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.configuration2;
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 * @since 1.5
042 */
043public class EnvironmentConfiguration extends MapConfiguration
044{
045    /**
046     * Create a Configuration based on the environment variables.
047     *
048     * @see System#getenv()
049     */
050    public EnvironmentConfiguration()
051    {
052        super(new HashMap<String, Object>(System.getenv()));
053    }
054
055    /**
056     * Adds a property to this configuration. Because this configuration is
057     * read-only, this operation is not allowed and will cause an exception.
058     *
059     * @param key the key of the property to be added
060     * @param value the property value
061     */
062    @Override
063    protected void addPropertyDirect(final String key, final Object value)
064    {
065        throw new UnsupportedOperationException("EnvironmentConfiguration is read-only!");
066    }
067
068    /**
069     * Removes a property from this configuration. Because this configuration is
070     * read-only, this operation is not allowed and will cause an exception.
071     *
072     * @param key the key of the property to be removed
073     */
074    @Override
075    protected void clearPropertyDirect(final String key)
076    {
077        throw new UnsupportedOperationException("EnvironmentConfiguration is read-only!");
078    }
079
080    /**
081     * Removes all properties from this configuration. Because this
082     * configuration is read-only, this operation is not allowed and will cause
083     * an exception.
084     */
085    @Override
086    protected void clearInternal()
087    {
088        throw new UnsupportedOperationException("EnvironmentConfiguration is read-only!");
089    }
090}