 15:58:38 $

Author:

Avalon Development Team

See Also:

Component, Composable, ComponentManager

Method Summary

boolean	hasComponent(Object hint) Check to see if a Component exists for a hint.
void	release(Component component) Return the Component when you are finished with it.
Component	select(Object hint) Select the Component associated with the given hint.

Method Detail

select

public Component select(Object hint)
                 throws ComponentException

Select the Component associated with the given hint. For instance, If the ComponentSelector has a Generator stored and referenced by a URL, I would use the following call:

 try
 {
     Generator input;
     input = (Generator)selector.select( new URL("foo://demo/url") );
 }
 catch (...)
 {
     ...
 }
 

Parameters:

hint - A hint to retrieve the correct Component.

Returns:

the desired component

Throws:

ComponentException - If the given role is not associated with a Component, or a Component instance cannot be created.

hasComponent

public boolean hasComponent(Object hint)

Check to see if a Component exists for a hint.

Parameters:

hint - a string identifying the role to check.

Returns:

True if the component exists, False if it does not.

release

public void release(Component component)

Return the Component when you are finished with it. This allows the ComponentSelector to handle the End-Of-Life Lifecycle events associated with the Component. Please note, that no Exceptions should be thrown at this point. This is to allow easy use of the ComponentSelector system without having to trap Exceptions on a release.

Parameters:

component - The Component we are releasing.