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
018package org.apache.commons.configuration;
019
020import 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 */
044public 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}