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.configuration2.builder; 18 19 import java.util.Collection; 20 import java.util.concurrent.CopyOnWriteArrayList; 21 22 /** 23 * <p> 24 * A class for managing a set of {@link DefaultParametersHandler} objects. 25 * </p> 26 * <p> 27 * This class provides functionality for registering and removing {@code DefaultParametersHandler} objects for arbitrary 28 * parameters classes. The handlers registered at an instance can then be applied on a passed in parameters object, so 29 * that it gets initialized with the provided default values. 30 * </p> 31 * <p> 32 * Usage of this class is as follows: First the {@code DefaultParametersHandler} objects to be supported must be 33 * registered using one of the {@code registerDefaultHandler()} methods. After that arbitrary parameters objects can be 34 * passed to the {@code initializeParameters()} method. This causes all {@code DefaultParametersHandler} objects 35 * supporting this parameters class to be invoked on this object. 36 * </p> 37 * <p> 38 * Implementation note: This class is thread-safe. 39 * </p> 40 * 41 * @since 2.0 42 */ 43 public class DefaultParametersManager { 44 /** A collection with the registered default handlers. */ 45 private final Collection<DefaultHandlerData> defaultHandlers; 46 47 /** 48 * Creates a new instance of {@code DefaultParametersManager}. 49 */ 50 public DefaultParametersManager() { 51 defaultHandlers = new CopyOnWriteArrayList<>(); 52 } 53 54 /** 55 * Registers the specified {@code DefaultParametersHandler} object for the given parameters class. This means that this 56 * handler object is invoked every time a parameters object of the specified class or one of its subclasses is 57 * initialized. The handler can set arbitrary default values for the properties supported by this parameters object. If 58 * there are multiple handlers registered supporting a specific parameters class, they are invoked in the order in which 59 * they were registered. So handlers registered later may override the values set by handlers registered earlier. 60 * 61 * @param <T> the type of the parameters supported by this handler 62 * @param paramsClass the parameters class supported by this handler (must not be <b>null</b>) 63 * @param handler the {@code DefaultParametersHandler} to be registered (must not be <b>null</b>) 64 * @throws IllegalArgumentException if a required parameter is missing 65 */ 66 public <T> void registerDefaultsHandler(final Class<T> paramsClass, final DefaultParametersHandler<? super T> handler) { 67 registerDefaultsHandler(paramsClass, handler, null); 68 } 69 70 /** 71 * Registers the specified {@code DefaultParametersHandler} object for the given parameters class and start class in the 72 * inheritance hierarchy. This method works like {@link #registerDefaultsHandler(Class, DefaultParametersHandler)}, but 73 * the defaults handler is only executed on parameter objects that are instances of the specified start class. Parameter 74 * classes do not stand in a real inheritance hierarchy; however, there is a logic hierarchy defined by the methods 75 * supported by the different parameter objects. A properties parameter object for instance supports all methods defined 76 * for a file-based parameter object. So one can argue that 77 * {@link org.apache.commons.configuration2.builder.fluent.FileBasedBuilderParameters FileBasedBuilderParameters} is a 78 * base interface of {@link org.apache.commons.configuration2.builder.fluent.PropertiesBuilderParameters 79 * PropertiesBuilderParameters} (although, for technical reasons, this relation is not reflected in the Java classes). A 80 * {@link DefaultParametersHandler} object defined for a base interface can also deal with parameter objects "derived" 81 * from this base interface (i.e. supporting a super set of the methods defined by the base interface). Now there may be 82 * the use case that there is an implementation of {@code DefaultParametersHandler} for a base interface (e.g. 83 * {@code FileBasedBuilderParameters}), but it should only process specific derived interfaces (say 84 * {@code PropertiesBuilderParameters}, but not 85 * {@link org.apache.commons.configuration2.builder.fluent.XMLBuilderParameters XMLBuilderParameters}). This can be 86 * achieved by passing in {@code PropertiesBuilderParameters} as start class. In this case, 87 * {@code DefaultParametersManager} ensures that the handler is only called on parameter objects having both the start 88 * class and the actual type supported by the handler as base interfaces. The passed in start class can be <b>null</b>; 89 * then the parameter class supported by the handler is used (which is the default behavior of the 90 * {@link #registerDefaultsHandler(Class, DefaultParametersHandler)} method). 91 * 92 * @param <T> the type of the parameters supported by this handler 93 * @param paramsClass the parameters class supported by this handler (must not be <b>null</b>) 94 * @param handler the {@code DefaultParametersHandler} to be registered (must not be <b>null</b>) 95 * @param startClass an optional start class in the hierarchy of parameter objects for which this handler should be 96 * applied 97 * @throws IllegalArgumentException if a required parameter is missing 98 */ 99 public <T> void registerDefaultsHandler(final Class<T> paramsClass, final DefaultParametersHandler<? super T> handler, final Class<?> startClass) { 100 if (paramsClass == null) { 101 throw new IllegalArgumentException("Parameters class must not be null!"); 102 } 103 if (handler == null) { 104 throw new IllegalArgumentException("DefaultParametersHandler must not be null!"); 105 } 106 defaultHandlers.add(new DefaultHandlerData(handler, paramsClass, startClass)); 107 } 108 109 /** 110 * Removes the specified {@code DefaultParametersHandler} from this instance. If this handler has been registered 111 * multiple times for different start classes, all occurrences are removed. 112 * 113 * @param handler the {@code DefaultParametersHandler} to be removed 114 */ 115 public void unregisterDefaultsHandler(final DefaultParametersHandler<?> handler) { 116 unregisterDefaultsHandler(handler, null); 117 } 118 119 /** 120 * Removes the specified {@code DefaultParametersHandler} from this instance if it is in combination with the given 121 * start class. If this handler has been registered multiple times for different start classes, only occurrences for the 122 * given start class are removed. The {@code startClass} parameter can be <b>null</b>, then all occurrences of the 123 * handler are removed. 124 * 125 * @param handler the {@code DefaultParametersHandler} to be removed 126 * @param startClass the start class for which this handler is to be removed 127 */ 128 public void unregisterDefaultsHandler(final DefaultParametersHandler<?> handler, final Class<?> startClass) { 129 defaultHandlers.removeIf(dhd -> dhd.isOccurrence(handler, startClass)); 130 } 131 132 /** 133 * Initializes the passed in {@code BuilderParameters} object by applying all matching {@link DefaultParametersHandler} 134 * objects registered at this instance. Using this method the passed in parameters object can be populated with default 135 * values. 136 * 137 * @param params the parameters object to be initialized (may be <b>null</b>, then this method has no effect) 138 */ 139 public void initializeParameters(final BuilderParameters params) { 140 if (params != null) { 141 defaultHandlers.forEach(dhd -> dhd.applyHandlerIfMatching(params)); 142 } 143 } 144 145 /** 146 * A data class storing information about {@code DefaultParametersHandler} objects added to a {@code Parameters} object. 147 * Using this class it is possible to find out which default handlers apply for a given parameters object and to invoke 148 * them. 149 */ 150 private static final class DefaultHandlerData { 151 /** The handler object. */ 152 private final DefaultParametersHandler<?> handler; 153 154 /** The class supported by this handler. */ 155 private final Class<?> parameterClass; 156 157 /** The start class for applying this handler. */ 158 private final Class<?> startClass; 159 160 /** 161 * Creates a new instance of {@code DefaultHandlerData}. 162 * 163 * @param h the {@code DefaultParametersHandler} 164 * @param cls the handler's data class 165 * @param startCls the start class 166 */ 167 public DefaultHandlerData(final DefaultParametersHandler<?> h, final Class<?> cls, final Class<?> startCls) { 168 handler = h; 169 parameterClass = cls; 170 startClass = startCls; 171 } 172 173 /** 174 * Checks whether the managed {@code DefaultParametersHandler} can be applied to the given parameters object. If this is 175 * the case, it is executed on this object and can initialize it with default values. 176 * 177 * @param obj the parameters object to be initialized 178 */ 179 @SuppressWarnings("unchecked") 180 // There are explicit isInstance() checks, so there won't be 181 // ClassCastExceptions 182 public void applyHandlerIfMatching(final BuilderParameters obj) { 183 if (parameterClass.isInstance(obj) && (startClass == null || startClass.isInstance(obj))) { 184 @SuppressWarnings("rawtypes") 185 final DefaultParametersHandler handlerUntyped = handler; 186 handlerUntyped.initializeDefaults(obj); 187 } 188 } 189 190 /** 191 * Tests whether this instance refers to the specified occurrence of a {@code DefaultParametersHandler}. 192 * 193 * @param h the handler to be checked 194 * @param startCls the start class 195 * @return <b>true</b> if this instance refers to this occurrence, <b>false</b> otherwise 196 */ 197 public boolean isOccurrence(final DefaultParametersHandler<?> h, final Class<?> startCls) { 198 return h == handler && (startCls == null || startCls.equals(startClass)); 199 } 200 } 201 }