/*

  * 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.lang.reflect.Method;

 import java.util.Collection;

 import java.util.HashMap;

 import java.util.Iterator;

 import java.util.Map;

 import org.apache.commons.lang.SystemUtils;

 import org.apache.tools.ant.taskdefs.Execute;

 /**

  * <p>

  * A Configuration implementation that reads the platform specific environment

  * variables. On pre java5 JRE it uses Ant Execute task to read the environment.

  * (in this case ant must be present in classpath). On java >= 5 JRE it uses

  * <code>java.lang.System#getenv()</code> and ant is not required.

  * </p>

  * <p>

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

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

  * </p>

  * <p>

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

  * methods provided by the <code>Configuration</code> interface can be used

  * for querying environment variables, e.g.:

  *

  * <pre>

  * Configuration envConfig = new EnvironmentConfiguration();

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

  * </pre>

  *

  * </p>

  *

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

  * @see org.apache.tools.ant.taskdefs.Execute#getProcEnvironment()

  * @since 1.5

  */

 public class EnvironmentConfiguration extends AbstractConfiguration

 {

     /** Constant for the name of the getenv() method. */

     private static final String METHOD_NAME = "getenv";

     /** Constant for the Java version 1.5. */

     private static final int VERSION_1_5 = 150;

     /** Stores the environment properties. */

     private Map environment;

     /**

      * Constructor.

      */

     public EnvironmentConfiguration()

     {

         if (SystemUtils.isJavaVersionAtLeast(VERSION_1_5))

         {

             extractProperties15();

         }

         else

         {

             extractProperties14();

         }

     }

     /**

      * 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

      */

     protected void addPropertyDirect(String key, Object value)

     {

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

     }

     /**

      * {@inheritDoc}

      *

      * @see org.apache.commons.configuration.AbstractConfiguration#containsKey(java.lang.String)

      */

     public boolean containsKey(String key)

     {

         return environment.containsKey(key);

     }

     /**

      * {@inheritDoc}

      *

      * @see org.apache.commons.configuration.AbstractConfiguration#getKeys()

      */

     public Iterator getKeys()

     {

         return environment.keySet().iterator();

     }

     /**

      * {@inheritDoc}

      *

      * @see org.apache.commons.configuration.AbstractConfiguration#getProperty(java.lang.String)

      */

     public Object getProperty(String key)

     {

         return environment.get(key);

     }

     /**

      * {@inheritDoc}

      *

      * @see org.apache.commons.configuration.AbstractConfiguration#isEmpty()

      */

     public boolean isEmpty()

     {

         return environment.isEmpty();

     }

     /**

      * 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

      */

     public void clearProperty(String key)

     {

         throw new UnsupportedOperationException("Configuration 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.

      */

     public void clear()

     {

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

     }

     /**

      * Extracts environment properties on a JRE < 1.5. This implementation

      * uses ant for this purpose.

      */

     void extractProperties14()

     {

         extractPropertiesFromCollection(Execute.getProcEnvironment());

     }

     /**

      * An internally used method for processing a collection with environment

      * entries. The collection must contain strings like

      * <code>property=value</code>. Such a collection is returned by ant.

      *

      * @param env the collection with the properties

      */

     void extractPropertiesFromCollection(Collection env)

     {

         environment = new HashMap();

         for (Iterator it = env.iterator(); it.hasNext();)

         {

             String entry = (String) it.next();

             int pos = entry.indexOf('=');

             if (pos == -1)

             {

                 getLogger().warn("Ignoring: " + entry);

             }

             else

             {

                 environment.put(entry.substring(0, pos), entry

                         .substring(pos + 1));

             }

         }

     }

     /**

      * Extracts environment properties on a JR >= 1.5. From this Java version

      * on, there is an official way of doing this. However because the code

      * should compile on lower Java versions, too, we have to invoke the method

      * using reflection.

      */

     void extractProperties15()

     {

         try

         {

             Method method = System.class.getMethod(METHOD_NAME, null);

             environment = (Map) method.invoke(null, null);

         }

         catch (Exception ex)

         {

             // this should normally not happen on a JRE >= 1.5

             throw new ConfigurationRuntimeException(

                     "Error when accessing environment properties", ex);

         }

     }

 }