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 */
017package org.apache.commons.configuration2.interpol;
018
019import org.apache.commons.lang3.text.StrLookup;
020
021/**
022 * <p>
023 * A specialized implementation of the {@code Lookup} interface that allows
024 * access to system properties.
025 * </p>
026 * <p>
027 * This implementation relies on {@code StrLookup.systemPropertiesLookup()} from
028 * the Commons Lang project to resolve system properties. It can be used for
029 * referencing system properties in configuration files in an easy way, for
030 * instance:
031 * </p>
032 *
033 * <pre>
034 * current.user = ${sys:user.name}
035 * </pre>
036 *
037 * <p>
038 * {@code SystemPropertiesLookup} is one of the standard lookups that is
039 * registered per default for each configuration.
040 * </p>
041 *
042 * @version $Id: SystemPropertiesLookup.java 1679786 2015-05-16 17:47:09Z oheger $
043 * @since 2.0
044 */
045public class SystemPropertiesLookup implements Lookup
046{
047    /** The underlying StrLookup object. */
048    private final StrLookup<String> sysLookup = StrLookup
049            .systemPropertiesLookup();
050
051    @Override
052    public Object lookup(String variable)
053    {
054        return sysLookup.lookup(variable);
055    }
056}