    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}