| 1 | package org.apache.velocity.context; |
| 2 | |
| 3 | /* |
| 4 | * Copyright 2001,2004 The Apache Software Foundation. |
| 5 | * |
| 6 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 7 | * you may not use this file except in compliance with the License. |
| 8 | * You may obtain a copy of the License at |
| 9 | * |
| 10 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 11 | * |
| 12 | * Unless required by applicable law or agreed to in writing, software |
| 13 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 14 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 15 | * See the License for the specific language governing permissions and |
| 16 | * limitations under the License. |
| 17 | */ |
| 18 | |
| 19 | import java.io.Serializable; |
| 20 | |
| 21 | import org.apache.velocity.context.Context; |
| 22 | import org.apache.velocity.context.InternalContextBase; |
| 23 | |
| 24 | /** |
| 25 | * This class is the abstract base class for all conventional |
| 26 | * Velocity Context implementations. Simply extend this class |
| 27 | * and implement the abstract routines that access your preferred |
| 28 | * storage method. |
| 29 | * |
| 30 | * Takes care of context chaining. |
| 31 | * |
| 32 | * Also handles / enforces policy on null keys and values : |
| 33 | * |
| 34 | * <ul> |
| 35 | * <li> Null keys and values are accepted and basically dropped. |
| 36 | * <li> If you place an object into the context with a null key, it |
| 37 | * will be ignored and logged. |
| 38 | * <li> If you try to place a null into the context with any key, it |
| 39 | * will be dropped and logged. |
| 40 | * </ul> |
| 41 | * |
| 42 | * The default implementation of this for application use is |
| 43 | * org.apache.velocity.VelocityContext. |
| 44 | * |
| 45 | * All thanks to Fedor for the chaining idea. |
| 46 | * |
| 47 | * @author <a href="mailto:geirm@optonline.net">Geir Magnusson Jr.</a> |
| 48 | * @author <a href="mailto:fedor.karpelevitch@home.com">Fedor Karpelevitch</a> |
| 49 | * @author <a href="mailto:jvanzyl@apache.org">Jason van Zyl</a> |
| 50 | * @version $Id: AbstractContext.java,v 1.8.8.1 2004/03/03 23:22:54 geirm Exp $ |
| 51 | */ |
| 52 | |
| 53 | public abstract class AbstractContext extends InternalContextBase |
| 54 | implements Context, Serializable |
| 55 | { |
| 56 | /** |
| 57 | * the chained Context if any |
| 58 | */ |
| 59 | private Context innerContext = null; |
| 60 | |
| 61 | /** |
| 62 | * Implement to return a value from the context storage. |
| 63 | * <br><br> |
| 64 | * The implementation of this method is required for proper |
| 65 | * operation of a Context implementation in general |
| 66 | * Velocity use. |
| 67 | * |
| 68 | * @param key key whose associated value is to be returned |
| 69 | * @return object stored in the context |
| 70 | */ |
| 71 | public abstract Object internalGet( String key ); |
| 72 | |
| 73 | /** |
| 74 | * Implement to put a value into the context storage. |
| 75 | * <br><br> |
| 76 | * The implementation of this method is required for |
| 77 | * proper operation of a Context implementation in |
| 78 | * general Velocity use. |
| 79 | * |
| 80 | * @param key key with which to associate the value |
| 81 | * @param value value to be associated with the key |
| 82 | * @return previously stored value if exists, or null |
| 83 | */ |
| 84 | public abstract Object internalPut( String key, Object value ); |
| 85 | |
| 86 | /** |
| 87 | * Implement to determine if a key is in the storage. |
| 88 | * <br><br> |
| 89 | * Currently, this method is not used internally by |
| 90 | * the Velocity core. |
| 91 | * |
| 92 | * @param key key to test for existance |
| 93 | * @return true if found, false if not |
| 94 | */ |
| 95 | public abstract boolean internalContainsKey(Object key); |
| 96 | |
| 97 | /** |
| 98 | * Implement to return an object array of key |
| 99 | * strings from your storage. |
| 100 | * <br><br> |
| 101 | * Currently, this method is not used internally by |
| 102 | * the Velocity core. |
| 103 | * |
| 104 | * @return array of keys |
| 105 | */ |
| 106 | public abstract Object[] internalGetKeys(); |
| 107 | |
| 108 | /** |
| 109 | * I mplement to remove an item from your storage. |
| 110 | * <br><br> |
| 111 | * Currently, this method is not used internally by |
| 112 | * the Velocity core. |
| 113 | * |
| 114 | * @param key key to remove |
| 115 | * @return object removed if exists, else null |
| 116 | */ |
| 117 | public abstract Object internalRemove(Object key); |
| 118 | |
| 119 | /** |
| 120 | * default CTOR |
| 121 | */ |
| 122 | public AbstractContext() |
| 123 | { |
| 124 | } |
| 125 | |
| 126 | /** |
| 127 | * Chaining constructor accepts a Context argument. |
| 128 | * It will relay get() operations into this Context |
| 129 | * in the even the 'local' get() returns null. |
| 130 | * |
| 131 | * @param inner context to be chained |
| 132 | */ |
| 133 | public AbstractContext( Context inner ) |
| 134 | { |
| 135 | innerContext = inner; |
| 136 | |
| 137 | /* |
| 138 | * now, do a 'forward pull' of event cartridge so |
| 139 | * it's accessable, bringing to the top level. |
| 140 | */ |
| 141 | |
| 142 | if (innerContext instanceof InternalEventContext ) |
| 143 | { |
| 144 | attachEventCartridge( ( (InternalEventContext) innerContext).getEventCartridge() ); |
| 145 | } |
| 146 | } |
| 147 | |
| 148 | /** |
| 149 | * Adds a name/value pair to the context. |
| 150 | * |
| 151 | * @param key The name to key the provided value with. |
| 152 | * @param value The corresponding value. |
| 153 | * @return Object that was replaced in the the Context if |
| 154 | * applicable or null if not. |
| 155 | */ |
| 156 | public Object put(String key, Object value) |
| 157 | { |
| 158 | /* |
| 159 | * don't even continue if key or value is null |
| 160 | */ |
| 161 | |
| 162 | if (key == null) |
| 163 | { |
| 164 | return null; |
| 165 | } |
| 166 | else if (value == null) |
| 167 | { |
| 168 | return null; |
| 169 | } |
| 170 | |
| 171 | return internalPut(key, value); |
| 172 | } |
| 173 | |
| 174 | /** |
| 175 | * Gets the value corresponding to the provided key from the context. |
| 176 | * |
| 177 | * Supports the chaining context mechanism. If the 'local' context |
| 178 | * doesn't have the value, we try to get it from the chained context. |
| 179 | * |
| 180 | * @param key The name of the desired value. |
| 181 | * @return The value corresponding to the provided key or null if |
| 182 | * the key param is null. |
| 183 | */ |
| 184 | public Object get(String key) |
| 185 | { |
| 186 | /* |
| 187 | * punt if key is null |
| 188 | */ |
| 189 | |
| 190 | if (key == null) |
| 191 | { |
| 192 | return null; |
| 193 | } |
| 194 | |
| 195 | /* |
| 196 | * get the object for this key. If null, and we are chaining another Context |
| 197 | * call the get() on it. |
| 198 | */ |
| 199 | |
| 200 | Object o = internalGet( key ); |
| 201 | |
| 202 | if (o == null && innerContext != null) |
| 203 | { |
| 204 | o = innerContext.get( key ); |
| 205 | } |
| 206 | |
| 207 | return o; |
| 208 | } |
| 209 | |
| 210 | /** |
| 211 | * Indicates whether the specified key is in the context. Provided for |
| 212 | * debugging purposes. |
| 213 | * |
| 214 | * @param key The key to look for. |
| 215 | * @return true if the key is in the context, false if not. |
| 216 | */ |
| 217 | public boolean containsKey(Object key) |
| 218 | { |
| 219 | if (key == null) |
| 220 | { |
| 221 | return false; |
| 222 | } |
| 223 | |
| 224 | return internalContainsKey(key); |
| 225 | } |
| 226 | |
| 227 | /** |
| 228 | * Get all the keys for the values in the context |
| 229 | * @return Object[] of keys in the Context. Does not return |
| 230 | * keys in chained context. |
| 231 | */ |
| 232 | public Object[] getKeys() |
| 233 | { |
| 234 | return internalGetKeys(); |
| 235 | } |
| 236 | |
| 237 | /** |
| 238 | * Removes the value associated with the specified key from the context. |
| 239 | * |
| 240 | * @param key The name of the value to remove. |
| 241 | * @return The value that the key was mapped to, or <code>null</code> |
| 242 | * if unmapped. |
| 243 | */ |
| 244 | public Object remove(Object key) |
| 245 | { |
| 246 | if (key == null) |
| 247 | { |
| 248 | return null; |
| 249 | } |
| 250 | |
| 251 | return internalRemove(key); |
| 252 | } |
| 253 | |
| 254 | /** |
| 255 | * returns innerContext if one is chained |
| 256 | * |
| 257 | * @return Context if chained, <code>null</code> if not |
| 258 | */ |
| 259 | public Context getChainedContext() |
| 260 | { |
| 261 | return innerContext; |
| 262 | } |
| 263 | |
| 264 | } |
| 265 | |
| 266 | |
| 267 | |