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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *     http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.configuration;
18  
19  import java.lang.reflect.Method;
20  import java.util.Collection;
21  import java.util.HashMap;
22  import java.util.Iterator;
23  import java.util.Map;
24  
25  import org.apache.commons.lang.SystemUtils;
26  import org.apache.tools.ant.taskdefs.Execute;
27  
28  /***
29   * <p>
30   * A Configuration implementation that reads the platform specific environment
31   * variables. On pre java5 JRE it uses Ant Execute task to read the environment.
32   * (in this case ant must be present in classpath). On java >= 5 JRE it uses
33   * <code>java.lang.System#getenv()</code> and ant is not required.
34   * </p>
35   * <p>
36   * This configuration implementation is read-only. It allows read access to the
37   * defined OS environment variables, but their values cannot be changed.
38   * </p>
39   * <p>
40   * Usage of this class is easy: After an instance has been created the get
41   * methods provided by the <code>Configuration</code> interface can be used
42   * for querying environment variables, e.g.:
43   *
44   * <pre>
45   * Configuration envConfig = new EnvironmentConfiguration();
46   * System.out.println("JAVA_HOME=" + envConfig.getString("JAVA_HOME");
47   * </pre>
48   *
49   * </p>
50   *
51   * @author <a href="mailto:nicolas.deloof@gmail.com">Nicolas De Loof</a>
52   * @see org.apache.tools.ant.taskdefs.Execute#getProcEnvironment()
53   * @since 1.5
54   */
55  public class EnvironmentConfiguration extends AbstractConfiguration
56  {
57      /*** Constant for the name of the getenv() method. */
58      private static final String METHOD_NAME = "getenv";
59  
60      /*** Constant for the Java version 1.5. */
61      private static final int VERSION_1_5 = 150;
62  
63      /*** Stores the environment properties. */
64      private Map environment;
65  
66      /***
67       * Constructor.
68       */
69      public EnvironmentConfiguration()
70      {
71          if (SystemUtils.isJavaVersionAtLeast(VERSION_1_5))
72          {
73              extractProperties15();
74          }
75          else
76          {
77              extractProperties14();
78          }
79      }
80  
81      /***
82       * Adds a property to this configuration. Because this configuration is
83       * read-only, this operation is not allowed and will cause an exception.
84       *
85       * @param key the key of the property to be added
86       * @param value the property value
87       */
88      protected void addPropertyDirect(String key, Object value)
89      {
90          throw new UnsupportedOperationException("Configuration is read-only!");
91      }
92  
93      /***
94       * {@inheritDoc}
95       *
96       * @see org.apache.commons.configuration.AbstractConfiguration#containsKey(java.lang.String)
97       */
98      public boolean containsKey(String key)
99      {
100         return environment.containsKey(key);
101     }
102 
103     /***
104      * {@inheritDoc}
105      *
106      * @see org.apache.commons.configuration.AbstractConfiguration#getKeys()
107      */
108     public Iterator getKeys()
109     {
110         return environment.keySet().iterator();
111     }
112 
113     /***
114      * {@inheritDoc}
115      *
116      * @see org.apache.commons.configuration.AbstractConfiguration#getProperty(java.lang.String)
117      */
118     public Object getProperty(String key)
119     {
120         return environment.get(key);
121     }
122 
123     /***
124      * {@inheritDoc}
125      *
126      * @see org.apache.commons.configuration.AbstractConfiguration#isEmpty()
127      */
128     public boolean isEmpty()
129     {
130         return environment.isEmpty();
131     }
132 
133     /***
134      * Removes a property from this configuration. Because this configuration is
135      * read-only, this operation is not allowed and will cause an exception.
136      *
137      * @param key the key of the property to be removed
138      */
139     public void clearProperty(String key)
140     {
141         throw new UnsupportedOperationException("Configuration is read-only!");
142     }
143 
144     /***
145      * Removes all properties from this configuration. Because this
146      * configuration is read-only, this operation is not allowed and will cause
147      * an exception.
148      */
149     public void clear()
150     {
151         throw new UnsupportedOperationException("Configuration is read-only!");
152     }
153 
154     /***
155      * Extracts environment properties on a JRE &lt; 1.5. This implementation
156      * uses ant for this purpose.
157      */
158     void extractProperties14()
159     {
160         extractPropertiesFromCollection(Execute.getProcEnvironment());
161     }
162 
163     /***
164      * An internally used method for processing a collection with environment
165      * entries. The collection must contain strings like
166      * <code>property=value</code>. Such a collection is returned by ant.
167      *
168      * @param env the collection with the properties
169      */
170     void extractPropertiesFromCollection(Collection env)
171     {
172         environment = new HashMap();
173         for (Iterator it = env.iterator(); it.hasNext();)
174         {
175             String entry = (String) it.next();
176             int pos = entry.indexOf('=');
177             if (pos == -1)
178             {
179                 getLogger().warn("Ignoring: " + entry);
180             }
181             else
182             {
183                 environment.put(entry.substring(0, pos), entry
184                         .substring(pos + 1));
185             }
186         }
187     }
188 
189     /***
190      * Extracts environment properties on a JR &gt;= 1.5. From this Java version
191      * on, there is an official way of doing this. However because the code
192      * should compile on lower Java versions, too, we have to invoke the method
193      * using reflection.
194      */
195     void extractProperties15()
196     {
197         try
198         {
199             Method method = System.class.getMethod(METHOD_NAME, null);
200             environment = (Map) method.invoke(null, null);
201         }
202         catch (Exception ex)
203         {
204             // this should normally not happen on a JRE >= 1.5
205             throw new ConfigurationRuntimeException(
206                     "Error when accessing environment properties", ex);
207         }
208     }
209 }