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1   package org.codehaus.plexus.interpolation;
2   
3   /*
4    * Copyright 2001-2008 Codehaus Foundation.
5    *
6    * Licensed under the Apache License, Version 2.0 (the "License");
7    * you may not use this file except in compliance with the License.
8    * You may obtain a copy of the License at
9    *
10   *      http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  
19  import java.util.Properties;
20  
21  /**
22   * {@link ValueSource} implementation that wraps a {@link Properties} instance,
23   * and does a simple lookup of the entire expression string as the parameter for
24   * {@link Properties#getProperty(String)}, returning the result as the resolved
25   * value.
26   *
27   * @author jdcasey
28   * @version $Id$
29   */
30  public class PropertiesBasedValueSource
31      extends AbstractValueSource
32  {
33  
34      private final Properties properties;
35  
36      /**
37       * Wrap the specified {@link Properties} object for use as a value source.
38       * Nulls are allowed.
39       *
40       * @param properties The properties instance to wrap.
41       */
42      public PropertiesBasedValueSource( Properties properties )
43      {
44          super( false );
45          this.properties = properties;
46      }
47  
48      /**
49       * @return the result of {@link Properties#getProperty(String)}, using the
50       * entire expression as the key to lookup. If the wrapped properties instance
51       * is null, simply return null.
52       */
53      public Object getValue( String expression )
54      {
55          return properties == null ? null : properties.getProperty( expression );
56      }
57  
58  }