DefaultParametersManager.java
- /*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements. See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License. You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
- package org.apache.commons.configuration2.builder;
- import java.util.Collection;
- import java.util.concurrent.CopyOnWriteArrayList;
- /**
- * <p>
- * A class for managing a set of {@link DefaultParametersHandler} objects.
- * </p>
- * <p>
- * This class provides functionality for registering and removing {@code DefaultParametersHandler} objects for arbitrary
- * parameters classes. The handlers registered at an instance can then be applied on a passed in parameters object, so
- * that it gets initialized with the provided default values.
- * </p>
- * <p>
- * Usage of this class is as follows: First the {@code DefaultParametersHandler} objects to be supported must be
- * registered using one of the {@code registerDefaultHandler()} methods. After that arbitrary parameters objects can be
- * passed to the {@code initializeParameters()} method. This causes all {@code DefaultParametersHandler} objects
- * supporting this parameters class to be invoked on this object.
- * </p>
- * <p>
- * Implementation note: This class is thread-safe.
- * </p>
- *
- * @since 2.0
- */
- public class DefaultParametersManager {
- /**
- * A data class storing information about {@code DefaultParametersHandler} objects added to a {@code Parameters} object.
- * Using this class it is possible to find out which default handlers apply for a given parameters object and to invoke
- * them.
- */
- private static final class DefaultHandlerData {
- /** The handler object. */
- private final DefaultParametersHandler<?> handler;
- /** The class supported by this handler. */
- private final Class<?> parameterClass;
- /** The start class for applying this handler. */
- private final Class<?> startClass;
- /**
- * Creates a new instance of {@code DefaultHandlerData}.
- *
- * @param h the {@code DefaultParametersHandler}
- * @param cls the handler's data class
- * @param startCls the start class
- */
- public DefaultHandlerData(final DefaultParametersHandler<?> h, final Class<?> cls, final Class<?> startCls) {
- handler = h;
- parameterClass = cls;
- startClass = startCls;
- }
- /**
- * Checks whether the managed {@code DefaultParametersHandler} can be applied to the given parameters object. If this is
- * the case, it is executed on this object and can initialize it with default values.
- *
- * @param obj the parameters object to be initialized
- */
- @SuppressWarnings("unchecked")
- // There are explicit isInstance() checks, so there won't be
- // ClassCastExceptions
- public void applyHandlerIfMatching(final BuilderParameters obj) {
- if (parameterClass.isInstance(obj) && (startClass == null || startClass.isInstance(obj))) {
- @SuppressWarnings("rawtypes")
- final DefaultParametersHandler handlerUntyped = handler;
- handlerUntyped.initializeDefaults(obj);
- }
- }
- /**
- * Tests whether this instance refers to the specified occurrence of a {@code DefaultParametersHandler}.
- *
- * @param h the handler to be checked
- * @param startCls the start class
- * @return <strong>true</strong> if this instance refers to this occurrence, <strong>false</strong> otherwise
- */
- public boolean isOccurrence(final DefaultParametersHandler<?> h, final Class<?> startCls) {
- return h == handler && (startCls == null || startCls.equals(startClass));
- }
- }
- /** A collection with the registered default handlers. */
- private final Collection<DefaultHandlerData> defaultHandlers;
- /**
- * Creates a new instance of {@code DefaultParametersManager}.
- */
- public DefaultParametersManager() {
- defaultHandlers = new CopyOnWriteArrayList<>();
- }
- /**
- * Initializes the passed in {@code BuilderParameters} object by applying all matching {@link DefaultParametersHandler}
- * objects registered at this instance. Using this method the passed in parameters object can be populated with default
- * values.
- *
- * @param params the parameters object to be initialized (may be <strong>null</strong>, then this method has no effect)
- */
- public void initializeParameters(final BuilderParameters params) {
- if (params != null) {
- defaultHandlers.forEach(dhd -> dhd.applyHandlerIfMatching(params));
- }
- }
- /**
- * Registers the specified {@code DefaultParametersHandler} object for the given parameters class. This means that this
- * handler object is invoked every time a parameters object of the specified class or one of its subclasses is
- * initialized. The handler can set arbitrary default values for the properties supported by this parameters object. If
- * there are multiple handlers registered supporting a specific parameters class, they are invoked in the order in which
- * they were registered. So handlers registered later may override the values set by handlers registered earlier.
- *
- * @param <T> the type of the parameters supported by this handler
- * @param paramsClass the parameters class supported by this handler (must not be <strong>null</strong>)
- * @param handler the {@code DefaultParametersHandler} to be registered (must not be <strong>null</strong>)
- * @throws IllegalArgumentException if a required parameter is missing
- */
- public <T> void registerDefaultsHandler(final Class<T> paramsClass, final DefaultParametersHandler<? super T> handler) {
- registerDefaultsHandler(paramsClass, handler, null);
- }
- /**
- * Registers the specified {@code DefaultParametersHandler} object for the given parameters class and start class in the
- * inheritance hierarchy. This method works like {@link #registerDefaultsHandler(Class, DefaultParametersHandler)}, but
- * the defaults handler is only executed on parameter objects that are instances of the specified start class. Parameter
- * classes do not stand in a real inheritance hierarchy; however, there is a logic hierarchy defined by the methods
- * supported by the different parameter objects. A properties parameter object for instance supports all methods defined
- * for a file-based parameter object. So one can argue that
- * {@link org.apache.commons.configuration2.builder.fluent.FileBasedBuilderParameters FileBasedBuilderParameters} is a
- * base interface of {@link org.apache.commons.configuration2.builder.fluent.PropertiesBuilderParameters
- * PropertiesBuilderParameters} (although, for technical reasons, this relation is not reflected in the Java classes). A
- * {@link DefaultParametersHandler} object defined for a base interface can also deal with parameter objects "derived"
- * from this base interface (i.e. supporting a super set of the methods defined by the base interface). Now there may be
- * the use case that there is an implementation of {@code DefaultParametersHandler} for a base interface (for example
- * {@code FileBasedBuilderParameters}), but it should only process specific derived interfaces (say
- * {@code PropertiesBuilderParameters}, but not
- * {@link org.apache.commons.configuration2.builder.fluent.XMLBuilderParameters XMLBuilderParameters}). This can be
- * achieved by passing in {@code PropertiesBuilderParameters} as start class. In this case,
- * {@code DefaultParametersManager} ensures that the handler is only called on parameter objects having both the start
- * class and the actual type supported by the handler as base interfaces. The passed in start class can be <strong>null</strong>;
- * then the parameter class supported by the handler is used (which is the default behavior of the
- * {@link #registerDefaultsHandler(Class, DefaultParametersHandler)} method).
- *
- * @param <T> the type of the parameters supported by this handler
- * @param paramsClass the parameters class supported by this handler (must not be <strong>null</strong>)
- * @param handler the {@code DefaultParametersHandler} to be registered (must not be <strong>null</strong>)
- * @param startClass an optional start class in the hierarchy of parameter objects for which this handler should be
- * applied
- * @throws IllegalArgumentException if a required parameter is missing
- */
- public <T> void registerDefaultsHandler(final Class<T> paramsClass, final DefaultParametersHandler<? super T> handler, final Class<?> startClass) {
- if (paramsClass == null) {
- throw new IllegalArgumentException("Parameters class must not be null!");
- }
- if (handler == null) {
- throw new IllegalArgumentException("DefaultParametersHandler must not be null!");
- }
- defaultHandlers.add(new DefaultHandlerData(handler, paramsClass, startClass));
- }
- /**
- * Removes the specified {@code DefaultParametersHandler} from this instance. If this handler has been registered
- * multiple times for different start classes, all occurrences are removed.
- *
- * @param handler the {@code DefaultParametersHandler} to be removed
- */
- public void unregisterDefaultsHandler(final DefaultParametersHandler<?> handler) {
- unregisterDefaultsHandler(handler, null);
- }
- /**
- * Removes the specified {@code DefaultParametersHandler} from this instance if it is in combination with the given
- * start class. If this handler has been registered multiple times for different start classes, only occurrences for the
- * given start class are removed. The {@code startClass} parameter can be <strong>null</strong>, then all occurrences of the
- * handler are removed.
- *
- * @param handler the {@code DefaultParametersHandler} to be removed
- * @param startClass the start class for which this handler is to be removed
- */
- public void unregisterDefaultsHandler(final DefaultParametersHandler<?> handler, final Class<?> startClass) {
- defaultHandlers.removeIf(dhd -> dhd.isOccurrence(handler, startClass));
- }
- }