001    // Copyright 2004, 2005 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    //     http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.tapestry.util;
016    
017    import org.apache.tapestry.engine.IPropertySource;
018    
019    /**
020     *  Obtain properties from JVM system properties.
021     * 
022     *
023     *  @author Howard Lewis Ship
024     *  @since 2.3
025     *
026     **/
027    
028    public class SystemPropertiesPropertySource implements IPropertySource
029    {
030        private static IPropertySource _shared;
031        
032        public static synchronized IPropertySource getInstance()
033        {
034            if (_shared == null)
035                _shared = new SystemPropertiesPropertySource();
036                
037            return _shared; 
038        }
039    
040        /**
041         *  Delegates to {@link System#getProperty(java.lang.String)}.
042         * 
043         **/
044        
045        public String getPropertyValue(String propertyName)
046        {
047            return System.getProperty(propertyName);
048        }
049    
050    }