/*

  * Licensed to the Apache Software Foundation (ASF) under one or more

  * contributor license agreements.  See the NOTICE file distributed with

  * this work for additional information regarding copyright ownership.

  * The ASF licenses this file to You under the Apache License, Version 2.0

  * (the "License"); you may not use this file except in compliance with

  * the License.  You may obtain a copy of the License at

  *

  *     http://www.apache.org/licenses/LICENSE-2.0

  *

  * Unless required by applicable law or agreed to in writing, software

  * distributed under the License is distributed on an "AS IS" BASIS,

  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

  * See the License for the specific language governing permissions and

  * limitations under the License.

  */

 package org.apache.commons.configuration;

 import java.util.HashMap;

 /**

  * <p>A Configuration implementation that reads the platform specific

  * environment variables using the map returned by {@link System#getenv()}.</p>

  *

  * <p>This configuration implementation is read-only. It allows read access to the

  * defined OS environment variables, but their values cannot be changed. Any

  * attempts to add or remove a property will throw an

  * {@link UnsupportedOperationException}</p>

  *

  * <p>Usage of this class is easy: After an instance has been created the get

  * methods provided by the {@code Configuration} interface can be used

  * for querying environment variables, e.g.:</p>

  *

  * <pre>

  * Configuration envConfig = new EnvironmentConfiguration();

  * System.out.println("JAVA_HOME=" + envConfig.getString("JAVA_HOME");

  * </pre>

  *

  * @author <a href="mailto:nicolas.deloof@gmail.com">Nicolas De Loof</a>

  * @version $Id: EnvironmentConfiguration.java 1210171 2011-12-04 18:32:07Z oheger $

  * @since 1.5

  */

 public class EnvironmentConfiguration extends MapConfiguration

 {

     /**

      * Create a Configuration based on the environment variables.

      *

      * @see System#getenv()

      */

     public EnvironmentConfiguration()

     {

         super(new HashMap<String, Object>(System.getenv()));

     }

     /**

      * Adds a property to this configuration. Because this configuration is

      * read-only, this operation is not allowed and will cause an exception.

      *

      * @param key the key of the property to be added

      * @param value the property value

      */

     @Override

     protected void addPropertyDirect(String key, Object value)

     {

         throw new UnsupportedOperationException("EnvironmentConfiguration is read-only!");

     }

     /**

      * Removes a property from this configuration. Because this configuration is

      * read-only, this operation is not allowed and will cause an exception.

      *

      * @param key the key of the property to be removed

      */

     @Override

     public void clearProperty(String key)

     {

         throw new UnsupportedOperationException("EnvironmentConfiguration is read-only!");

     }

     /**

      * Removes all properties from this configuration. Because this

      * configuration is read-only, this operation is not allowed and will cause

      * an exception.

      */

     @Override

     public void clear()

     {

         throw new UnsupportedOperationException("EnvironmentConfiguration is read-only!");

     }

 }