Coverage Report - org.apache.commons.configuration.interpol.ConfigurationInterpolator
 
Classes in this File Line Coverage Branch Coverage Complexity
ConfigurationInterpolator
98%
56/57
100%
30/30
2,357
 
 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} is associated with an
 32  
  * object of this class. All interpolation tasks are delegated to this object.
 33  
  * </p>
 34  
  * <p>
 35  
  * {@code ConfigurationInterpolator} works together with the
 36  
  * {@code StrSubstitutor} class from <a
 37  
  * href="http://commons.apache.org/lang">Commons Lang</a>. By extending
 38  
  * {@code StrLookup} 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} 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} 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()} and
 56  
  * {@code deregisterGlobalLookup()}. 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} 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 <full qualified class name>.<field name>}, e.g.
 76  
  * {@code org.apache.commons.configuration.interpol.ConfigurationInterpolator.PREFIX_CONSTANTS}.
 77  
  * </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()} and
 84  
  * {@code deregisterLookup()} methods. The default lookup object (that is
 85  
  * invoked for variables without a prefix) can be set with the
 86  
  * {@code setDefaultLookup()} method. (If a
 87  
  * {@code ConfigurationInterpolator} 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} object and used for its interpolation tasks.
 97  
  * </p>
 98  
  *
 99  
  * @version $Id: ConfigurationInterpolator.java 1295276 2012-02-29 21:11:35Z oheger $
 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  
     /**
 120  
      * Constant for the prefix of the standard lookup object for resolving
 121  
      * environment properties.
 122  
      * @since 1.7
 123  
      */
 124  
     public static final String PREFIX_ENVIRONMENT = "env";
 125  
 
 126  
     /** Constant for the prefix separator. */
 127  
     private static final char PREFIX_SEPARATOR = ':';
 128  
 
 129  
     /** A map with the globally registered lookup objects. */
 130  
     private static Map<String, StrLookup> globalLookups;
 131  
 
 132  
     /** A map with the locally registered lookup objects. */
 133  
     private Map<String, StrLookup> localLookups;
 134  
 
 135  
     /** Stores the default lookup object. */
 136  
     private StrLookup defaultLookup;
 137  
 
 138  
     /** Stores a parent interpolator objects if the interpolator is nested hierarchically. */
 139  
     private ConfigurationInterpolator parentInterpolator;
 140  
 
 141  
     /**
 142  
      * Creates a new instance of {@code ConfigurationInterpolator}.
 143  
      */
 144  
     public ConfigurationInterpolator()
 145  2188
     {
 146  2188
         synchronized (globalLookups)
 147  
         {
 148  2188
             localLookups = new HashMap<String, StrLookup>(globalLookups);
 149  2188
         }
 150  2188
     }
 151  
 
 152  
     /**
 153  
      * Registers the given lookup object for the specified prefix globally. This
 154  
      * means that all instances that are created later will use this lookup
 155  
      * object for this prefix. If for this prefix a lookup object is already
 156  
      * registered, the new lookup object will replace the old one. Note that the
 157  
      * lookup objects registered here will be shared between multiple clients.
 158  
      * So they should be thread-safe.
 159  
      *
 160  
      * @param prefix the variable prefix (must not be <b>null</b>)
 161  
      * @param lookup the lookup object to be used for this prefix (must not be
 162  
      * <b>null</b>)
 163  
      */
 164  
     public static void registerGlobalLookup(String prefix, StrLookup lookup)
 165  
     {
 166  11
         if (prefix == null)
 167  
         {
 168  1
             throw new IllegalArgumentException(
 169  
                     "Prefix for lookup object must not be null!");
 170  
         }
 171  10
         if (lookup == null)
 172  
         {
 173  1
             throw new IllegalArgumentException(
 174  
                     "Lookup object must not be null!");
 175  
         }
 176  9
         synchronized (globalLookups)
 177  
         {
 178  9
             globalLookups.put(prefix, lookup);
 179  9
         }
 180  9
     }
 181  
 
 182  
     /**
 183  
      * Deregisters the global lookup object for the specified prefix. This means
 184  
      * that this lookup object won't be available for later created instances
 185  
      * any more. For already existing instances this operation does not have any
 186  
      * impact.
 187  
      *
 188  
      * @param prefix the variable prefix
 189  
      * @return a flag whether for this prefix a lookup object had been
 190  
      * registered
 191  
      */
 192  
     public static boolean deregisterGlobalLookup(String prefix)
 193  
     {
 194  24
         synchronized (globalLookups)
 195  
         {
 196  24
             return globalLookups.remove(prefix) != null;
 197  0
         }
 198  
     }
 199  
 
 200  
     /**
 201  
      * Registers the given lookup object for the specified prefix at this
 202  
      * instance. From now on this lookup object will be used for variables that
 203  
      * have the specified prefix.
 204  
      *
 205  
      * @param prefix the variable prefix (must not be <b>null</b>)
 206  
      * @param lookup the lookup object to be used for this prefix (must not be
 207  
      * <b>null</b>)
 208  
      */
 209  
     public void registerLookup(String prefix, StrLookup lookup)
 210  
     {
 211  22
         if (prefix == null)
 212  
         {
 213  1
             throw new IllegalArgumentException(
 214  
                     "Prefix for lookup object must not be null!");
 215  
         }
 216  21
         if (lookup == null)
 217  
         {
 218  1
             throw new IllegalArgumentException(
 219  
                     "Lookup object must not be null!");
 220  
         }
 221  20
         localLookups.put(prefix, lookup);
 222  20
     }
 223  
 
 224  
     /**
 225  
      * Deregisters the lookup object for the specified prefix at this instance.
 226  
      * It will be removed from this instance.
 227  
      *
 228  
      * @param prefix the variable prefix
 229  
      * @return a flag whether for this prefix a lookup object had been
 230  
      * registered
 231  
      */
 232  
     public boolean deregisterLookup(String prefix)
 233  
     {
 234  2
         return localLookups.remove(prefix) != null;
 235  
     }
 236  
 
 237  
     /**
 238  
      * Returns a set with the prefixes, for which lookup objects are registered
 239  
      * at this instance. This means that variables with these prefixes can be
 240  
      * processed.
 241  
      *
 242  
      * @return a set with the registered variable prefixes
 243  
      */
 244  
     public Set<String> prefixSet()
 245  
     {
 246  9
         return localLookups.keySet();
 247  
     }
 248  
 
 249  
     /**
 250  
      * Returns the default lookup object.
 251  
      *
 252  
      * @return the default lookup object
 253  
      */
 254  
     public StrLookup getDefaultLookup()
 255  
     {
 256  414687
         return defaultLookup;
 257  
     }
 258  
 
 259  
     /**
 260  
      * Sets the default lookup object. This lookup object will be used for all
 261  
      * variables without a special prefix. If it is set to <b>null</b>, such
 262  
      * variables won't be processed.
 263  
      *
 264  
      * @param defaultLookup the new default lookup object
 265  
      */
 266  
     public void setDefaultLookup(StrLookup defaultLookup)
 267  
     {
 268  2107
         this.defaultLookup = defaultLookup;
 269  2107
     }
 270  
 
 271  
     /**
 272  
      * Resolves the specified variable. This implementation will try to extract
 273  
      * a variable prefix from the given variable name (the first colon (':') is
 274  
      * used as prefix separator). It then passes the name of the variable with
 275  
      * the prefix stripped to the lookup object registered for this prefix. If
 276  
      * no prefix can be found or if the associated lookup object cannot resolve
 277  
      * this variable, the default lookup object will be used.
 278  
      *
 279  
      * @param var the name of the variable whose value is to be looked up
 280  
      * @return the value of this variable or <b>null</b> if it cannot be
 281  
      * resolved
 282  
      */
 283  
     @Override
 284  
     public String lookup(String var)
 285  
     {
 286  414887
         if (var == null)
 287  
         {
 288  1
             return null;
 289  
         }
 290  
 
 291  414925
         int prefixPos = var.indexOf(PREFIX_SEPARATOR);
 292  414914
         if (prefixPos >= 0)
 293  
         {
 294  413071
             String prefix = var.substring(0, prefixPos);
 295  413065
             String name = var.substring(prefixPos + 1);
 296  413048
             String value = fetchLookupForPrefix(prefix).lookup(name);
 297  413087
             if (value == null && getParentInterpolator() != null)
 298  
             {
 299  2
                 value = getParentInterpolator().lookup(name);
 300  
             }
 301  413087
             if (value != null)
 302  
             {
 303  2150
                 return value;
 304  
             }
 305  
         }
 306  412812
         String value = fetchNoPrefixLookup().lookup(var);
 307  412809
         if (value == null && getParentInterpolator() != null)
 308  
         {
 309  11
             value = getParentInterpolator().lookup(var);
 310  
         }
 311  412814
         return value;
 312  
     }
 313  
 
 314  
     /**
 315  
      * Returns the lookup object to be used for variables without a prefix. This
 316  
      * implementation will check whether a default lookup object was set. If
 317  
      * this is the case, it will be returned. Otherwise a <b>null</b> lookup
 318  
      * object will be returned (never <b>null</b>).
 319  
      *
 320  
      * @return the lookup object to be used for variables without a prefix
 321  
      */
 322  
     protected StrLookup fetchNoPrefixLookup()
 323  
     {
 324  412804
         return (getDefaultLookup() != null) ? getDefaultLookup() : StrLookup.noneLookup();
 325  
     }
 326  
 
 327  
     /**
 328  
      * Obtains the lookup object for the specified prefix. This method is called
 329  
      * by the {@code lookup()} method. This implementation will check
 330  
      * whether a lookup object is registered for the given prefix. If not, a
 331  
      * <b>null</b> lookup object will be returned (never <b>null</b>).
 332  
      *
 333  
      * @param prefix the prefix
 334  
      * @return the lookup object to be used for this prefix
 335  
      */
 336  
     protected StrLookup fetchLookupForPrefix(String prefix)
 337  
     {
 338  413043
         StrLookup lookup = localLookups.get(prefix);
 339  413025
         if (lookup == null)
 340  
         {
 341  4
             lookup = StrLookup.noneLookup();
 342  
         }
 343  413043
         return lookup;
 344  
     }
 345  
 
 346  
     /**
 347  
      * Registers the local lookup instances for the given interpolator.
 348  
      *
 349  
      * @param interpolator the instance receiving the local lookups
 350  
      * @since upcoming
 351  
      */
 352  
     public void registerLocalLookups(ConfigurationInterpolator interpolator)
 353  
     {
 354  21
         interpolator.localLookups.putAll(localLookups);
 355  21
     }
 356  
 
 357  
     /**
 358  
      * Sets the parent interpolator. This object is used if the interpolation is nested
 359  
      * hierarchically and the current interpolation object cannot resolve a variable.
 360  
      *
 361  
      * @param parentInterpolator the parent interpolator object or <b>null</b>
 362  
      * @since upcoming
 363  
      */
 364  
     public void setParentInterpolator(ConfigurationInterpolator parentInterpolator)
 365  
     {
 366  859
         this.parentInterpolator = parentInterpolator;
 367  859
     }
 368  
 
 369  
     /**
 370  
      * Requests the parent interpolator. This object is used if the interpolation is nested
 371  
      * hierarchically and the current interpolation
 372  
      *
 373  
      * @return the parent interpolator or <b>null</b>
 374  
      * @since upcoming
 375  
      */
 376  
     public ConfigurationInterpolator getParentInterpolator()
 377  
     {
 378  821925
         return this.parentInterpolator;
 379  
     }
 380  
 
 381  
     // static initializer, sets up the map with the standard lookups
 382  
     static
 383  
     {
 384  1
         globalLookups = new HashMap<String, StrLookup>();
 385  1
         globalLookups.put(PREFIX_SYSPROPERTIES, StrLookup.systemPropertiesLookup());
 386  1
         globalLookups.put(PREFIX_CONSTANTS, new ConstantLookup());
 387  1
         globalLookups.put(PREFIX_ENVIRONMENT, new EnvironmentLookup());
 388  1
     }
 389  
 }