framework/src/net/sf/tapestry/util/DelegatingPropertySource.java

/*
 *  ====================================================================
 *  The Apache Software License, Version 1.1
 *
 *  Copyright (c) 2002 The Apache Software Foundation.  All rights
 *  reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions
 *  are met:
 *
 *  1. Redistributions of source code must retain the above copyright
 *  notice, this list of conditions and the following disclaimer.
 *
 *  2. Redistributions in binary form must reproduce the above copyright
 *  notice, this list of conditions and the following disclaimer in
 *  the documentation and/or other materials provided with the
 *  distribution.
 *
 *  3. The end-user documentation included with the redistribution,
 *  if any, must include the following acknowledgment:
 *  "This product includes software developed by the
 *  Apache Software Foundation (http://www.apache.org/)."
 *  Alternately, this acknowledgment may appear in the software itself,
 *  if and wherever such third-party acknowledgments normally appear.
 *
 *  4. The names "Apache" and "Apache Software Foundation" and
 *  "Apache Tapestry" must not be used to endorse or promote products
 *  derived from this software without prior written permission. For
 *  written permission, please contact apache@apache.org.
 *
 *  5. Products derived from this software may not be called "Apache",
 *  "Apache Tapestry", nor may "Apache" appear in their name, without
 *  prior written permission of the Apache Software Foundation.
 *
 *  THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 *  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 *  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 *  DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 *  ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 *  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 *  USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 *  ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 *  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 *  OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 *  SUCH DAMAGE.
 *  ====================================================================
 *
 *  This software consists of voluntary contributions made by many
 *  individuals on behalf of the Apache Software Foundation.  For more
 *  information on the Apache Software Foundation, please see
 *  <http://www.apache.org/>.
 */
package net.sf.tapestry.util;

import java.util.ArrayList;
import java.util.List;

import net.sf.tapestry.IPropertySource;

/**
 *  An implementation of {@link net.sf.tapestry.IPropertySource}
 *  that delegates to a list of other implementations.  This makes
 *  it possible to create a search path for property values.
 *
 *  @author Howard Lewis Ship
 *  @version $Id$
 *  @since 2.3
 *
 **/

public class DelegatingPropertySource implements IPropertySource
{
    private List _sources = new ArrayList();
    
    public DelegatingPropertySource()
    {
    }
    
    public DelegatingPropertySource(IPropertySource delegate)
    {
        addSource(delegate);
    }
    
    /**
     *  Adds another source to the list of delegate property sources.
     *  This is typically only done during initialization
     *  of this DelegatingPropertySource.
     * 
     **/
    
    public void addSource(IPropertySource source)
    {
        _sources.add(source);
    }
    
    /**
     *  Re-invokes the method on each delegate property source, 
     *  in order, return the first non-null value found.
     * 
     **/
    
    public String getPropertyValue(String propertyName)
    {
        String result = null;
        int count = _sources.size();
        
        for (int i = 0; i < count; i++)
        {
            IPropertySource source = (IPropertySource)_sources.get(i);
            
            result = source.getPropertyValue(propertyName);
            
            if (result != null)
                break;
        }
        
        return result;        
    }

}