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.configuration2.interpol;
18
19 /**
20 * <p>
21 * A specialized lookup implementation that allows access to environment variables.
22 * </p>
23 * <p>
24 * This implementation relies on {@link System#getenv()} to resolve environment variables. It can be used for
25 * referencing environment variables in configuration files in an easy way, for instance:
26 * </p>
27 *
28 * <pre>
29 * java.home = ${env:JAVA_HOME}
30 * </pre>
31 *
32 * <p>
33 * {@code EnvironmentLookup} is one of the standard lookups that is registered per default for each configuration.
34 * </p>
35 *
36 * @since 1.7
37 * @deprecated Use {@link DefaultLookups#ENVIRONMENT}.
38 */
39 @Deprecated
40 public class EnvironmentLookup implements Lookup {
41 /**
42 * Performs a lookup for the specified variable. This implementation directly delegates to a {@code System.getenv()}.
43 *
44 * @param key the key to lookup
45 * @return the value of this key or <b>null</b> if it cannot be resolved
46 */
47 @Override
48 public String lookup(final String key) {
49 return System.getenv(key);
50 }
51 }