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;
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    /** The configuration to which lookups are delegated. */
036    private final ImmutableConfiguration configuration;
037
038    /**
039     * Creates a new instance of {@code ConfigurationLookup} and sets the associated {@code ImmutableConfiguration}.
040     *
041     * @param config the configuration to use for lookups (must not be <b>null</b>)
042     * @throws IllegalArgumentException if the configuration is <b>null</b>
043     */
044    public ConfigurationLookup(final ImmutableConfiguration config) {
045        if (config == null) {
046            throw new IllegalArgumentException("Configuration must not be null!");
047        }
048        configuration = config;
049    }
050
051    /**
052     * Gets the {@code ImmutableConfiguration} used by this object.
053     *
054     * @return the associated {@code ImmutableConfiguration}
055     */
056    public ImmutableConfiguration getConfiguration() {
057        return configuration;
058    }
059
060    /**
061     * {@inheritDoc} This implementation calls {@code getProperty()} on the associated configuration. The return value is
062     * directly returned. Note that this may be a complex object, e.g. a collection or an array.
063     */
064    @Override
065    public Object lookup(final String variable) {
066        return getConfiguration().getProperty(variable);
067    }
068}