Coverage Report - org.apache.commons.configuration.interpol.ConfigurationInterpolator
 
Classes in this File Line Coverage Branch Coverage Complexity
ConfigurationInterpolator
98%
45/46
100%
11/11
2,273
 
 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. All 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://commons.apache.org/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 is 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 or that cannot be
 50  
  * resolved by their associated lookup object.
 51  
  * </p>
 52  
  * <p>
 53  
  * When a new instance of this class is created it is initialized with a default
 54  
  * set of primitive lookup objects. This set can be customized using the static
 55  
  * methods <code>registerGlobalLookup()</code> and
 56  
  * <code>deregisterGlobalLookup()</code>. Per default it contains the
 57  
  * following standard lookup objects:
 58  
  * </p>
 59  
  * <p>
 60  
  * <table border="1">
 61  
  * <tr>
 62  
  * <th>Prefix</th>
 63  
  * <th>Lookup object</th>
 64  
  * </tr>
 65  
  * <tr>
 66  
  * <td valign="top">sys</td>
 67  
  * <td>With this prefix a lookup object is associated that is able to resolve
 68  
  * system properties.</td>
 69  
  * </tr>
 70  
  * <tr>
 71  
  * <td valign="top">const</td>
 72  
  * <td>The <code>const</code> prefix indicates that a variable is to be
 73  
  * interpreted as a constant member field of a class (i.e. a field with the
 74  
  * <b>static final</b> modifiers). The name of the variable must be of the form
 75  
  * <code>&lt;full qualified class name&gt;.&lt;field name&gt;</code>, e.g.
 76  
  * <code>org.apache.commons.configuration.interpol.ConfigurationInterpolator.PREFIX_CONSTANTS
 77  
  * </code>.</td>
 78  
  * </tr>
 79  
  * </table>
 80  
  * </p>
 81  
  * <p>
 82  
  * After an instance has been created the current set of lookup objects can be
 83  
  * modified using the <code>registerLookup()</code> and
 84  
  * <code>deregisterLookup()</code> methods. The default lookup object (that is
 85  
  * invoked for variables without a prefix) can be set with the
 86  
  * <code>setDefaultLookup()</code> method. (If a
 87  
  * <code>ConfigurationInterpolator</code> instance is created by a
 88  
  * configuration object, this lookup points to the configuration itself, so that
 89  
  * variables are resolved using the configuration's properties. This ensures
 90  
  * backward compatibility to earlier version of Commons Configuration.)
 91  
  * </p>
 92  
  * <p>
 93  
  * Implementation node: Instances of this class are not thread-safe related to
 94  
  * modifications of their current set of registered lookup objects. It is
 95  
  * intended that each instance is associated with a single
 96  
  * <code>Configuration</code> object and used for its interpolation tasks.
 97  
  * </p>
 98  
  *
 99  
  * @version $Id: ConfigurationInterpolator.java 561230 2007-07-31 04:17:09Z rahul $
 100  
  * @since 1.4
 101  
  * @author <a
 102  
  * href="http://commons.apache.org/configuration/team-list.html">Commons
 103  
  * Configuration team</a>
 104  
  */
 105  
 public class ConfigurationInterpolator extends StrLookup
 106  
 {
 107  
     /**
 108  
      * Constant for the prefix of the standard lookup object for resolving
 109  
      * system properties.
 110  
      */
 111  
     public static final String PREFIX_SYSPROPERTIES = "sys";
 112  
 
 113  
     /**
 114  
      * Constant for the prefix of the standard lookup object for resolving
 115  
      * constant values.
 116  
      */
 117  
     public static final String PREFIX_CONSTANTS = "const";
 118  
 
 119  
     /** Constant for the prefix separator. */
 120  
     private static final char PREFIX_SEPARATOR = ':';
 121  
 
 122  
     /** A map with the globally registered lookup objects. */
 123  
     private static Map globalLookups;
 124  
 
 125  
     /** A map with the locally registered lookup objects. */
 126  
     private Map localLookups;
 127  
 
 128  
     /** Stores the default lookup object. */
 129  
     private StrLookup defaultLookup;
 130  
 
 131  
     /**
 132  
      * Creates a new instance of <code>ConfigurationInterpolator</code>.
 133  
      */
 134  
     public ConfigurationInterpolator()
 135  746
     {
 136  746
         synchronized (globalLookups)
 137  
         {
 138  746
             localLookups = new HashMap(globalLookups);
 139  746
         }
 140  746
     }
 141  
 
 142  
     /**
 143  
      * Registers the given lookup object for the specified prefix globally. This
 144  
      * means that all instances that are created later will use this lookup
 145  
      * object for this prefix. If for this prefix a lookup object is already
 146  
      * registered, the new lookup object will replace the old one. Note that the
 147  
      * lookup objects registered here will be shared between multiple clients.
 148  
      * So they should be thread-safe.
 149  
      *
 150  
      * @param prefix the variable prefix (must not be <b>null</b>)
 151  
      * @param lookup the lookup object to be used for this prefix (must not be
 152  
      * <b>null</b>)
 153  
      */
 154  
     public static void registerGlobalLookup(String prefix, StrLookup lookup)
 155  
     {
 156  5
         if (prefix == null)
 157  
         {
 158  1
             throw new IllegalArgumentException(
 159  
                     "Prefix for lookup object must not be null!");
 160  
         }
 161  4
         if (lookup == null)
 162  
         {
 163  1
             throw new IllegalArgumentException(
 164  
                     "Lookup object must not be null!");
 165  
         }
 166  3
         synchronized (globalLookups)
 167  
         {
 168  3
             globalLookups.put(prefix, lookup);
 169  3
         }
 170  3
     }
 171  
 
 172  
     /**
 173  
      * Deregisters the global lookup object for the specified prefix. This means
 174  
      * that this lookup object won't be available for later created instances
 175  
      * any more. For already existing instances this operation does not have any
 176  
      * impact.
 177  
      *
 178  
      * @param prefix the variable prefix
 179  
      * @return a flag whether for this prefix a lookup object had been
 180  
      * registered
 181  
      */
 182  
     public static boolean deregisterGlobalLookup(String prefix)
 183  
     {
 184  24
         synchronized (globalLookups)
 185  
         {
 186  24
             return globalLookups.remove(prefix) != null;
 187  0
         }
 188  
     }
 189  
 
 190  
     /**
 191  
      * Registers the given lookup object for the specified prefix at this
 192  
      * instance. From now on this lookup object will be used for variables that
 193  
      * have the specified prefix.
 194  
      *
 195  
      * @param prefix the variable prefix (must not be <b>null</b>)
 196  
      * @param lookup the lookup object to be used for this prefix (must not be
 197  
      * <b>null</b>)
 198  
      */
 199  
     public void registerLookup(String prefix, StrLookup lookup)
 200  
     {
 201  11
         if (prefix == null)
 202  
         {
 203  1
             throw new IllegalArgumentException(
 204  
                     "Prefix for lookup object must not be null!");
 205  
         }
 206  10
         if (lookup == null)
 207  
         {
 208  1
             throw new IllegalArgumentException(
 209  
                     "Lookup object must not be null!");
 210  
         }
 211  9
         localLookups.put(prefix, lookup);
 212  9
     }
 213  
 
 214  
     /**
 215  
      * Deregisters the lookup object for the specified prefix at this instance.
 216  
      * It will be removed from this instance.
 217  
      *
 218  
      * @param prefix the variable prefix
 219  
      * @return a flag whether for this prefix a lookup object had been
 220  
      * registered
 221  
      */
 222  
     public boolean deregisterLookup(String prefix)
 223  
     {
 224  2
         return localLookups.remove(prefix) != null;
 225  
     }
 226  
 
 227  
     /**
 228  
      * Returns a set with the prefixes, for which lookup objects are registered
 229  
      * at this instance. This means that variables with these prefixes can be
 230  
      * processed.
 231  
      *
 232  
      * @return a set with the registered variable prefixes
 233  
      */
 234  
     public Set prefixSet()
 235  
     {
 236  9
         return localLookups.keySet();
 237  
     }
 238  
 
 239  
     /**
 240  
      * Returns the default lookup object.
 241  
      *
 242  
      * @return the default lookup object
 243  
      */
 244  
     public StrLookup getDefaultLookup()
 245  
     {
 246  4764
         return defaultLookup;
 247  
     }
 248  
 
 249  
     /**
 250  
      * Sets the default lookup object. This lookup object will be used for all
 251  
      * variables without a special prefix. If it is set to <b>null</b>, such
 252  
      * variables won't be processed.
 253  
      *
 254  
      * @param defaultLookup the new default lookup object
 255  
      */
 256  
     public void setDefaultLookup(StrLookup defaultLookup)
 257  
     {
 258  724
         this.defaultLookup = defaultLookup;
 259  724
     }
 260  
 
 261  
     /**
 262  
      * Resolves the specified variable. This implementation will try to extract
 263  
      * a variable prefix from the given variable name (the first colon (':') is
 264  
      * used as prefix separator). It then passes the name of the variable with
 265  
      * the prefix stripped to the lookup object registered for this prefix. If
 266  
      * no prefix can be found or if the associated lookup object cannot resolve
 267  
      * this variable, the default lookup object will be used.
 268  
      *
 269  
      * @param var the name of the variable whose value is to be looked up
 270  
      * @return the value of this variable or <b>null</b> if it cannot be
 271  
      * resolved
 272  
      */
 273  
     public String lookup(String var)
 274  
     {
 275  2483
         if (var == null)
 276  
         {
 277  1
             return null;
 278  
         }
 279  
 
 280  2482
         int prefixPos = var.indexOf(PREFIX_SEPARATOR);
 281  2482
         if (prefixPos >= 0)
 282  
         {
 283  104
             String prefix = var.substring(0, prefixPos);
 284  104
             String name = var.substring(prefixPos + 1);
 285  104
             String value = fetchLookupForPrefix(prefix).lookup(name);
 286  104
             if (value != null)
 287  
             {
 288  99
                 return value;
 289  
             }
 290  
         }
 291  2383
         return fetchNoPrefixLookup().lookup(var);
 292  
     }
 293  
 
 294  
     /**
 295  
      * Returns the lookup object to be used for variables without a prefix. This
 296  
      * implementation will check whether a default lookup object was set. If
 297  
      * this is the case, it will be returned. Otherwise a <b>null</b> lookup
 298  
      * object will be returned.
 299  
      *
 300  
      * @return the lookup object to be used for variables without a prefix
 301  
      */
 302  
     protected StrLookup fetchNoPrefixLookup()
 303  
     {
 304  2383
         return (getDefaultLookup() != null) ? getDefaultLookup() : StrLookup.noneLookup();
 305  
     }
 306  
 
 307  
     /**
 308  
      * Obtains the lookup object for the specified prefix. This method is called
 309  
      * by the <code>lookup()</code> method. This implementation will check
 310  
      * whether a lookup object is registered for the given prefix. If not, a
 311  
      * <b>null</b> lookup object will be returned.
 312  
      *
 313  
      * @param prefix the prefix
 314  
      * @return the lookup object to be used for this prefix
 315  
      */
 316  
     protected StrLookup fetchLookupForPrefix(String prefix)
 317  
     {
 318  104
         StrLookup lookup = (StrLookup) localLookups.get(prefix);
 319  104
         if (lookup == null)
 320  
         {
 321  4
             lookup = StrLookup.noneLookup();
 322  
         }
 323  104
         return lookup;
 324  
     }
 325  
 
 326  
     // static initializer, sets up the map with the standard lookups
 327  
     static
 328  
     {
 329  55
         globalLookups = new HashMap();
 330  55
         globalLookups.put(PREFIX_SYSPROPERTIES, StrLookup.systemPropertiesLookup());
 331  55
         globalLookups.put(PREFIX_CONSTANTS, new ConstantLookup());
 332  55
     }
 333  
 }