Coverage Report - org.apache.commons.configuration.SubnodeConfiguration
 
Classes in this File Line Coverage Branch Coverage Complexity
SubnodeConfiguration
100%
52/52
100%
8/8
2,2
 
 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.util.ArrayList;
 20  
 import java.util.Collections;
 21  
 import java.util.Iterator;
 22  
 import java.util.List;
 23  
 
 24  
 import org.apache.commons.configuration.tree.ConfigurationNode;
 25  
 
 26  
 /**
 27  
  * <p>
 28  
  * A specialized hierarchical configuration class that wraps a single node of
 29  
  * its parent configuration.
 30  
  * </p>
 31  
  * <p>
 32  
  * Configurations of this type are initialized with a parent configuration and a
 33  
  * configuration node of this configuration. This node becomes the root node of
 34  
  * the subnode configuration. All property accessor methods are evaluated
 35  
  * relative to this root node. A good use case for a
 36  
  * <code>SubnodeConfiguration</code> is when multiple properties from a
 37  
  * specific sub tree of the whole configuration need to be accessed. Then a
 38  
  * <code>SubnodeConfiguration</code> can be created with the parent node of
 39  
  * the affected sub tree as root node. This allows for simpler property keys and
 40  
  * is also more efficient.
 41  
  * </p>
 42  
  * <p>
 43  
  * A subnode configuration and its parent configuration operate on the same
 44  
  * hierarchy of configuration nodes. So if modifications are performed at the
 45  
  * subnode configuration, these changes are immideately visible in the parent
 46  
  * configuration. Analogously will updates of the parent configuration affect
 47  
  * the subnode configuration if the sub tree spanned by the subnode
 48  
  * configuration's root node is involved.
 49  
  * </p>
 50  
  * <p>
 51  
  * There are however changes at the parent configuration, which cause the
 52  
  * subnode configuration to become detached. An example for such a change is a
 53  
  * reload operation of a file-based configuration, which replaces all nodes of
 54  
  * the parent configuration. The subnode configuration per default still
 55  
  * references the old nodes. Another example are list structures: a subnode
 56  
  * configuration can be created to point on the <em>i</em>th element of the
 57  
  * list. Now list elements can be added or removed, so that the list elements'
 58  
  * indices change. In such a scenario the subnode configuration would always
 59  
  * point to the same list element, regardless of its current index.
 60  
  * </p>
 61  
  * <p>
 62  
  * To solve these problems and make a subnode configuration aware of
 63  
  * such structural changes of its parent, it is possible to associate a
 64  
  * subnode configuration with a configuration key. This can be done by calling
 65  
  * the <code>setSubnodeKey()</code> method. If here a key is set, the subnode
 66  
  * configuration will evaluate it on each access, thus ensuring that it is
 67  
  * always in sync with its parent. In this mode the subnode configuration really
 68  
  * behaves like a live-view on its parent. The price for this is a decreased
 69  
  * performance because now an additional evaluation has to be performed on each
 70  
  * property access. So this mode should only be used if necessary; if for
 71  
  * instance a subnode configuration is only used for a temporary convenient
 72  
  * access to a complex configuration, there is no need to make it aware for
 73  
  * structural changes of its parent. If a subnode configuration is created
 74  
  * using the <code>{@link HierarchicalConfiguration#configurationAt(String, boolean)
 75  
  * configurationAt()}</code> method of <code>HierarchicalConfiguration</code>
 76  
  * (which should be the preferred way), with an additional boolean parameter it
 77  
  * can be specified whether the resulting subnode configuration should be
 78  
  * aware of structural changes or not. Then the configuration key will be
 79  
  * automatically set.
 80  
  * </p>
 81  
  * <p>
 82  
  * <em>Note:</em> At the moment support for creating a subnode configuration
 83  
  * that is aware of structural changes of its parent from another subnode
 84  
  * configuration (a "sub subnode configuration") is limited. This only works if
 85  
  * <ol><li>the subnode configuration that serves as the parent for the new
 86  
  * subnode configuration is itself associated with a configuration key and</li>
 87  
  * <li>the key passed in to create the new subnode configuration is not too
 88  
  * complex (if configuration keys are used that contain indices, a corresponding
 89  
  * key that is valid from the parent configuration's point of view cannot be
 90  
  * constructed).</li></ol>
 91  
  * </p>
 92  
  * <p>
 93  
  * When a subnode configuration is created, it inherits the settings of its
 94  
  * parent configuration, e.g. some flags like the
 95  
  * <code>throwExceptionOnMissing</code> flag or the settings for handling list
 96  
  * delimiters) or the expression engine. If these settings are changed later in
 97  
  * either the subnode or the parent configuration, the changes are not visible
 98  
  * for each other. So you could create a subnode configuration, change its
 99  
  * expression engine without affecting the parent configuration.
 100  
  * </p>
 101  
  * <p>
 102  
  * From its purpose this class is quite similar to
 103  
  * <code>{@link SubsetConfiguration}</code>. The difference is that a subset
 104  
  * configuration of a hierarchical configuration may combine multiple
 105  
  * configuration nodes from different sub trees of the configuration, while all
 106  
  * nodes in a subnode configuration belong to the same sub tree. If an
 107  
  * application can live with this limitation, it is recommended to use this
 108  
  * class instead of <code>SubsetConfiguration</code> because creating a subset
 109  
  * configuration is more expensive than creating a subnode configuration.
 110  
  * </p>
 111  
  *
 112  
  * @since 1.3
 113  
  * @author Oliver Heger
 114  
  * @version $Id: SubnodeConfiguration.java 531254 2007-04-22 18:54:57Z oheger $
 115  
  */
 116  
 public class SubnodeConfiguration extends HierarchicalConfiguration
 117  
 {
 118  
     /**
 119  
      * The serial version UID.
 120  
      */
 121  
     private static final long serialVersionUID = 3105734147019386480L;
 122  
 
 123  
     /** Stores the parent configuration. */
 124  
     private HierarchicalConfiguration parent;
 125  
 
 126  
     /** Stores the key that was used to construct this configuration.*/
 127  
     private String subnodeKey;
 128  
 
 129  
     /**
 130  
      * Creates a new instance of <code>SubnodeConfiguration</code> and
 131  
      * initializes it with the parent configuration and the new root node.
 132  
      *
 133  
      * @param parent the parent configuration
 134  
      * @param root the root node of this subnode configuration
 135  
      */
 136  
     public SubnodeConfiguration(HierarchicalConfiguration parent, ConfigurationNode root)
 137  240
     {
 138  240
         if (parent == null)
 139  
         {
 140  1
             throw new IllegalArgumentException(
 141  
                     "Parent configuration must not be null!");
 142  
         }
 143  239
         if (root == null)
 144  
         {
 145  1
             throw new IllegalArgumentException("Root node must not be null!");
 146  
         }
 147  
 
 148  238
         setRootNode(root);
 149  238
         this.parent = parent;
 150  238
         initFromParent(parent);
 151  238
     }
 152  
 
 153  
     /**
 154  
      * Returns the parent configuration of this subnode configuration.
 155  
      *
 156  
      * @return the parent configuration
 157  
      */
 158  
     public HierarchicalConfiguration getParent()
 159  
     {
 160  574
         return parent;
 161  
     }
 162  
 
 163  
     /**
 164  
      * Returns the key that was used to construct this configuration. If here a
 165  
      * non-<b>null</b> value is returned, the subnode configuration will
 166  
      * always check its parent for structural changes and reconstruct itself if
 167  
      * necessary.
 168  
      *
 169  
      * @return the key for selecting this configuration's root node
 170  
      * @since 1.5
 171  
      */
 172  
     public String getSubnodeKey()
 173  
     {
 174  611
         return subnodeKey;
 175  
     }
 176  
 
 177  
     /**
 178  
      * Sets the key to the root node of this subnode configuration. If here a
 179  
      * key is set, the subnode configuration will behave like a live-view on its
 180  
      * parent for this key. See the class comment for more details.
 181  
      *
 182  
      * @param subnodeKey the key used to construct this configuration
 183  
      * @since 1.5
 184  
      */
 185  
     public void setSubnodeKey(String subnodeKey)
 186  
     {
 187  8
         this.subnodeKey = subnodeKey;
 188  8
     }
 189  
 
 190  
     /**
 191  
      * Returns the root node for this configuration. If a subnode key is set,
 192  
      * this implementation re-evaluates this key to find out if this subnode
 193  
      * configuration needs to be reconstructed. This ensures that the subnode
 194  
      * configuration is always synchronized with its parent configuration.
 195  
      *
 196  
      * @return the root node of this configuration
 197  
      * @since 1.5
 198  
      * @see #setSubnodeKey(String)
 199  
      */
 200  
     public ConfigurationNode getRootNode()
 201  
     {
 202  593
         if (getSubnodeKey() != null)
 203  
         {
 204  
             try
 205  
             {
 206  10
                 List nodes = getParent().fetchNodeList(getSubnodeKey());
 207  9
                 if (nodes.size() != 1)
 208  
                 {
 209  
                     // key is invalid, so detach this subnode configuration
 210  1
                     setSubnodeKey(null);
 211  1
                 }
 212  
                 else
 213  
                 {
 214  8
                     ConfigurationNode currentRoot = (ConfigurationNode) nodes
 215  
                             .get(0);
 216  8
                     if (currentRoot != super.getRootNode())
 217  
                     {
 218  
                         // the root node was changed due to a change of the
 219  
                         // parent
 220  4
                         setRootNode(currentRoot);
 221  
                     }
 222  8
                     return currentRoot;
 223  
                 }
 224  
             }
 225  1
             catch (Exception ex)
 226  
             {
 227  
                 // Evaluation of the key caused an exception. Probably the
 228  
                 // expression engine has changed on the parent. Detach this
 229  
                 // configuration, there is not much we can do about this.
 230  1
                 setSubnodeKey(null);
 231  1
             }
 232  
         }
 233  
 
 234  585
         return super.getRootNode(); // use stored root node
 235  
     }
 236  
 
 237  
     /**
 238  
      * Returns a hierarchical configuration object for the given sub node.
 239  
      * This implementation will ensure that the returned
 240  
      * <code>SubnodeConfiguration</code> object will have the same parent than
 241  
      * this object.
 242  
      *
 243  
      * @param node the sub node, for which the configuration is to be created
 244  
      * @return a hierarchical configuration for this sub node
 245  
      */
 246  
     protected SubnodeConfiguration createSubnodeConfiguration(ConfigurationNode node)
 247  
     {
 248  84
         SubnodeConfiguration result = new SubnodeConfiguration(getParent(), node);
 249  84
         getParent().registerSubnodeConfiguration(result);
 250  84
         return result;
 251  
     }
 252  
 
 253  
     /**
 254  
      * Returns a hierarchical configuration object for the given sub node that
 255  
      * is aware of structural changes of its parent. Works like the method with
 256  
      * the same name, but also sets the subnode key for the new subnode
 257  
      * configuration, so it can check whether the parent has been changed. This
 258  
      * only works if this subnode configuration has itself a valid subnode key.
 259  
      * So if a subnode configuration that should be aware of structural changes
 260  
      * is created from an already existing subnode configuration, this subnode
 261  
      * configuration must also be aware of such changes.
 262  
      *
 263  
      * @param node the sub node, for which the configuration is to be created
 264  
      * @param subnodeKey the construction key
 265  
      * @return a hierarchical configuration for this sub node
 266  
      * @since 1.5
 267  
      */
 268  
     protected SubnodeConfiguration createSubnodeConfiguration(
 269  
             ConfigurationNode node, String subnodeKey)
 270  
     {
 271  2
         SubnodeConfiguration result = createSubnodeConfiguration(node);
 272  
 
 273  2
         if (getSubnodeKey() != null)
 274  
         {
 275  
             // construct the correct subnode key
 276  
             // determine path to root node
 277  1
             List lstPathToRoot = new ArrayList();
 278  1
             ConfigurationNode top = super.getRootNode();
 279  1
             ConfigurationNode nd = node;
 280  2
             while (nd != top)
 281  
             {
 282  1
                 lstPathToRoot.add(nd);
 283  1
                 nd = nd.getParentNode();
 284  1
             }
 285  
 
 286  
             // construct the keys for the nodes on this path
 287  1
             Collections.reverse(lstPathToRoot);
 288  1
             String key = getSubnodeKey();
 289  1
             for (Iterator it = lstPathToRoot.iterator(); it.hasNext();)
 290  
             {
 291  1
                 key = getParent().getExpressionEngine().nodeKey(
 292  
                         (ConfigurationNode) it.next(), key);
 293  1
             }
 294  1
             result.setSubnodeKey(key);
 295  
         }
 296  
 
 297  2
         return result;
 298  
     }
 299  
 
 300  
     /**
 301  
      * Creates a new node. This task is delegated to the parent.
 302  
      *
 303  
      * @param name the node's name
 304  
      * @return the new node
 305  
      */
 306  
     protected Node createNode(String name)
 307  
     {
 308  5
         return getParent().createNode(name);
 309  
     }
 310  
 
 311  
     /**
 312  
      * Initializes this subnode configuration from the given parent
 313  
      * configuration. This method is called by the constructor. It will copy
 314  
      * many settings from the parent.
 315  
      *
 316  
      * @param parentConfig the parent configuration
 317  
      */
 318  
     protected void initFromParent(HierarchicalConfiguration parentConfig)
 319  
     {
 320  238
         setExpressionEngine(parentConfig.getExpressionEngine());
 321  238
         setListDelimiter(parentConfig.getListDelimiter());
 322  238
         setDelimiterParsingDisabled(parentConfig.isDelimiterParsingDisabled());
 323  238
         setThrowExceptionOnMissing(parentConfig.isThrowExceptionOnMissing());
 324  238
     }
 325  
 
 326  
     /**
 327  
      * Performs interpolation. This implementation will ask the parent
 328  
      * configuration to perform the interpolation so that variables can be
 329  
      * evaluated in the global context.
 330  
      *
 331  
      * @param value the value to be interpolated
 332  
      */
 333  
     protected Object interpolate(Object value)
 334  
     {
 335  346
         return getParent().interpolate(value);
 336  
     }
 337  
 }