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 }