View Javadoc

1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *     http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.configuration.interpol;
18  
19  import org.apache.commons.configuration.EnvironmentConfiguration;
20  import org.apache.commons.lang.text.StrLookup;
21  
22  /**
23   * <p>
24   * A specialized lookup implementation that allows access to environment
25   * variables.
26   * </p>
27   * <p>
28   * This implementation relies on {@link EnvironmentConfiguration} to resolve
29   * environment variables. It can be used for referencing environment variables
30   * in configuration files in an easy way, for instance:
31   *
32   * <pre>
33   * java.home = ${env:JAVA_HOME}
34   * </pre>
35   *
36   * </p>
37   * <p>
38   * {@code EnvironmentLookup} is one of the standard lookups that is
39   * registered per default for each configuration.
40   * </p>
41   *
42   * @author <a
43   *         href="http://commons.apache.org/configuration/team-list.html">Commons
44   *         Configuration team</a>
45   * @since 1.7
46   * @version $Id: EnvironmentLookup.java 1210620 2011-12-05 20:57:31Z oheger $
47   */
48  public class EnvironmentLookup extends StrLookup
49  {
50      /** Stores the underlying {@code EnvironmentConfiguration}. */
51      private final EnvironmentConfiguration environmentConfig = new EnvironmentConfiguration();
52  
53      /**
54       * Performs a lookup for the specified variable. This implementation
55       * directly delegates to a {@code EnvironmentConfiguration}.
56       *
57       * @param key the key to lookup
58       * @return the value of this key or <b>null</b> if it cannot be resolved
59       */
60      @Override
61      public String lookup(String key)
62      {
63          return environmentConfig.getString(key);
64      }
65  }