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.Map; 20 21 import org.apache.commons.configuration2.FileBasedConfiguration; 22 import org.apache.commons.configuration2.ex.ConfigurationException; 23 import org.apache.commons.configuration2.io.FileHandler; 24 import org.apache.commons.configuration2.reloading.ReloadingController; 25 import org.apache.commons.configuration2.reloading.ReloadingControllerSupport; 26 import org.apache.commons.configuration2.reloading.ReloadingDetector; 27 28 /** 29 * <p> 30 * A specialized {@code ConfigurationBuilder} implementation which can handle configurations read from a 31 * {@link FileHandler} and supports reloading. 32 * </p> 33 * <p> 34 * This builder class exposes a {@link ReloadingController} object controlling reload operations on the file-based 35 * configuration produced as result object. For the {@code FileHandler} defining the location of the configuration a 36 * configurable {@link ReloadingDetector} is created and associated with the controller. So changes on the source file 37 * can be detected. When ever such a change occurs, the result object of this builder is reset. This means that the next 38 * time {@code getConfiguration()} is called a new {@code Configuration} object is created which is loaded from the 39 * modified file. 40 * </p> 41 * <p> 42 * Client code interested in notifications can register a listener at this builder to receive reset events. When such an 43 * event is received the new result object can be requested. This way client applications can be sure to work with an 44 * up-to-date configuration. It is also possible to register a listener directly at the {@code ReloadingController}. 45 * </p> 46 * <p> 47 * This builder does not actively trigger the {@code ReloadingController} to perform a reload check. This has to be done 48 * by an external component, e.g. a timer. 49 * </p> 50 * 51 * @since 2.0 52 * @param <T> the concrete type of {@code Configuration} objects created by this builder 53 */ 54 public class ReloadingFileBasedConfigurationBuilder<T extends FileBasedConfiguration> extends FileBasedConfigurationBuilder<T> 55 implements ReloadingControllerSupport { 56 /** The default factory for creating reloading detector objects. */ 57 private static final ReloadingDetectorFactory DEFAULT_DETECTOR_FACTORY = new DefaultReloadingDetectorFactory(); 58 59 /** The reloading controller associated with this object. */ 60 private final ReloadingController reloadingController; 61 62 /** 63 * The reloading detector which does the actual reload check for the current result object. A new instance is created 64 * whenever a new result object (and thus a new current file handler) becomes available. The field must be volatile 65 * because it is accessed by the reloading controller probably from within another thread. 66 */ 67 private volatile ReloadingDetector resultReloadingDetector; 68 69 /** 70 * Creates a new instance of {@code ReloadingFileBasedConfigurationBuilder} which produces result objects of the 71 * specified class and sets initialization parameters. 72 * 73 * @param resCls the result class (must not be <b>null</b> 74 * @param params a map with initialization parameters 75 * @throws IllegalArgumentException if the result class is <b>null</b> 76 */ 77 public ReloadingFileBasedConfigurationBuilder(final Class<? extends T> resCls, final Map<String, Object> params) { 78 super(resCls, params); 79 reloadingController = createReloadingController(); 80 } 81 82 /** 83 * Creates a new instance of {@code ReloadingFileBasedConfigurationBuilder} which produces result objects of the 84 * specified class and sets initialization parameters and the <em>allowFailOnInit</em> flag. 85 * 86 * @param resCls the result class (must not be <b>null</b> 87 * @param params a map with initialization parameters 88 * @param allowFailOnInit the <em>allowFailOnInit</em> flag 89 * @throws IllegalArgumentException if the result class is <b>null</b> 90 */ 91 public ReloadingFileBasedConfigurationBuilder(final Class<? extends T> resCls, final Map<String, Object> params, final boolean allowFailOnInit) { 92 super(resCls, params, allowFailOnInit); 93 reloadingController = createReloadingController(); 94 } 95 96 /** 97 * Creates a new instance of {@code ReloadingFileBasedConfigurationBuilder} which produces result objects of the 98 * specified class. 99 * 100 * @param resCls the result class (must not be <b>null</b> 101 * @throws IllegalArgumentException if the result class is <b>null</b> 102 */ 103 public ReloadingFileBasedConfigurationBuilder(final Class<? extends T> resCls) { 104 super(resCls); 105 reloadingController = createReloadingController(); 106 } 107 108 /** 109 * Gets the {@code ReloadingController} associated with this builder. This controller is directly created. However, 110 * it becomes active (i.e. associated with a meaningful reloading detector) not before a result object was created. 111 * 112 * @return the {@code ReloadingController} 113 */ 114 @Override 115 public ReloadingController getReloadingController() { 116 return reloadingController; 117 } 118 119 /** 120 * {@inheritDoc} This method is overridden here to change the result type. 121 */ 122 @Override 123 public ReloadingFileBasedConfigurationBuilder<T> configure(final BuilderParameters... params) { 124 super.configure(params); 125 return this; 126 } 127 128 /** 129 * Creates a {@code ReloadingDetector} which monitors the passed in {@code FileHandler}. This method is called each time 130 * a new result object is created with the current {@code FileHandler}. This implementation checks whether a 131 * {@code ReloadingDetectorFactory} is specified in the current parameters. If this is the case, it is invoked. 132 * Otherwise, a default factory is used to create a {@code FileHandlerReloadingDetector} object. Note: This method is 133 * called from a synchronized block. 134 * 135 * @param handler the current {@code FileHandler} 136 * @param fbparams the object with parameters related to file-based builders 137 * @return a {@code ReloadingDetector} for this {@code FileHandler} 138 * @throws ConfigurationException if an error occurs 139 */ 140 protected ReloadingDetector createReloadingDetector(final FileHandler handler, final FileBasedBuilderParametersImpl fbparams) 141 throws ConfigurationException { 142 return fetchDetectorFactory(fbparams).createReloadingDetector(handler, fbparams); 143 } 144 145 /** 146 * {@inheritDoc} This implementation also takes care that a new {@code ReloadingDetector} for the new current 147 * {@code FileHandler} is created. Also, the reloading controller's reloading state has to be reset; after the creation 148 * of a new result object changes in the underlying configuration source have to be monitored again. 149 */ 150 @Override 151 protected void initFileHandler(final FileHandler handler) throws ConfigurationException { 152 super.initFileHandler(handler); 153 154 resultReloadingDetector = createReloadingDetector(handler, FileBasedBuilderParametersImpl.fromParameters(getParameters(), true)); 155 } 156 157 /** 158 * Creates the {@code ReloadingController} associated with this object. The controller is assigned a specialized 159 * reloading detector which delegates to the detector for the current result object. ( 160 * {@code FileHandlerReloadingDetector} does not support changing the file handler, and {@code ReloadingController} does 161 * not support changing the reloading detector; therefore, this level of indirection is needed to change the monitored 162 * file dynamically.) 163 * 164 * @return the new {@code ReloadingController} 165 */ 166 private ReloadingController createReloadingController() { 167 final ReloadingDetector ctrlDetector = createReloadingDetectorForController(); 168 final ReloadingController ctrl = new ReloadingController(ctrlDetector); 169 connectToReloadingController(ctrl); 170 return ctrl; 171 } 172 173 /** 174 * Creates a {@code ReloadingDetector} wrapper to be passed to the associated {@code ReloadingController}. This detector 175 * wrapper simply delegates to the current {@code ReloadingDetector} if it is available. 176 * 177 * @return the wrapper {@code ReloadingDetector} 178 */ 179 private ReloadingDetector createReloadingDetectorForController() { 180 return new ReloadingDetector() { 181 @Override 182 public void reloadingPerformed() { 183 final ReloadingDetector detector = resultReloadingDetector; 184 if (detector != null) { 185 detector.reloadingPerformed(); 186 } 187 } 188 189 @Override 190 public boolean isReloadingRequired() { 191 final ReloadingDetector detector = resultReloadingDetector; 192 return detector != null && detector.isReloadingRequired(); 193 } 194 }; 195 } 196 197 /** 198 * Returns a {@code ReloadingDetectorFactory} either from the passed in parameters or a default factory. 199 * 200 * @param params the current parameters object 201 * @return the {@code ReloadingDetectorFactory} to be used 202 */ 203 private static ReloadingDetectorFactory fetchDetectorFactory(final FileBasedBuilderParametersImpl params) { 204 final ReloadingDetectorFactory factory = params.getReloadingDetectorFactory(); 205 return factory != null ? factory : DEFAULT_DETECTOR_FACTORY; 206 } 207 }