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.LinkedList; 021import java.util.concurrent.CopyOnWriteArrayList; 022 023/** 024 * <p> 025 * A class for managing a set of {@link DefaultParametersHandler} objects. 026 * </p> 027 * <p> 028 * This class provides functionality for registering and removing 029 * {@code DefaultParametersHandler} objects for arbitrary parameters classes. 030 * The handlers registered at an instance can then be applied on a passed in 031 * parameters object, so that it gets initialized with the provided default 032 * values. 033 * </p> 034 * <p> 035 * Usage of this class is as follows: First the {@code DefaultParametersHandler} 036 * objects to be supported must be registered using one of the 037 * {@code registerDefaultHandler()} methods. After that arbitrary parameters 038 * objects can be passed to the {@code initializeParameters()} method. This 039 * causes all {@code DefaultParametersHandler} objects supporting this 040 * parameters class to be invoked on this object. 041 * </p> 042 * <p> 043 * Implementation note: This class is thread-safe. 044 * </p> 045 * 046 * @since 2.0 047 */ 048public class DefaultParametersManager 049{ 050 /** A collection with the registered default handlers. */ 051 private final Collection<DefaultHandlerData> defaultHandlers; 052 053 /** 054 * Creates a new instance of {@code DefaultParametersManager}. 055 */ 056 public DefaultParametersManager() 057 { 058 defaultHandlers = new CopyOnWriteArrayList<>(); 059 } 060 061 /** 062 * Registers the specified {@code DefaultParametersHandler} object for the 063 * given parameters class. This means that this handler object is invoked 064 * every time a parameters object of the specified class or one of its 065 * subclasses is initialized. The handler can set arbitrary default values 066 * for the properties supported by this parameters object. If there are 067 * multiple handlers registered supporting a specific parameters class, they 068 * are invoked in the order in which they were registered. So handlers 069 * registered later may override the values set by handlers registered 070 * earlier. 071 * 072 * @param <T> the type of the parameters supported by this handler 073 * @param paramsClass the parameters class supported by this handler (must 074 * not be <b>null</b>) 075 * @param handler the {@code DefaultParametersHandler} to be registered 076 * (must not be <b>null</b>) 077 * @throws IllegalArgumentException if a required parameter is missing 078 */ 079 public <T> void registerDefaultsHandler(final Class<T> paramsClass, 080 final DefaultParametersHandler<? super T> handler) 081 { 082 registerDefaultsHandler(paramsClass, handler, null); 083 } 084 085 /** 086 * Registers the specified {@code DefaultParametersHandler} object for the 087 * given parameters class and start class in the inheritance hierarchy. This 088 * method works like 089 * {@link #registerDefaultsHandler(Class, DefaultParametersHandler)}, but 090 * the defaults handler is only executed on parameter objects that are 091 * instances of the specified start class. Parameter classes do not stand in 092 * a real inheritance hierarchy; however, there is a logic hierarchy defined 093 * by the methods supported by the different parameter objects. A properties 094 * parameter object for instance supports all methods defined for a 095 * file-based parameter object. So one can argue that 096 * {@link org.apache.commons.configuration2.builder.fluent.FileBasedBuilderParameters 097 * FileBasedBuilderParameters} is a base interface of 098 * {@link org.apache.commons.configuration2.builder.fluent.PropertiesBuilderParameters 099 * PropertiesBuilderParameters} (although, for technical reasons, 100 * this relation is not reflected in the Java classes). A 101 * {@link DefaultParametersHandler} object defined for a base interface can 102 * also deal with parameter objects "derived" from this base interface (i.e. 103 * supporting a super set of the methods defined by the base interface). Now 104 * there may be the use case that there is an implementation of 105 * {@code DefaultParametersHandler} for a base interface (e.g. 106 * {@code FileBasedBuilderParameters}), but it should only process specific 107 * derived interfaces (say {@code PropertiesBuilderParameters}, but not 108 * {@link org.apache.commons.configuration2.builder.fluent.XMLBuilderParameters 109 * XMLBuilderParameters}). This can be achieved by passing in 110 * {@code PropertiesBuilderParameters} as start class. In this case, 111 * {@code DefaultParametersManager} ensures that the handler is only called 112 * on parameter objects having both the start class and the actual type 113 * supported by the handler as base interfaces. The passed in start class 114 * can be <b>null</b>; then the parameter class supported by the handler is 115 * used (which is the default behavior of the 116 * {@link #registerDefaultsHandler(Class, DefaultParametersHandler)} 117 * method). 118 * 119 * @param <T> the type of the parameters supported by this handler 120 * @param paramsClass the parameters class supported by this handler (must 121 * not be <b>null</b>) 122 * @param handler the {@code DefaultParametersHandler} to be registered 123 * (must not be <b>null</b>) 124 * @param startClass an optional start class in the hierarchy of parameter 125 * objects for which this handler should be applied 126 * @throws IllegalArgumentException if a required parameter is missing 127 */ 128 public <T> void registerDefaultsHandler(final Class<T> paramsClass, 129 final DefaultParametersHandler<? super T> handler, final Class<?> startClass) 130 { 131 if (paramsClass == null) 132 { 133 throw new IllegalArgumentException( 134 "Parameters class must not be null!"); 135 } 136 if (handler == null) 137 { 138 throw new IllegalArgumentException( 139 "DefaultParametersHandler must not be null!"); 140 } 141 defaultHandlers.add(new DefaultHandlerData(handler, paramsClass, 142 startClass)); 143 } 144 145 /** 146 * Removes the specified {@code DefaultParametersHandler} from this 147 * instance. If this handler has been registered multiple times for 148 * different start classes, all occurrences are removed. 149 * 150 * @param handler the {@code DefaultParametersHandler} to be removed 151 */ 152 public void unregisterDefaultsHandler(final DefaultParametersHandler<?> handler) 153 { 154 unregisterDefaultsHandler(handler, null); 155 } 156 157 /** 158 * Removes the specified {@code DefaultParametersHandler} from this instance 159 * if it is in combination with the given start class. If this handler has 160 * been registered multiple times for different start classes, only 161 * occurrences for the given start class are removed. The {@code startClass} 162 * parameter can be <b>null</b>, then all occurrences of the handler are 163 * removed. 164 * 165 * @param handler the {@code DefaultParametersHandler} to be removed 166 * @param startClass the start class for which this handler is to be removed 167 */ 168 public void unregisterDefaultsHandler(final DefaultParametersHandler<?> handler, 169 final Class<?> startClass) 170 { 171 final Collection<DefaultHandlerData> toRemove = 172 new LinkedList<>(); 173 for (final DefaultHandlerData dhd : defaultHandlers) 174 { 175 if (dhd.isOccurrence(handler, startClass)) 176 { 177 toRemove.add(dhd); 178 } 179 } 180 181 defaultHandlers.removeAll(toRemove); 182 } 183 184 /** 185 * Initializes the passed in {@code BuilderParameters} object by applying 186 * all matching {@link DefaultParametersHandler} objects registered at this 187 * instance. Using this method the passed in parameters object can be 188 * populated with default values. 189 * 190 * @param params the parameters object to be initialized (may be 191 * <b>null</b>, then this method has no effect) 192 */ 193 public void initializeParameters(final BuilderParameters params) 194 { 195 if (params != null) 196 { 197 for (final DefaultHandlerData dhd : defaultHandlers) 198 { 199 dhd.applyHandlerIfMatching(params); 200 } 201 } 202 } 203 204 /** 205 * A data class storing information about {@code DefaultParametersHandler} 206 * objects added to a {@code Parameters} object. Using this class it is 207 * possible to find out which default handlers apply for a given parameters 208 * object and to invoke them. 209 */ 210 private static class DefaultHandlerData 211 { 212 /** The handler object. */ 213 private final DefaultParametersHandler<?> handler; 214 215 /** The class supported by this handler. */ 216 private final Class<?> parameterClass; 217 218 /** The start class for applying this handler. */ 219 private final Class<?> startClass; 220 221 /** 222 * Creates a new instance of {@code DefaultHandlerData}. 223 * 224 * @param h the {@code DefaultParametersHandler} 225 * @param cls the handler's data class 226 * @param startCls the start class 227 */ 228 public DefaultHandlerData(final DefaultParametersHandler<?> h, final Class<?> cls, 229 final Class<?> startCls) 230 { 231 handler = h; 232 parameterClass = cls; 233 startClass = startCls; 234 } 235 236 /** 237 * Checks whether the managed {@code DefaultParametersHandler} can be 238 * applied to the given parameters object. If this is the case, it is 239 * executed on this object and can initialize it with default values. 240 * 241 * @param obj the parameters object to be initialized 242 */ 243 @SuppressWarnings("unchecked") 244 // There are explicit isInstance() checks, so there won't be 245 // ClassCastExceptions 246 public void applyHandlerIfMatching(final BuilderParameters obj) 247 { 248 if (parameterClass.isInstance(obj) 249 && (startClass == null || startClass.isInstance(obj))) 250 { 251 @SuppressWarnings("rawtypes") 252 final 253 DefaultParametersHandler handlerUntyped = handler; 254 handlerUntyped.initializeDefaults(obj); 255 } 256 } 257 258 /** 259 * Tests whether this instance refers to the specified occurrence of a 260 * {@code DefaultParametersHandler}. 261 * 262 * @param h the handler to be checked 263 * @param startCls the start class 264 * @return <b>true</b> if this instance refers to this occurrence, 265 * <b>false</b> otherwise 266 */ 267 public boolean isOccurrence(final DefaultParametersHandler<?> h, 268 final Class<?> startCls) 269 { 270 return h == handler 271 && (startCls == null || startCls.equals(startClass)); 272 } 273 } 274}