/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (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
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.avalon.framework.component;

import org.apache.avalon.framework.service.ServiceSelector;
import org.apache.avalon.framework.service.ServiceException;

This is a ServiceSelector implementation that can wrap around a legacy ComponentSelector object effectively adapting a ComponentSelector interface to a ServiceSelector interface. 
Author:
Avalon Development Team
Version:
$Id: WrapperComponentSelector.java 506231 2007-02-12 02:36:54Z crossley $
Since:
4.1.4/**
 * This is a {@link ServiceSelector} implementation that can wrap around a legacy
 * {@link ComponentSelector} object effectively adapting a {@link ComponentSelector}
 * interface to a {@link ServiceSelector} interface.
 *
 * @author <a href="mailto:dev@avalon.apache.org">Avalon Development Team</a>
 * @version $Id: WrapperComponentSelector.java 506231 2007-02-12 02:36:54Z crossley $
 * @since 4.1.4
 */
public class WrapperComponentSelector
    implements ComponentSelector
{
    
The Selector we are wrapping.
/**
     * The Selector we are wrapping.
     */
    private final ServiceSelector m_selector;

    
The role that this selector was aquired via.
/**
     * The role that this selector was aquired via.
     */
    private final String m_key;

    
This constructor is a constructor for a WrapperComponentSelector.
Params:
key – the key used to aquire this selector
selector – the selector to wrap/**
     * This constructor is a constructor for a WrapperComponentSelector.
     *
     * @param key the key used to aquire this selector
     * @param selector the selector to wrap
     */
    public WrapperComponentSelector( final String key,
                                     final ServiceSelector selector )
    {
        if( null == key )
        {
            throw new NullPointerException( "key" );
        }
        if( null == selector )
        {
            throw new NullPointerException( "selector" );
        }

        m_key = key + "/";
        m_selector = selector;
    }

    
Select a Component based on a policy.
Params:
policy – the policy
Throws:
ComponentException – if unable to select service
Returns:
the Component/**
     * Select a Component based on a policy.
     *
     * @param policy the policy
     * @return the Component
     * @throws ComponentException if unable to select service
     */
    public Component select( final Object policy )
        throws ComponentException
    {
        try
        {
            final Object object = m_selector.select( policy );
            if( object instanceof Component )
            {
                return (Component)object;
            }
        }
        catch( final ServiceException se )
        {
            throw new ComponentException( m_key + policy, se.getMessage(), se );
        }

        final String message = "Role does not implement the Component " 
           + "interface and thus can not be accessed via ComponentSelector";
        throw new ComponentException( m_key + policy, message );
    }

    
Check to see if a Component 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 Component} 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.
     */
    public boolean hasComponent( final Object policy )
    {
        return m_selector.isSelectable( 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./**
     * 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.
     */
    public void release( final Component object )
    {
        m_selector.release( object );
    }

    
The WrapperComponentManager wraps ServiceSelectors in WrapperServiceSelectors when they are looked up. This method makes it possible to release the original component selector. 
Returns:
The ServiceSelector being wrapped./**
     * The {@link WrapperComponentManager} wraps ServiceSelectors in
     *  WrapperServiceSelectors when they are looked up.  This method
     *  makes it possible to release the original component selector.
     *
     * @return The {@link ServiceSelector} being wrapped.
     */
    ServiceSelector getWrappedSelector()
    {
        return m_selector;
    }
}