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    
018    package org.apache.commons.configuration;
019    
020    import java.util.HashMap;
021    
022    /**
023     * <p>A Configuration implementation that reads the platform specific
024     * environment variables using the map returned by {@link System#getenv()}.</p>
025     *
026     * <p>This configuration implementation is read-only. It allows read access to the
027     * defined OS environment variables, but their values cannot be changed. Any
028     * attempts to add or remove a property will throw an
029     * {@link UnsupportedOperationException}</p>
030     *
031     * <p>Usage of this class is easy: After an instance has been created the get
032     * methods provided by the {@code Configuration} interface can be used
033     * for querying environment variables, e.g.:</p>
034     *
035     * <pre>
036     * Configuration envConfig = new EnvironmentConfiguration();
037     * System.out.println("JAVA_HOME=" + envConfig.getString("JAVA_HOME");
038     * </pre>
039     *
040     * @author <a href="mailto:nicolas.deloof@gmail.com">Nicolas De Loof</a>
041     * @version $Id: EnvironmentConfiguration.java 1210171 2011-12-04 18:32:07Z oheger $
042     * @since 1.5
043     */
044    public class EnvironmentConfiguration extends MapConfiguration
045    {
046        /**
047         * Create a Configuration based on the environment variables.
048         *
049         * @see System#getenv()
050         */
051        public EnvironmentConfiguration()
052        {
053            super(new HashMap<String, Object>(System.getenv()));
054        }
055    
056        /**
057         * Adds a property to this configuration. Because this configuration is
058         * read-only, this operation is not allowed and will cause an exception.
059         *
060         * @param key the key of the property to be added
061         * @param value the property value
062         */
063        @Override
064        protected void addPropertyDirect(String key, Object value)
065        {
066            throw new UnsupportedOperationException("EnvironmentConfiguration is read-only!");
067        }
068    
069        /**
070         * Removes a property from this configuration. Because this configuration is
071         * read-only, this operation is not allowed and will cause an exception.
072         *
073         * @param key the key of the property to be removed
074         */
075        @Override
076        public void clearProperty(String key)
077        {
078            throw new UnsupportedOperationException("EnvironmentConfiguration is read-only!");
079        }
080    
081        /**
082         * Removes all properties from this configuration. Because this
083         * configuration is read-only, this operation is not allowed and will cause
084         * an exception.
085         */
086        @Override
087        public void clear()
088        {
089            throw new UnsupportedOperationException("EnvironmentConfiguration is read-only!");
090        }
091    }