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 * @since 1.5
041 */
042public class EnvironmentConfiguration extends MapConfiguration
043{
044    /**
045     * Create a Configuration based on the environment variables.
046     *
047     * @see System#getenv()
048     */
049    public EnvironmentConfiguration()
050    {
051        super(new HashMap<String, Object>(System.getenv()));
052    }
053
054    /**
055     * Adds a property to this configuration. Because this configuration is
056     * read-only, this operation is not allowed and will cause an exception.
057     *
058     * @param key the key of the property to be added
059     * @param value the property value
060     */
061    @Override
062    protected void addPropertyDirect(final String key, final Object value)
063    {
064        throw new UnsupportedOperationException("EnvironmentConfiguration is read-only!");
065    }
066
067    /**
068     * Removes a property from this configuration. Because this configuration is
069     * read-only, this operation is not allowed and will cause an exception.
070     *
071     * @param key the key of the property to be removed
072     */
073    @Override
074    protected void clearPropertyDirect(final String key)
075    {
076        throw new UnsupportedOperationException("EnvironmentConfiguration is read-only!");
077    }
078
079    /**
080     * Removes all properties from this configuration. Because this
081     * configuration is read-only, this operation is not allowed and will cause
082     * an exception.
083     */
084    @Override
085    protected void clearInternal()
086    {
087        throw new UnsupportedOperationException("EnvironmentConfiguration is read-only!");
088    }
089}