001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 package org.apache.commons.configuration.interpol; 018 019 import org.apache.commons.configuration.EnvironmentConfiguration; 020 import org.apache.commons.lang.text.StrLookup; 021 022 /** 023 * <p> 024 * A specialized lookup implementation that allows access to environment 025 * variables. 026 * </p> 027 * <p> 028 * This implementation relies on {@link EnvironmentConfiguration} to resolve 029 * environment variables. It can be used for referencing environment variables 030 * in configuration files in an easy way, for instance: 031 * 032 * <pre> 033 * java.home = ${env:JAVA_HOME} 034 * </pre> 035 * 036 * </p> 037 * <p> 038 * {@code EnvironmentLookup} is one of the standard lookups that is 039 * registered per default for each configuration. 040 * </p> 041 * 042 * @author <a 043 * href="http://commons.apache.org/configuration/team-list.html">Commons 044 * Configuration team</a> 045 * @since 1.7 046 * @version $Id: EnvironmentLookup.java 1210620 2011-12-05 20:57:31Z oheger $ 047 */ 048 public class EnvironmentLookup extends StrLookup 049 { 050 /** Stores the underlying {@code EnvironmentConfiguration}. */ 051 private final EnvironmentConfiguration environmentConfig = new EnvironmentConfiguration(); 052 053 /** 054 * Performs a lookup for the specified variable. This implementation 055 * directly delegates to a {@code EnvironmentConfiguration}. 056 * 057 * @param key the key to lookup 058 * @return the value of this key or <b>null</b> if it cannot be resolved 059 */ 060 @Override 061 public String lookup(String key) 062 { 063 return environmentConfig.getString(key); 064 } 065 }