001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package org.apache.commons.configuration2.builder; 018 019import java.util.Collection; 020import java.util.Collections; 021import java.util.HashMap; 022import java.util.Map; 023 024import org.apache.commons.configuration2.ConfigurationUtils; 025import org.apache.commons.configuration2.ImmutableConfiguration; 026import org.apache.commons.configuration2.Initializable; 027import org.apache.commons.configuration2.beanutils.BeanDeclaration; 028import org.apache.commons.configuration2.beanutils.BeanHelper; 029import org.apache.commons.configuration2.beanutils.ConstructorArg; 030import org.apache.commons.configuration2.event.Event; 031import org.apache.commons.configuration2.event.EventListener; 032import org.apache.commons.configuration2.event.EventListenerList; 033import org.apache.commons.configuration2.event.EventListenerRegistrationData; 034import org.apache.commons.configuration2.event.EventSource; 035import org.apache.commons.configuration2.event.EventType; 036import org.apache.commons.configuration2.ex.ConfigurationException; 037import org.apache.commons.configuration2.ex.ConfigurationRuntimeException; 038import org.apache.commons.configuration2.reloading.ReloadingController; 039 040/** 041 * <p> 042 * An implementation of the {@code ConfigurationBuilder} interface which is able to create different concrete 043 * {@code ImmutableConfiguration} implementations based on reflection. 044 * </p> 045 * <p> 046 * When constructing an instance of this class the concrete {@code ImmutableConfiguration} implementation class has to 047 * be provided. Then properties for the new {@code ImmutableConfiguration} instance can be set. The first call to 048 * {@code getConfiguration()} creates and initializes the new {@code ImmutableConfiguration} object. It is cached and 049 * returned by subsequent calls. This cache - and also the initialization properties set so far - can be flushed by 050 * calling one of the {@code reset()} methods. That way other {@code ImmutableConfiguration} instances with different 051 * properties can be created. 052 * </p> 053 * <p> 054 * If the newly created {@code ImmutableConfiguration} object implements the {@code Initializable} interface, its 055 * {@code initialize()} method is called after all initialization properties have been set. This way a concrete 056 * implementation class can perform arbitrary initialization steps. 057 * </p> 058 * <p> 059 * There are multiple options for setting up a {@code BasicConfigurationBuilder} instance: 060 * </p> 061 * <ul> 062 * <li>All initialization properties can be set in one or multiple calls of the {@code configure()} method. In each call 063 * an arbitrary number of {@link BuilderParameters} objects can be passed. The API allows method chaining and is 064 * intended to be used from Java code.</li> 065 * <li>If builder instances are created by other means - e.g. using a dependency injection framework -, the fluent API 066 * approach may not be suitable. For those use cases it is also possible to pass in all initialization parameters as a 067 * map. The keys of the map have to match initialization properties of the {@code ImmutableConfiguration} object to be 068 * created, the values are the corresponding property values. For instance, the key <em>throwExceptionOnMissing</em> in 069 * the map will cause the method {@code setThrowExceptionOnMissing()} on the {@code ImmutableConfiguration} object to be 070 * called with the corresponding value as parameter.</li> 071 * </ul> 072 * <p> 073 * A builder instance can be constructed with an <em>allowFailOnInit</em> flag. If set to <strong>true</strong>, 074 * exceptions during initialization of the configuration are ignored; in such a case an empty configuration object is 075 * returned. A use case for this flag is a scenario in which a configuration is optional and created on demand the first 076 * time configuration data is to be stored. Consider an application that stores user-specific configuration data in the 077 * user's home directory: When started for the first time by a new user there is no configuration file; so it makes 078 * sense to start with an empty configuration object. On application exit, settings can be stored in this object and 079 * written to the associated file. Then they are available on next application start. 080 * </p> 081 * <p> 082 * This class is thread-safe. Multiple threads can modify initialization properties and call {@code getConfiguration()}. 083 * However, the intended use case is that the builder is configured by a single thread first. Then 084 * {@code getConfiguration()} can be called concurrently, and it is guaranteed that always the same 085 * {@code ImmutableConfiguration} instance is returned until the builder is reset. 086 * </p> 087 * 088 * @since 2.0 089 * @param <T> the concrete type of {@code ImmutableConfiguration} objects created by this builder 090 */ 091public class BasicConfigurationBuilder<T extends ImmutableConfiguration> implements ConfigurationBuilder<T> { 092 /** The class of the objects produced by this builder instance. */ 093 private final Class<? extends T> resultClass; 094 095 /** An object managing the event listeners registered at this builder. */ 096 private final EventListenerList eventListeners; 097 098 /** A flag whether exceptions on initializing configurations are allowed. */ 099 private final boolean allowFailOnInit; 100 101 /** The map with current initialization parameters. */ 102 private Map<String, Object> parameters; 103 104 /** The current bean declaration. */ 105 private BeanDeclaration resultDeclaration; 106 107 /** The result object of this builder. */ 108 private volatile T result; 109 110 /** 111 * Creates a new instance of {@code BasicConfigurationBuilder} and initializes it with the given result class. No 112 * initialization properties are set. 113 * 114 * @param resCls the result class (must not be <b>null</b>) 115 * @throws IllegalArgumentException if the result class is <b>null</b> 116 */ 117 public BasicConfigurationBuilder(final Class<? extends T> resCls) { 118 this(resCls, null); 119 } 120 121 /** 122 * Creates a new instance of {@code BasicConfigurationBuilder} and initializes it with the given result class and an 123 * initial set of builder parameters. The <em>allowFailOnInit</em> flag is set to <strong>false</strong>. 124 * 125 * @param resCls the result class (must not be <b>null</b>) 126 * @param params a map with initialization parameters 127 * @throws IllegalArgumentException if the result class is <b>null</b> 128 */ 129 public BasicConfigurationBuilder(final Class<? extends T> resCls, final Map<String, Object> params) { 130 this(resCls, params, false); 131 } 132 133 /** 134 * Creates a new instance of {@code BasicConfigurationBuilder} and initializes it with the given result class, an 135 * initial set of builder parameters, and the <em>allowFailOnInit</em> flag. The map with parameters may be <b>null</b>, 136 * in this case no initialization parameters are set. 137 * 138 * @param resCls the result class (must not be <b>null</b>) 139 * @param params a map with initialization parameters 140 * @param allowFailOnInit a flag whether exceptions on initializing a newly created {@code ImmutableConfiguration} 141 * object are allowed 142 * @throws IllegalArgumentException if the result class is <b>null</b> 143 */ 144 public BasicConfigurationBuilder(final Class<? extends T> resCls, final Map<String, Object> params, final boolean allowFailOnInit) { 145 if (resCls == null) { 146 throw new IllegalArgumentException("Result class must not be null!"); 147 } 148 149 resultClass = resCls; 150 this.allowFailOnInit = allowFailOnInit; 151 eventListeners = new EventListenerList(); 152 updateParameters(params); 153 } 154 155 /** 156 * Gets the result class of this builder. The objects produced by this builder have the class returned here. 157 * 158 * @return the result class of this builder 159 */ 160 public Class<? extends T> getResultClass() { 161 return resultClass; 162 } 163 164 /** 165 * Returns the <em>allowFailOnInit</em> flag. See the header comment for information about this flag. 166 * 167 * @return the <em>allowFailOnInit</em> flag 168 */ 169 public boolean isAllowFailOnInit() { 170 return allowFailOnInit; 171 } 172 173 /** 174 * Sets the initialization parameters of this builder. Already existing parameters are replaced by the content of the 175 * given map. 176 * 177 * @param params the new initialization parameters of this builder; can be <b>null</b>, then all initialization 178 * parameters are removed 179 * @return a reference to this builder for method chaining 180 */ 181 public synchronized BasicConfigurationBuilder<T> setParameters(final Map<String, Object> params) { 182 updateParameters(params); 183 return this; 184 } 185 186 /** 187 * Adds the content of the given map to the already existing initialization parameters. 188 * 189 * @param params the map with additional initialization parameters; may be <b>null</b>, then this call has no effect 190 * @return a reference to this builder for method chaining 191 */ 192 public synchronized BasicConfigurationBuilder<T> addParameters(final Map<String, Object> params) { 193 final Map<String, Object> newParams = new HashMap<>(getParameters()); 194 if (params != null) { 195 newParams.putAll(params); 196 } 197 updateParameters(newParams); 198 return this; 199 } 200 201 /** 202 * Appends the content of the specified {@code BuilderParameters} objects to the current initialization parameters. 203 * Calling this method multiple times will create a union of the parameters provided. 204 * 205 * @param params an arbitrary number of objects with builder parameters 206 * @return a reference to this builder for method chaining 207 * @throws NullPointerException if a <b>null</b> array is passed 208 */ 209 public BasicConfigurationBuilder<T> configure(final BuilderParameters... params) { 210 final Map<String, Object> newParams = new HashMap<>(); 211 for (final BuilderParameters p : params) { 212 newParams.putAll(p.getParameters()); 213 handleEventListenerProviders(p); 214 } 215 return setParameters(newParams); 216 } 217 218 /** 219 * {@inheritDoc} This implementation creates the result configuration on first access. Later invocations return the same 220 * object until this builder is reset. The double-check idiom for lazy initialization is used (Bloch, Effective Java, 221 * item 71). 222 */ 223 @Override 224 public T getConfiguration() throws ConfigurationException { 225 fireBuilderEvent(new ConfigurationBuilderEvent(this, ConfigurationBuilderEvent.CONFIGURATION_REQUEST)); 226 227 T resObj = result; 228 boolean created = false; 229 if (resObj == null) { 230 synchronized (this) { 231 resObj = result; 232 if (resObj == null) { 233 result = resObj = createResult(); 234 created = true; 235 } 236 } 237 } 238 239 if (created) { 240 fireBuilderEvent(new ConfigurationBuilderResultCreatedEvent(this, ConfigurationBuilderResultCreatedEvent.RESULT_CREATED, resObj)); 241 } 242 return resObj; 243 } 244 245 /** 246 * {@inheritDoc} This implementation also takes care that the event listener is added to the managed configuration 247 * object. 248 * 249 * @throws IllegalArgumentException if the event type or the listener is <b>null</b> 250 */ 251 @Override 252 public <E extends Event> void addEventListener(final EventType<E> eventType, final EventListener<? super E> listener) { 253 installEventListener(eventType, listener); 254 } 255 256 /** 257 * {@inheritDoc} This implementation also takes care that the event listener is removed from the managed configuration 258 * object. 259 */ 260 @Override 261 public <E extends Event> boolean removeEventListener(final EventType<E> eventType, final EventListener<? super E> listener) { 262 fetchEventSource().removeEventListener(eventType, listener); 263 return eventListeners.removeEventListener(eventType, listener); 264 } 265 266 /** 267 * Clears an existing result object. An invocation of this method causes a new {@code ImmutableConfiguration} object to 268 * be created the next time {@link #getConfiguration()} is called. 269 */ 270 public void resetResult() { 271 final T oldResult; 272 synchronized (this) { 273 oldResult = result; 274 result = null; 275 resultDeclaration = null; 276 } 277 278 if (oldResult != null) { 279 removeEventListeners(oldResult); 280 } 281 fireBuilderEvent(new ConfigurationBuilderEvent(this, ConfigurationBuilderEvent.RESET)); 282 } 283 284 /** 285 * Removes all initialization parameters of this builder. This method can be called if this builder is to be reused for 286 * creating result objects with a different configuration. 287 */ 288 public void resetParameters() { 289 setParameters(null); 290 } 291 292 /** 293 * Resets this builder. This is a convenience method which combines calls to {@link #resetResult()} and 294 * {@link #resetParameters()}. 295 */ 296 public synchronized void reset() { 297 resetParameters(); 298 resetResult(); 299 } 300 301 /** 302 * Connects this builder with a {@code ReloadingController}. With this method support for reloading can be added to an 303 * arbitrary builder object. Event listeners are registered at the reloading controller and this builder with connect 304 * both objects: 305 * <ul> 306 * <li>When the reloading controller detects that a reload is required, the builder's {@link #resetResult()} method is 307 * called; so the managed result object is invalidated.</li> 308 * <li>When a new result object has been created the controller's reloading state is reset, so that new changes can be 309 * detected again.</li> 310 * </ul> 311 * 312 * @param controller the {@code ReloadingController} to connect to (must not be <b>null</b>) 313 * @throws IllegalArgumentException if the controller is <b>null</b> 314 */ 315 public final void connectToReloadingController(final ReloadingController controller) { 316 if (controller == null) { 317 throw new IllegalArgumentException("ReloadingController must not be null!"); 318 } 319 ReloadingBuilderSupportListener.connect(this, controller); 320 } 321 322 /** 323 * Creates a new, initialized result object. This method is called by {@code getConfiguration()} if no valid result 324 * object exists. This base implementation performs two steps: 325 * <ul> 326 * <li>{@code createResultInstance()} is called to create a new, uninitialized result object.</li> 327 * <li>{@code initResultInstance()} is called to process all initialization parameters.</li> 328 * </ul> 329 * It also evaluates the <em>allowFailOnInit</em> flag, i.e. if initialization causes an exception and this flag is set, 330 * the exception is ignored, and the newly created, uninitialized configuration is returned. Note that this method is 331 * called in a synchronized block. 332 * 333 * @return the newly created result object 334 * @throws ConfigurationException if an error occurs 335 */ 336 protected T createResult() throws ConfigurationException { 337 final T resObj = createResultInstance(); 338 339 try { 340 initResultInstance(resObj); 341 } catch (final ConfigurationException cex) { 342 if (!isAllowFailOnInit()) { 343 throw cex; 344 } 345 } 346 347 return resObj; 348 } 349 350 /** 351 * Creates the new, uninitialized result object. This is the first step of the process of producing a result object for 352 * this builder. This implementation uses the {@link BeanHelper} class to create a new object based on the 353 * {@link BeanDeclaration} returned by {@link #getResultDeclaration()}. Note: This method is invoked in a synchronized 354 * block. 355 * 356 * @return the newly created, yet uninitialized result object 357 * @throws ConfigurationException if an exception occurs 358 */ 359 protected T createResultInstance() throws ConfigurationException { 360 final Object bean = fetchBeanHelper().createBean(getResultDeclaration()); 361 checkResultInstance(bean); 362 return getResultClass().cast(bean); 363 } 364 365 /** 366 * Initializes a newly created result object. This is the second step of the process of producing a result object for 367 * this builder. This implementation uses the {@link BeanHelper} class to initialize the object's property based on the 368 * {@link BeanDeclaration} returned by {@link #getResultDeclaration()}. Note: This method is invoked in a synchronized 369 * block. This is required because internal state is accessed. Sub classes must not call this method without proper 370 * synchronization. 371 * 372 * @param obj the object to be initialized 373 * @throws ConfigurationException if an error occurs 374 */ 375 protected void initResultInstance(final T obj) throws ConfigurationException { 376 fetchBeanHelper().initBean(obj, getResultDeclaration()); 377 registerEventListeners(obj); 378 handleInitializable(obj); 379 } 380 381 /** 382 * Gets the {@code BeanDeclaration} that is used to create and initialize result objects. The declaration is created 383 * on first access (by invoking {@link #createResultDeclaration(Map)}) based on the current initialization parameters. 384 * 385 * @return the {@code BeanDeclaration} for dynamically creating a result object 386 * @throws ConfigurationException if an error occurs 387 */ 388 protected final synchronized BeanDeclaration getResultDeclaration() throws ConfigurationException { 389 if (resultDeclaration == null) { 390 resultDeclaration = createResultDeclaration(getFilteredParameters()); 391 } 392 return resultDeclaration; 393 } 394 395 /** 396 * Gets a (unmodifiable) map with the current initialization parameters set for this builder. The map is populated 397 * with the parameters set using the various configuration options. 398 * 399 * @return a map with the current set of initialization parameters 400 */ 401 protected final synchronized Map<String, Object> getParameters() { 402 if (parameters != null) { 403 return parameters; 404 } 405 return Collections.emptyMap(); 406 } 407 408 /** 409 * Obtains the {@code BeanHelper} object to be used when dealing with bean declarations. This method checks whether this 410 * builder was configured with a specific {@code BeanHelper} instance. If so, this instance is used. Otherwise, the 411 * default {@code BeanHelper} is returned. 412 * 413 * @return the {@code BeanHelper} to be used 414 */ 415 protected final BeanHelper fetchBeanHelper() { 416 final BeanHelper helper = BasicBuilderParameters.fetchBeanHelper(getParameters()); 417 return helper != null ? helper : BeanHelper.INSTANCE; 418 } 419 420 /** 421 * Creates a new {@code BeanDeclaration} which is used for creating new result objects dynamically. This implementation 422 * creates a specialized {@code BeanDeclaration} object that is initialized from the given map of initialization 423 * parameters. The {@code BeanDeclaration} must be initialized with the result class of this builder, otherwise 424 * exceptions will be thrown when the result object is created. Note: This method is invoked in a synchronized block. 425 * 426 * @param params a snapshot of the current initialization parameters 427 * @return the {@code BeanDeclaration} for creating result objects 428 * @throws ConfigurationException if an error occurs 429 */ 430 protected BeanDeclaration createResultDeclaration(final Map<String, Object> params) throws ConfigurationException { 431 return new BeanDeclaration() { 432 @Override 433 public Map<String, Object> getNestedBeanDeclarations() { 434 // no nested beans 435 return Collections.emptyMap(); 436 } 437 438 @Override 439 public Collection<ConstructorArg> getConstructorArgs() { 440 // no constructor arguments 441 return Collections.emptySet(); 442 } 443 444 @Override 445 public Map<String, Object> getBeanProperties() { 446 // the properties are equivalent to the parameters 447 return params; 448 } 449 450 @Override 451 public Object getBeanFactoryParameter() { 452 return null; 453 } 454 455 @Override 456 public String getBeanFactoryName() { 457 return null; 458 } 459 460 @Override 461 public String getBeanClassName() { 462 return getResultClass().getName(); 463 } 464 }; 465 } 466 467 /** 468 * Copies all {@code EventListener} objects registered at this builder to the specified target configuration builder. 469 * This method is intended to be used by derived classes which support inheritance of their properties to other builder 470 * objects. 471 * 472 * @param target the target configuration builder (must not be <b>null</b>) 473 * @throws NullPointerException if the target builder is <b>null</b> 474 */ 475 protected synchronized void copyEventListeners(final BasicConfigurationBuilder<?> target) { 476 copyEventListeners(target, eventListeners); 477 } 478 479 /** 480 * Copies all event listeners in the specified list to the specified target configuration builder. This method is 481 * intended to be used by derived classes which have to deal with managed configuration builders that need to be 482 * initialized with event listeners. 483 * 484 * @param target the target configuration builder (must not be <b>null</b>) 485 * @param listeners the event listeners to be copied over 486 * @throws NullPointerException if the target builder is <b>null</b> 487 */ 488 protected void copyEventListeners(final BasicConfigurationBuilder<?> target, final EventListenerList listeners) { 489 target.eventListeners.addAll(listeners); 490 } 491 492 /** 493 * Adds the specified event listener to this object. This method is called by {@code addEventListener()}, it does the 494 * actual listener registration. Because it is final it can be called by sub classes in the constructor if there is 495 * already the need to register an event listener. 496 * 497 * @param eventType the event type object 498 * @param listener the listener to be registered 499 * @param <E> the event type 500 */ 501 protected final <E extends Event> void installEventListener(final EventType<E> eventType, final EventListener<? super E> listener) { 502 fetchEventSource().addEventListener(eventType, listener); 503 eventListeners.addEventListener(eventType, listener); 504 } 505 506 /** 507 * Sends the specified builder event to all registered listeners. 508 * 509 * @param event the event to be fired 510 */ 511 protected void fireBuilderEvent(final ConfigurationBuilderEvent event) { 512 eventListeners.fire(event); 513 } 514 515 /** 516 * Replaces the current map with parameters by a new one. 517 * 518 * @param newParams the map with new parameters (may be <b>null</b>) 519 */ 520 private void updateParameters(final Map<String, Object> newParams) { 521 final Map<String, Object> map = new HashMap<>(); 522 if (newParams != null) { 523 map.putAll(newParams); 524 } 525 parameters = Collections.unmodifiableMap(map); 526 } 527 528 /** 529 * Registers the available event listeners at the given object. This method is called for each result object created by 530 * the builder. 531 * 532 * @param obj the object to initialize 533 */ 534 private void registerEventListeners(final T obj) { 535 final EventSource evSrc = ConfigurationUtils.asEventSource(obj, true); 536 eventListeners.getRegistrations().forEach(regData -> registerListener(evSrc, regData)); 537 } 538 539 /** 540 * Removes all available event listeners from the given result object. This method is called when the result of this 541 * builder is reset. Then the old managed configuration should no longer generate events. 542 * 543 * @param obj the affected result object 544 */ 545 private void removeEventListeners(final T obj) { 546 final EventSource evSrc = ConfigurationUtils.asEventSource(obj, true); 547 eventListeners.getRegistrations().forEach(regData -> removeListener(evSrc, regData)); 548 } 549 550 /** 551 * Returns an {@code EventSource} for the current result object. If there is no current result or if it does not extend 552 * {@code EventSource}, a dummy event source is returned. 553 * 554 * @return the {@code EventSource} for the current result object 555 */ 556 private EventSource fetchEventSource() { 557 return ConfigurationUtils.asEventSource(result, true); 558 } 559 560 /** 561 * Checks whether the specified parameters object implements the {@code EventListenerProvider} interface. If so, the 562 * event listeners it provides are added to this builder. 563 * 564 * @param params the parameters object 565 */ 566 private void handleEventListenerProviders(final BuilderParameters params) { 567 if (params instanceof EventListenerProvider) { 568 eventListeners.addAll(((EventListenerProvider) params).getListeners()); 569 } 570 } 571 572 /** 573 * Checks whether the class of the result configuration is compatible with this builder's result class. This is done to 574 * ensure that only objects of the expected result class are created. 575 * 576 * @param inst the result instance to be checked 577 * @throws ConfigurationRuntimeException if an invalid result class is detected 578 */ 579 private void checkResultInstance(final Object inst) { 580 if (!getResultClass().isInstance(inst)) { 581 throw new ConfigurationRuntimeException("Incompatible result object: " + inst); 582 } 583 } 584 585 /** 586 * Gets a map with initialization parameters where all parameters starting with the reserved prefix have been 587 * filtered out. 588 * 589 * @return the filtered parameters map 590 */ 591 private Map<String, Object> getFilteredParameters() { 592 final Map<String, Object> filteredMap = new HashMap<>(getParameters()); 593 filteredMap.keySet().removeIf(key -> key.startsWith(BuilderParameters.RESERVED_PARAMETER_PREFIX)); 594 return filteredMap; 595 } 596 597 /** 598 * Performs special initialization of the result object. This method is called after parameters have been set on a newly 599 * created result instance. If supported by the result class, the {@code initialize()} method is now called. 600 * 601 * @param obj the newly created result object 602 */ 603 private void handleInitializable(final T obj) { 604 if (obj instanceof Initializable) { 605 ((Initializable) obj).initialize(); 606 } 607 } 608 609 /** 610 * Registers an event listener at an event source object. 611 * 612 * @param evSrc the event source 613 * @param regData the registration data object 614 * @param <E> the type of the event listener 615 */ 616 private static <E extends Event> void registerListener(final EventSource evSrc, final EventListenerRegistrationData<E> regData) { 617 evSrc.addEventListener(regData.getEventType(), regData.getListener()); 618 } 619 620 /** 621 * Removes an event listener from an event source object. 622 * 623 * @param evSrc the event source 624 * @param regData the registration data object 625 * @param <E> the type of the event listener 626 */ 627 private static <E extends Event> void removeListener(final EventSource evSrc, final EventListenerRegistrationData<E> regData) { 628 evSrc.removeEventListener(regData.getEventType(), regData.getListener()); 629 } 630}