Coverage Report - org.apache.commons.configuration.interpol.ConfigurationInterpolator
 
Classes in this File Line Coverage Branch Coverage Complexity
ConfigurationInterpolator
98%
43/44
100%
10/10
2,182
 
 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.interpol;
 18  
 
 19  
 import java.util.HashMap;
 20  
 import java.util.Map;
 21  
 import java.util.Set;
 22  
 
 23  
 import org.apache.commons.lang.text.StrLookup;
 24  
 
 25  
 /**
 26  
  * <p>
 27  
  * A class that handles interpolation (variable substitution) for configuration
 28  
  * objects.
 29  
  * </p>
 30  
  * <p>
 31  
  * Each instance of <code>AbstractConfiguration</code> is associated with an
 32  
  * object of this class. Each interpolation tasks are delegated to this object.
 33  
  * </p>
 34  
  * <p>
 35  
  * <code>ConfigurationInterpolator</code> works together with the
 36  
  * <code>StrSubstitutor</code> class from <a
 37  
  * href="http://jakarta.apache.org/commons/lang">Commons Lang</a>. By extending
 38  
  * <code>StrLookup</code> it is able to provide values for variables that
 39  
  * appear in expressions.
 40  
  * </p>
 41  
  * <p>
 42  
  * The basic idea of this class is that it can maintain a set of primitive
 43  
  * <code>StrLookup</code> objects, each of which are identified by a special
 44  
  * prefix. The variables to be processed have the form
 45  
  * <code>${prefix:name}</code>. <code>ConfigurationInterpolator</code> will
 46  
  * extract the prefix and determine, which primitive lookup object is registered
 47  
  * for it. Then the name of the variable is passed to this object to obtain the
 48  
  * actual value. It is also possible to define a default lookup object, which
 49  
  * will be used for variables that do not have a prefix.
 50  
  * </p>
 51  
  * <p>
 52  
  * When a new instance of this class is created it is initialized with a default
 53  
  * set of primitive lookup objects. This set can be customized using the static
 54  
  * methods <code>registerGlobalLookup()</code> and
 55  
  * <code>deregisterGlobalLookup()</code>. Per default it contains the
 56  
  * following standard lookup objects:
 57  
  * </p>
 58  
  * <p>
 59  
  * <table border="1">
 60  
  * <tr>
 61  
  * <th>Prefix</th>
 62  
  * <th>Lookup object</th>
 63  
  * </tr>
 64  
  * <tr>
 65  
  * <td valign="top">sys</td>
 66  
  * <td>With this prefix a lookup object is associated that is able to resolve
 67  
  * system properties.</td>
 68  
  * </tr>
 69  
  * <tr>
 70  
  * <td valign="top">const</td>
 71  
  * <td>The <code>const</code> prefix indicates that a variable is to be
 72  
  * interpreted as a constant member field of a class (i.e. a field with the
 73  
  * <b>static final</b> modifiers). The name of the variable must be of the form
 74  
  * <code>&lt;full qualified class name&gt;.&lt;field name&gt;</code>, e.g.
 75  
  * <code>org.apache.commons.configuration.interpol.ConfigurationInterpolator.PREFIX_CONSTANTS
 76  
  * </code>.</td>
 77  
  * </tr>
 78  
  * </table>
 79  
  * </p>
 80  
  * <p>
 81  
  * After an instance has been created the current set of lookup objects can be
 82  
  * modified using the <code>registerLookup()</code> and
 83  
  * <code>deregisterLookup()</code> methods. The default lookup object (that is
 84  
  * invoked for variables without a prefix) can be set with the
 85  
  * <code>setDefaultLookup()</code> method. (If a
 86  
  * <code>ConfigurationInterpolator</code> instance is created by a
 87  
  * configuration object, this lookup points to the configuration itself, so that
 88  
  * variables are resolved using the configuration's properties. This ensures
 89  
  * backward compatibility to earlier version of Commons Configuration.)
 90  
  * </p>
 91  
  * <p>
 92  
  * Implementation node: Instances of this class are not thread-safe related to
 93  
  * modifications of their current set of registered lookup objects. It is
 94  
  * intended that each instance is associated with a single
 95  
  * <code>Configuration</conde>
 96  
  * object and used for its interpolation tasks.</p>
 97  
  *
 98  
  * @version $Id: ConfigurationInterpolator.java 491243 2006-12-30 16:04:03Z oheger $
 99  
  * @since 1.4
 100  
  * @author <a
 101  
  * href="http://jakarta.apache.org/commons/configuration/team-list.html">Commons
 102  
  * Configuration team</a>
 103  
  */
 104  
 public class ConfigurationInterpolator extends StrLookup
 105  
 {
 106  
     /**
 107  
      * Constant for the prefix of the standard lookup object for resolving
 108  
      * system properties.
 109  
      */
 110  
     public static final String PREFIX_SYSPROPERTIES = "sys";
 111  
 
 112  
     /**
 113  
      * Constant for the prefix of the standard lookup object for resolving
 114  
      * constant values.
 115  
      */
 116  
     public static final String PREFIX_CONSTANTS = "const";
 117  
 
 118  
     /** Constant for the prefix separator. */
 119  
     private static final char PREFIX_SEPARATOR = ':';
 120  
 
 121  
     /** A map with the globally registered lookup objects. */
 122  
     private static Map globalLookups;
 123  
 
 124  
     /** A map with the locally registered lookup objects. */
 125  
     private Map localLookups;
 126  
 
 127  
     /** Stores the default lookup object. */
 128  
     private StrLookup defaultLookup;
 129  
 
 130  
     /**
 131  
      * Creates a new instance of <code>ConfigurationInterpolator</code>.
 132  
      */
 133  
     public ConfigurationInterpolator()
 134  475
     {
 135  475
         synchronized (globalLookups)
 136  
         {
 137  475
             localLookups = new HashMap(globalLookups);
 138  475
         }
 139  475
     }
 140  
 
 141  
     /**
 142  
      * Registers the given lookup object for the specified prefix globally. This
 143  
      * means that all instances that are created later will use this lookup
 144  
      * object for this prefix. If for this prefix a lookup object is already
 145  
      * registered, the new lookup object will replace the old one. Note that the
 146  
      * lookup objects registered here will be shared between multiple clients.
 147  
      * So they should be thread-safe.
 148  
      *
 149  
      * @param prefix the variable prefix (must not be <b>null</b>)
 150  
      * @param lookup the lookup object to be used for this prefix (must not be
 151  
      * <b>null</b>)
 152  
      */
 153  
     public static void registerGlobalLookup(String prefix, StrLookup lookup)
 154  
     {
 155  4
         if (prefix == null)
 156  
         {
 157  1
             throw new IllegalArgumentException(
 158  
                     "Prefix for lookup object must not be null!");
 159  
         }
 160  3
         if (lookup == null)
 161  
         {
 162  1
             throw new IllegalArgumentException(
 163  
                     "Lookup object must not be null!");
 164  
         }
 165  2
         synchronized (globalLookups)
 166  
         {
 167  2
             globalLookups.put(prefix, lookup);
 168  2
         }
 169  2
     }
 170  
 
 171  
     /**
 172  
      * Deregisters the global lookup object for the specified prefix. This means
 173  
      * that this lookup object won't be available for later created instances
 174  
      * any more. For already existing instances this operation does not have any
 175  
      * impact.
 176  
      *
 177  
      * @param prefix the variable prefix
 178  
      * @return a flag whether for this prefix a lookup object had been
 179  
      * registered
 180  
      */
 181  
     public static boolean deregisterGlobalLookup(String prefix)
 182  
     {
 183  23
         synchronized (globalLookups)
 184  
         {
 185  23
             return globalLookups.remove(prefix) != null;
 186  0
         }
 187  
     }
 188  
 
 189  
     /**
 190  
      * Registers the given lookup object for the specified prefix at this
 191  
      * instance. From now on this lookup object will be used for variables that
 192  
      * have the specified prefix.
 193  
      *
 194  
      * @param prefix the variable prefix (must not be <b>null</b>)
 195  
      * @param lookup the lookup object to be used for this prefix (must not be
 196  
      * <b>null</b>)
 197  
      */
 198  
     public void registerLookup(String prefix, StrLookup lookup)
 199  
     {
 200  9
         if (prefix == null)
 201  
         {
 202  1
             throw new IllegalArgumentException(
 203  
                     "Prefix for lookup object must not be null!");
 204  
         }
 205  8
         if (lookup == null)
 206  
         {
 207  1
             throw new IllegalArgumentException(
 208  
                     "Lookup object must not be null!");
 209  
         }
 210  7
         localLookups.put(prefix, lookup);
 211  7
     }
 212  
 
 213  
     /**
 214  
      * Deregisters the lookup object for the specified prefix at this instance.
 215  
      * It will be removed from this instance.
 216  
      *
 217  
      * @param prefix the variable prefix
 218  
      * @return a flag whether for this prefix a lookup object had been
 219  
      * registered
 220  
      */
 221  
     public boolean deregisterLookup(String prefix)
 222  
     {
 223  2
         return localLookups.remove(prefix) != null;
 224  
     }
 225  
 
 226  
     /**
 227  
      * Returns a set with the prefixes, for which lookup objects are registered
 228  
      * at this instance. This means that variables with these prefixes can be
 229  
      * processed.
 230  
      *
 231  
      * @return a set with the registered variable prefixes
 232  
      */
 233  
     public Set prefixSet()
 234  
     {
 235  9
         return localLookups.keySet();
 236  
     }
 237  
 
 238  
     /**
 239  
      * Returns the default lookup object.
 240  
      *
 241  
      * @return the default lookup object
 242  
      */
 243  
     public StrLookup getDefaultLookup()
 244  
     {
 245  276
         return defaultLookup;
 246  
     }
 247  
 
 248  
     /**
 249  
      * Sets the default lookup object. This lookup object will be used for all
 250  
      * variables without a special prefix. If it is set to <b>null</b>, such
 251  
      * variables won't be processed.
 252  
      *
 253  
      * @param defaultLookup the new default lookup object
 254  
      */
 255  
     public void setDefaultLookup(StrLookup defaultLookup)
 256  
     {
 257  453
         this.defaultLookup = defaultLookup;
 258  453
     }
 259  
 
 260  
     /**
 261  
      * Resolves the specified variable. This implementation will try to extract
 262  
      * a variable prefix from the given variable name (the first colon (':') is
 263  
      * used as prefix separator). It then passes the name of the variable with
 264  
      * the prefix stripped to the lookup object registered for this prefix. If
 265  
      * no prefix can be found, the default lookup object will be used.
 266  
      *
 267  
      * @param var the name of the variable whose value is to be looked up
 268  
      * @return the value of this variable or <b>null</b> if it cannot be
 269  
      * resolved
 270  
      */
 271  
     public String lookup(String var)
 272  
     {
 273  204
         if (var == null)
 274  
         {
 275  1
             return null;
 276  
         }
 277  
 
 278  203
         int prefixPos = var.indexOf(PREFIX_SEPARATOR);
 279  203
         if (prefixPos < 0)
 280  
         {
 281  138
             return fetchNoPrefixLookup().lookup(var);
 282  
         }
 283  
         else
 284  
         {
 285  65
             String prefix = var.substring(0, prefixPos);
 286  65
             String name = var.substring(prefixPos + 1);
 287  65
             return fetchLookupForPrefix(prefix).lookup(name);
 288  
         }
 289  
     }
 290  
 
 291  
     /**
 292  
      * Returns the lookup object to be used for variables without a prefix. This
 293  
      * implementation will check whether a default lookup object was set. If
 294  
      * this is the case, it will be returned. Otherwise a <b>null</b> lookup
 295  
      * object will be returned.
 296  
      *
 297  
      * @return the lookup object to be used for variables without a prefix
 298  
      */
 299  
     protected StrLookup fetchNoPrefixLookup()
 300  
     {
 301  138
         return (getDefaultLookup() != null) ? getDefaultLookup() : StrLookup
 302  
                 .noneLookup();
 303  
     }
 304  
 
 305  
     /**
 306  
      * Obtains the lookup object for the specified prefix. This method is called
 307  
      * by the <code>lookup()</code> method. This implementation will check
 308  
      * whether a lookup object is registered for the given prefix. If not, a
 309  
      * <b>null</b> lookup object will be returned.
 310  
      *
 311  
      * @param prefix the prefix
 312  
      * @return the lookup object to be used for this prefix
 313  
      */
 314  
     protected StrLookup fetchLookupForPrefix(String prefix)
 315  
     {
 316  65
         StrLookup lookup = (StrLookup) localLookups.get(prefix);
 317  65
         if (lookup == null)
 318  
         {
 319  2
             lookup = StrLookup.noneLookup();
 320  
         }
 321  65
         return lookup;
 322  
     }
 323  
 
 324  
     // static initializer, sets up the map with the standard lookups
 325  
     static
 326  48
     {
 327  48
         globalLookups = new HashMap();
 328  48
         globalLookups.put(PREFIX_SYSPROPERTIES, StrLookup
 329  
                 .systemPropertiesLookup());
 330  48
         globalLookups.put(PREFIX_CONSTANTS, new ConstantLookup());
 331  
     }
 332  
 }