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.chain; 018 019import java.util.Iterator; 020import java.util.concurrent.ConcurrentHashMap; 021 022import org.apache.commons.chain.impl.CatalogFactoryBase; 023import org.slf4j.Logger; 024import org.slf4j.LoggerFactory; 025 026/** 027 * A {@link CatalogFactory} is a class used to store and retrieve 028 * {@link Catalog}s. The factory allows for a default {@link Catalog} 029 * as well as {@link Catalog}s stored with a name key. Follows the 030 * Factory pattern (see GoF). 031 * 032 * <p>The base {@code CatalogFactory} implementation also implements 033 * a resolution mechanism which allows lookup of a command based on a single 034 * String which encodes both the catalog and command names.</p> 035 * 036 * @param <C> Type of the context associated with this command 037 * 038 * @author Sean Schofield 039 * @version $Revision$ $Date$ 040 */ 041public abstract class CatalogFactory<C extends Context> { 042 043 // ------------------------------------------------------- Static Variables 044 045 /** 046 * Values passed to the {@code getCommand(String)} method should 047 * use this as the delimiter between the "catalog" name and the "command" 048 * name. 049 */ 050 public static final String DELIMITER = ":"; 051 052 /** 053 * The set of registered {@link CatalogFactory} instances, 054 * keyed by the relevant class loader. 055 */ 056 private static final ConcurrentHashMap<ClassLoader, CatalogFactory<?>> FACTORIES = new ConcurrentHashMap<>(); 057 058 // --------------------------------------------------------- Public Methods 059 060 /** 061 * Gets the default instance of Catalog associated with the factory 062 * (if any); otherwise, return {@code null}. 063 * 064 * @return the default Catalog instance 065 */ 066 public abstract Catalog<C> getCatalog(); 067 068 /** 069 * Sets the default instance of Catalog associated with the factory. 070 * 071 * @param catalog the default Catalog instance 072 */ 073 public abstract void setCatalog(Catalog<C> catalog); 074 075 /** 076 * Retrieves a Catalog instance by name (if any); otherwise 077 * return {@code null}. 078 * 079 * @param name the name of the Catalog to retrieve 080 * 081 * @return the specified Catalog 082 */ 083 public abstract Catalog<C> getCatalog(String name); 084 085 /** 086 * Adds a named instance of Catalog to the factory (for subsequent 087 * retrieval later). 088 * 089 * @param name the name of the Catalog to add 090 * @param catalog the Catalog to add 091 */ 092 public abstract void addCatalog(String name, Catalog<C> catalog); 093 094 /** 095 * Return an {@code Iterator} over the set of named 096 * {@link Catalog}s known to this {@link CatalogFactory}. 097 * If there are no known catalogs, an empty Iterator is returned. 098 * 099 * @return An Iterator of the names of the Catalogs known by this factory. 100 */ 101 public abstract Iterator<String> getNames(); 102 103 /** 104 * The Default-Constructor for this class. 105 */ 106 public CatalogFactory() { 107 } 108 109 /** 110 * Return a {@code Command} based on the given commandID. 111 * 112 * <p>At this time, the structure of commandID is relatively simple: if the 113 * commandID contains a DELIMITER, treat the segment of the commandID 114 * up to (but not including) the DELIMITER as the name of a catalog, and the 115 * segment following the DELIMITER as a command name within that catalog. 116 * If the commandID contains no DELIMITER, treat the commandID as the name 117 * of a command in the default catalog.</p> 118 * 119 * <p>To preserve the possibility of future extensions to this lookup 120 * mechanism, the DELIMITER string should be considered reserved, and 121 * should not be used in command names. commandID values which contain 122 * more than one DELIMITER will cause an {@code IllegalArgumentException} 123 * to be thrown.</p> 124 * 125 * @param <CMD> the expected {@link Command} type to be returned 126 * @param commandID the identifier of the command to return 127 * 128 * @return the command located with commandID, or {@code null} 129 * if either the command name or the catalog name cannot be 130 * resolved 131 * 132 * @throws IllegalArgumentException if the commandID contains more than 133 * one DELIMITER 134 * 135 * @since Chain 1.1 136 */ 137 public <CMD extends Command<C>> CMD getCommand(String commandID) { 138 String commandName = commandID; 139 String catalogName = null; 140 Catalog<C> catalog = null; 141 142 if (commandID != null) { 143 int splitPos = commandID.indexOf(DELIMITER); 144 if (splitPos != -1) { 145 catalogName = commandID.substring(0, splitPos); 146 commandName = commandID.substring(splitPos + DELIMITER.length()); 147 if (commandName.contains(DELIMITER)) { 148 throw new IllegalArgumentException("commandID [" 149 + commandID + "] has too many delimiters (reserved for future use)"); 150 } 151 } 152 } 153 154 if (catalogName != null) { 155 catalog = this.getCatalog(catalogName); 156 if (catalog == null) { 157 Logger logger = LoggerFactory.getLogger(CatalogFactory.class); 158 logger.warn("No catalog found for name: {}.", catalogName); 159 return null; 160 } 161 } else { 162 catalog = this.getCatalog(); 163 if (catalog == null) { 164 Logger logger = LoggerFactory.getLogger(CatalogFactory.class); 165 logger.warn("No default catalog found."); 166 return null; 167 } 168 } 169 170 return catalog.getCommand(commandName); 171 } 172 173 // -------------------------------------------------------- Static Methods 174 175 /** 176 * Return the singleton {@link CatalogFactory} instance 177 * for the relevant {@code ClassLoader}. For applications 178 * that use a thread context class loader (such as web applications 179 * running inside a servet container), this will return a separate 180 * instance for each application, even if this class is loaded from 181 * a shared parent class loader. 182 * 183 * @param <C> Type of the context associated with this command 184 * 185 * @return the per-application singleton instance of {@link CatalogFactory} 186 */ 187 public static <C extends Context> CatalogFactory<C> getInstance() { 188 ClassLoader cl = getClassLoader(); 189 190 @SuppressWarnings("unchecked") 191 CatalogFactory<C> ret = (CatalogFactory<C>) FACTORIES.computeIfAbsent(cl, k -> new CatalogFactoryBase<>()); 192 return ret; 193 } 194 195 /** 196 * Clear all references to registered catalogs, as well as to the 197 * relevant class loader. This method should be called, for example, 198 * when a web application utilizing this class is removed from 199 * service, to allow for garbage collection. 200 */ 201 public static void clear() { 202 FACTORIES.remove(getClassLoader()); 203 } 204 205 // ------------------------------------------------------- Private Methods 206 207 /** 208 * Return the relevant {@code ClassLoader} to use as a Map key 209 * for this request. If there is a thread context class loader, return 210 * that; otherwise, return the class loader that loaded this class. 211 * 212 * @return the relevant {@code ClassLoader} to use as a Map key for this request 213 */ 214 private static ClassLoader getClassLoader() { 215 ClassLoader cl = Thread.currentThread().getContextClassLoader(); 216 if (cl == null) { 217 cl = CatalogFactory.class.getClassLoader(); 218 } 219 return cl; 220 } 221}