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 * this work for additional information regarding copyright ownership.
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 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.avalon.framework.service;

A ServiceSelector selects Objects based on a supplied policy. The contract is that all the Objects implement the same role. 
Author:
Avalon Development Team
See Also:
Serviceable
ServiceSelector
Version:
$Id: ServiceSelector.java 506231 2007-02-12 02:36:54Z crossley $/**
 * A <code>ServiceSelector</code> selects {@link Object}s based on a
 * supplied policy.  The contract is that all the {@link Object}s implement the
 * same role.
 *
 * @author <a href="mailto:dev@avalon.apache.org">Avalon Development Team</a>
 * @version $Id: ServiceSelector.java 506231 2007-02-12 02:36:54Z crossley $
 * @see org.apache.avalon.framework.service.Serviceable
 * @see org.apache.avalon.framework.service.ServiceSelector
 */
public interface ServiceSelector
{
    
Select the Object associated with the given policy. For instance, If the ServiceSelector has a Generator stored and referenced by a URL, the
following call could be used:
try
{
    Generator input;
    input = (Generator)selector.select( new URL("foo://demo/url") );
}
catch (...)
{
    ...
}

Params:
policy – A criteria against which a Object is selected.
Throws:
ServiceException – If the requested Object cannot be supplied
Returns:
an Object value/**
     * Select the {@link Object} associated with the given policy.
     * For instance, If the {@link ServiceSelector} has a
     * <code>Generator</code> stored and referenced by a URL, the
     * following call could be used:
     *
     * <pre>
     * try
     * {
     *     Generator input;
     *     input = (Generator)selector.select( new URL("foo://demo/url") );
     * }
     * catch (...)
     * {
     *     ...
     * }
     * </pre>
     *
     * @param policy A criteria against which a {@link Object} is selected.
     *
     * @return an {@link Object} value
     * @throws ServiceException If the requested {@link Object} cannot be supplied
     */
    Object select( Object policy )
        throws ServiceException;

    
Check to see if a Object exists relative to the supplied policy. 
Params:
policy – a Object containing the selection criteria
Returns:
True if the component is available, False if it not./**
     * Check to see if a {@link Object} exists relative to the supplied policy.
     *
     * @param policy a {@link Object} containing the selection criteria
     * @return True if the component is available, False if it not.
     */
    boolean isSelectable( Object policy );

    
Return the Object when you are finished with it. This allows the ServiceSelector to handle the End-Of-Life Lifecycle events associated with the Object. Please note, that no Exception should be thrown at this point. This is to allow easy use of the ServiceSelector system without having to trap Exceptions on a release. 
Params:
object – The Object we are releasing, may also be a null reference/**
     * Return the {@link Object} when you are finished with it.  This
     * allows the {@link ServiceSelector} to handle the End-Of-Life Lifecycle
     * events associated with the {@link Object}.  Please note, that no
     * Exception should be thrown at this point.  This is to allow easy use of the
     * ServiceSelector system without having to trap Exceptions on a release.
     *
     * @param object The {@link Object} we are releasing, may also be a 
     *               <code>null</code> reference
     */
    void release( Object object );
}