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 *     https://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;
018
019import org.apache.commons.configuration2.interpol.Lookup;
020
021/**
022 * <p>
023 * A specialized implementation of the {@code Lookup} interface which uses a {@code Configuration} object to resolve
024 * variables.
025 * </p>
026 * <p>
027 * This class is passed an {@link ImmutableConfiguration} object at construction time. In its implementation of the
028 * {@code lookup()} method it simply queries this configuration for the passed in variable name. So the keys passed to
029 * {@code lookup()} are mapped directly to configuration properties.
030 * </p>
031 *
032 * @since 2.0
033 */
034public class ConfigurationLookup implements Lookup {
035
036    /** The configuration to which lookups are delegated. */
037    private final ImmutableConfiguration configuration;
038
039    /**
040     * Creates a new instance of {@code ConfigurationLookup} and sets the associated {@code ImmutableConfiguration}.
041     *
042     * @param config the configuration to use for lookups (must not be <strong>null</strong>)
043     * @throws IllegalArgumentException if the configuration is <strong>null</strong>
044     */
045    public ConfigurationLookup(final ImmutableConfiguration config) {
046        if (config == null) {
047            throw new IllegalArgumentException("Configuration must not be null!");
048        }
049        configuration = config;
050    }
051
052    /**
053     * Gets the {@code ImmutableConfiguration} used by this object.
054     *
055     * @return the associated {@code ImmutableConfiguration}
056     */
057    public ImmutableConfiguration getConfiguration() {
058        return configuration;
059    }
060
061    /**
062     * {@inheritDoc} This implementation calls {@code getProperty()} on the associated configuration. The return value is
063     * directly returned. Note that this may be a complex object, for example a collection or an array.
064     */
065    @Override
066    public Object lookup(final String variable) {
067        return getConfiguration().getProperty(variable);
068    }
069}