Source Code Cross Referenced for CompositeELResolver.java in  » Scripting » JUEL » javax » el » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Scripting » JUEL » javax.el 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         * The contents of this file are subject to the terms
003:         * of the Common Development and Distribution License
004:         * (the "License").  You may not use this file except
005:         * in compliance with the License.
006:         *
007:         * You can obtain a copy of the license at
008:         * glassfish/bootstrap/legal/CDDLv1.0.txt or
009:         * https://glassfish.dev.java.net/public/CDDLv1.0.html.
010:         * See the License for the specific language governing
011:         * permissions and limitations under the License.
012:         *
013:         * When distributing Covered Code, include this CDDL
014:         * HEADER in each file and include the License file at
015:         * glassfish/bootstrap/legal/CDDLv1.0.txt.  If applicable,
016:         * add the following below this CDDL HEADER, with the
017:         * fields enclosed by brackets "[]" replaced with your
018:         * own identifying information: Portions Copyright [yyyy]
019:         * [name of copyright owner]
020:         *
021:         * Copyright 2005 Sun Microsystems, Inc. All rights reserved.
022:         */
023:
024:        package javax.el;
025:
026:        import java.util.ArrayList;
027:        import java.util.Iterator;
028:        import java.beans.FeatureDescriptor;
029:
030:        /**
031:         * Maintains an ordered composite list of child <code>ELResolver</code>s.
032:         *
033:         * <p>Though only a single <code>ELResolver</code> is associated with an
034:         * <code>ELContext</code>, there are usually multiple resolvers considered
035:         * for any given variable or property resolution. <code>ELResolver</code>s
036:         * are combined together using a <code>CompositeELResolver</code>, to define
037:         * rich semantics for evaluating an expression.</p>
038:         *
039:         * <p>For the {@link #getValue}, {@link #getType}, {@link #setValue} and
040:         * {@link #isReadOnly} methods, an <code>ELResolver</code> is not
041:         * responsible for resolving all possible (base, property) pairs. In fact,
042:         * most resolvers will only handle a <code>base</code> of a single type.
043:         * To indicate that a resolver has successfully resolved a particular
044:         * (base, property) pair, it must set the <code>propertyResolved</code>
045:         * property of the <code>ELContext</code> to <code>true</code>. If it could 
046:         * not handle the given pair, it must leave this property alone. The caller
047:         * must ignore the return value of the method if <code>propertyResolved</code>
048:         * is <code>false</code>.</p>
049:         *
050:         * <p>The <code>CompositeELResolver</code> initializes the
051:         * <code>ELContext.propertyResolved</code> flag to <code>false</code>, and uses 
052:         * it as a stop condition for iterating through its component resolvers.</p>
053:         *
054:         * <p>The <code>ELContext.propertyResolved</code> flag is not used for the 
055:         * design-time methods {@link #getFeatureDescriptors} and
056:         * {@link #getCommonPropertyType}. Instead, results are collected and 
057:         * combined from all child <code>ELResolver</code>s for these methods.</p>
058:         *
059:         * @see ELContext
060:         * @see ELResolver
061:         * @since JSP 2.1
062:         */
063:        public class CompositeELResolver extends ELResolver {
064:
065:            /**
066:             * Adds the given resolver to the list of component resolvers.
067:             *
068:             * <p>Resolvers are consulted in the order in which they are added.</p>
069:             *
070:             * @param elResolver The component resolver to add.
071:             * @throws NullPointerException If the provided resolver is
072:             *     <code>null</code>.
073:             */
074:            public void add(ELResolver elResolver) {
075:
076:                if (elResolver == null) {
077:                    throw new NullPointerException();
078:                }
079:
080:                elResolvers.add(elResolver);
081:            }
082:
083:            /**
084:             * Attempts to resolve the given <code>property</code> object on the given
085:             * <code>base</code> object by querying all component resolvers.
086:             *
087:             * <p>If this resolver handles the given (base, property) pair, 
088:             * the <code>propertyResolved</code> property of the 
089:             * <code>ELContext</code> object must be set to <code>true</code>
090:             * by the resolver, before returning. If this property is not 
091:             * <code>true</code> after this method is called, the caller should ignore 
092:             * the return value.</p>
093:             *
094:             * <p>First, <code>propertyResolved</code> is set to <code>false</code> on
095:             * the provided <code>ELContext</code>.</p>
096:             *
097:             * <p>Next, for each component resolver in this composite:
098:             * <ol>
099:             *   <li>The <code>getValue()</code> method is called, passing in
100:             *       the provided <code>context</code>, <code>base</code> and 
101:             *       <code>property</code>.</li>
102:             *   <li>If the <code>ELContext</code>'s <code>propertyResolved</code>
103:             *       flag is <code>false</code> then iteration continues.</li>
104:             *   <li>Otherwise, iteration stops and no more component resolvers are
105:             *       considered. The value returned by <code>getValue()</code> is
106:             *       returned by this method.</li>
107:             * </ol></p>
108:             *
109:             * <p>If none of the component resolvers were able to perform this
110:             * operation, the value <code>null</code> is returned and the
111:             * <code>propertyResolved</code> flag remains set to 
112:             * <code>false</code></p>.
113:             *
114:             * <p>Any exception thrown by component resolvers during the iteration
115:             * is propagated to the caller of this method.</p>
116:             *
117:             * @param context The context of this evaluation.
118:             * @param base The base object whose property value is to be returned,
119:             *     or <code>null</code> to resolve a top-level variable.
120:             * @param property The property or variable to be resolved.
121:             * @return If the <code>propertyResolved</code> property of 
122:             *     <code>ELContext</code> was set to <code>true</code>, then
123:             *     the result of the variable or property resolution; otherwise
124:             *     undefined.
125:             * @throws NullPointerException if context is <code>null</code>
126:             * @throws PropertyNotFoundException if the given (base, property) pair
127:             *     is handled by this <code>ELResolver</code> but the specified
128:             *     variable or property does not exist or is not readable.
129:             * @throws ELException if an exception was thrown while performing
130:             *     the property or variable resolution. The thrown exception
131:             *     must be included as the cause property of this exception, if
132:             *     available.
133:             */
134:            public Object getValue(ELContext context, Object base,
135:                    Object property) {
136:                context.setPropertyResolved(false);
137:                int i = 0, len = this .elResolvers.size();
138:                ELResolver elResolver;
139:                Object value;
140:                while (i < len) {
141:                    elResolver = this .elResolvers.get(i);
142:                    value = elResolver.getValue(context, base, property);
143:                    if (context.isPropertyResolved()) {
144:                        return value;
145:                    }
146:                    i++;
147:                }
148:                return null;
149:            }
150:
151:            /**
152:             * For a given <code>base</code> and <code>property</code>, attempts to
153:             * identify the most general type that is acceptable for an object to be 
154:             * passed as the <code>value</code> parameter in a future call 
155:             * to the {@link #setValue} method. The result is obtained by 
156:             * querying all component resolvers.
157:             *
158:             * <p>If this resolver handles the given (base, property) pair, 
159:             * the <code>propertyResolved</code> property of the 
160:             * <code>ELContext</code> object must be set to <code>true</code>
161:             * by the resolver, before returning. If this property is not 
162:             * <code>true</code> after this method is called, the caller should ignore 
163:             * the return value.</p>
164:             *
165:             * <p>First, <code>propertyResolved</code> is set to <code>false</code> on
166:             * the provided <code>ELContext</code>.</p>
167:             *
168:             * <p>Next, for each component resolver in this composite:
169:             * <ol>
170:             *   <li>The <code>getType()</code> method is called, passing in
171:             *       the provided <code>context</code>, <code>base</code> and 
172:             *       <code>property</code>.</li>
173:             *   <li>If the <code>ELContext</code>'s <code>propertyResolved</code>
174:             *       flag is <code>false</code> then iteration continues.</li>
175:             *   <li>Otherwise, iteration stops and no more component resolvers are
176:             *       considered. The value returned by <code>getType()</code> is
177:             *       returned by this method.</li>
178:             * </ol></p>
179:             *
180:             * <p>If none of the component resolvers were able to perform this
181:             * operation, the value <code>null</code> is returned and the
182:             * <code>propertyResolved</code> flag remains set to 
183:             * <code>false</code></p>.
184:             *
185:             * <p>Any exception thrown by component resolvers during the iteration
186:             * is propagated to the caller of this method.</p>
187:             *
188:             * @param context The context of this evaluation.
189:             * @param base The base object whose property value is to be analyzed,
190:             *     or <code>null</code> to analyze a top-level variable.
191:             * @param property The property or variable to return the acceptable 
192:             *     type for.
193:             * @return If the <code>propertyResolved</code> property of 
194:             *     <code>ELContext</code> was set to <code>true</code>, then
195:             *     the most general acceptable type; otherwise undefined.
196:             * @throws NullPointerException if context is <code>null</code>
197:             * @throws PropertyNotFoundException if the given (base, property) pair
198:             *     is handled by this <code>ELResolver</code> but the specified
199:             *     variable or property does not exist or is not readable.
200:             * @throws ELException if an exception was thrown while performing
201:             *     the property or variable resolution. The thrown exception
202:             *     must be included as the cause property of this exception, if
203:             *     available.
204:             */
205:            public Class<?> getType(ELContext context, Object base,
206:                    Object property) {
207:                context.setPropertyResolved(false);
208:                int i = 0, len = this .elResolvers.size();
209:                ELResolver elResolver;
210:                Class<?> type;
211:                while (i < len) {
212:                    elResolver = this .elResolvers.get(i);
213:                    type = elResolver.getType(context, base, property);
214:                    if (context.isPropertyResolved()) {
215:                        return type;
216:                    }
217:                    i++;
218:                }
219:                return null;
220:            }
221:
222:            /**
223:             * Attempts to set the value of the given <code>property</code> 
224:             * object on the given <code>base</code> object. All component
225:             * resolvers are asked to attempt to set the value.
226:             *
227:             * <p>If this resolver handles the given (base, property) pair, 
228:             * the <code>propertyResolved</code> property of the 
229:             * <code>ELContext</code> object must be set to <code>true</code>
230:             * by the resolver, before returning. If this property is not 
231:             * <code>true</code> after this method is called, the caller can
232:             * safely assume no value has been set.</p>
233:             *
234:             * <p>First, <code>propertyResolved</code> is set to <code>false</code> on
235:             * the provided <code>ELContext</code>.</p>
236:             *
237:             * <p>Next, for each component resolver in this composite:
238:             * <ol>
239:             *   <li>The <code>setValue()</code> method is called, passing in
240:             *       the provided <code>context</code>, <code>base</code>, 
241:             *       <code>property</code> and <code>value</code>.</li>
242:             *   <li>If the <code>ELContext</code>'s <code>propertyResolved</code>
243:             *       flag is <code>false</code> then iteration continues.</li>
244:             *   <li>Otherwise, iteration stops and no more component resolvers are
245:             *       considered.</li>
246:             * </ol></p>
247:             *
248:             * <p>If none of the component resolvers were able to perform this
249:             * operation, the <code>propertyResolved</code> flag remains set to 
250:             * <code>false</code></p>.
251:             *
252:             * <p>Any exception thrown by component resolvers during the iteration
253:             * is propagated to the caller of this method.</p>
254:             *
255:             * @param context The context of this evaluation.
256:             * @param base The base object whose property value is to be set,
257:             *     or <code>null</code> to set a top-level variable.
258:             * @param property The property or variable to be set.
259:             * @param val The value to set the property or variable to.
260:             * @throws NullPointerException if context is <code>null</code>
261:             * @throws PropertyNotFoundException if the given (base, property) pair
262:             *     is handled by this <code>ELResolver</code> but the specified
263:             *     variable or property does not exist.
264:             * @throws PropertyNotWritableException if the given (base, property)
265:             *     pair is handled by this <code>ELResolver</code> but the specified
266:             *     variable or property is not writable.
267:             * @throws ELException if an exception was thrown while attempting to
268:             *     set the property or variable. The thrown exception
269:             *     must be included as the cause property of this exception, if
270:             *     available.
271:             */
272:            public void setValue(ELContext context, Object base,
273:                    Object property, Object val) {
274:                context.setPropertyResolved(false);
275:                int i = 0, len = this .elResolvers.size();
276:                ELResolver elResolver;
277:                while (i < len) {
278:                    elResolver = this .elResolvers.get(i);
279:                    elResolver.setValue(context, base, property, val);
280:                    if (context.isPropertyResolved()) {
281:                        return;
282:                    }
283:                    i++;
284:                }
285:            }
286:
287:            /**
288:             * For a given <code>base</code> and <code>property</code>, attempts to
289:             * determine whether a call to {@link #setValue} will always fail. The
290:             * result is obtained by querying all component resolvers.
291:             *
292:             * <p>If this resolver handles the given (base, property) pair, 
293:             * the <code>propertyResolved</code> property of the 
294:             * <code>ELContext</code> object must be set to <code>true</code>
295:             * by the resolver, before returning. If this property is not 
296:             * <code>true</code> after this method is called, the caller should ignore 
297:             * the return value.</p>
298:             *
299:             * <p>First, <code>propertyResolved</code> is set to <code>false</code> on
300:             * the provided <code>ELContext</code>.</p>
301:             *
302:             * <p>Next, for each component resolver in this composite:
303:             * <ol>
304:             *   <li>The <code>isReadOnly()</code> method is called, passing in
305:             *       the provided <code>context</code>, <code>base</code> and 
306:             *       <code>property</code>.</li>
307:             *   <li>If the <code>ELContext</code>'s <code>propertyResolved</code>
308:             *       flag is <code>false</code> then iteration continues.</li>
309:             *   <li>Otherwise, iteration stops and no more component resolvers are
310:             *       considered. The value returned by <code>isReadOnly()</code> is
311:             *       returned by this method.</li>
312:             * </ol></p>
313:             *
314:             * <p>If none of the component resolvers were able to perform this
315:             * operation, the value <code>false</code> is returned and the
316:             * <code>propertyResolved</code> flag remains set to 
317:             * <code>false</code></p>.
318:             *
319:             * <p>Any exception thrown by component resolvers during the iteration
320:             * is propagated to the caller of this method.</p>
321:             *
322:             * @param context The context of this evaluation.
323:             * @param base The base object whose property value is to be analyzed,
324:             *     or <code>null</code> to analyze a top-level variable.
325:             * @param property The property or variable to return the read-only status
326:             *     for.
327:             * @return If the <code>propertyResolved</code> property of 
328:             *     <code>ELContext</code> was set to <code>true</code>, then
329:             *     <code>true</code> if the property is read-only or
330:             *     <code>false</code> if not; otherwise undefined.
331:             * @throws NullPointerException if context is <code>null</code>
332:             * @throws PropertyNotFoundException if the given (base, property) pair
333:             *     is handled by this <code>ELResolver</code> but the specified
334:             *     variable or property does not exist.
335:             * @throws ELException if an exception was thrown while performing
336:             *     the property or variable resolution. The thrown exception
337:             *     must be included as the cause property of this exception, if
338:             *     available.
339:             */
340:            public boolean isReadOnly(ELContext context, Object base,
341:                    Object property) {
342:                context.setPropertyResolved(false);
343:                int i = 0, len = this .elResolvers.size();
344:                ELResolver elResolver;
345:                boolean readOnly;
346:                while (i < len) {
347:                    elResolver = this .elResolvers.get(i);
348:                    readOnly = elResolver.isReadOnly(context, base, property);
349:                    if (context.isPropertyResolved()) {
350:                        return readOnly;
351:                    }
352:                    i++;
353:                }
354:                return false; // Does not matter
355:            }
356:
357:            /**
358:             * Returns information about the set of variables or properties that 
359:             * can be resolved for the given <code>base</code> object. One use for
360:             * this method is to assist tools in auto-completion. The results are
361:             * collected from all component resolvers.
362:             *
363:             * <p>The <code>propertyResolved</code> property of the 
364:             * <code>ELContext</code> is not relevant to this method.
365:             * The results of all <code>ELResolver</code>s are concatenated.</p>
366:             *
367:             * <p>The <code>Iterator</code> returned is an iterator over the
368:             * collection of <code>FeatureDescriptor</code> objects returned by
369:             * the iterators returned by each component resolver's 
370:             * <code>getFeatureDescriptors</code> method. If <code>null</code> is 
371:             * returned by a resolver, it is skipped.</p>
372:             * 
373:             * @param context The context of this evaluation.
374:             * @param base The base object whose set of valid properties is to
375:             *     be enumerated, or <code>null</code> to enumerate the set of
376:             *     top-level variables that this resolver can evaluate.
377:             * @return An <code>Iterator</code> containing zero or more (possibly
378:             *     infinitely more) <code>FeatureDescriptor</code> objects, or 
379:             *     <code>null</code> if this resolver does not handle the given 
380:             *     <code>base</code> object or that the results are too complex to 
381:             *     represent with this method
382:             */
383:            public Iterator<FeatureDescriptor> getFeatureDescriptors(
384:                    ELContext context, Object base) {
385:                return new CompositeIterator(elResolvers.iterator(), context,
386:                        base);
387:            }
388:
389:            /**
390:             * Returns the most general type that this resolver accepts for the
391:             * <code>property</code> argument, given a <code>base</code> object.
392:             * One use for this method is to assist tools in auto-completion. The
393:             * result is obtained by querying all component resolvers.
394:             *
395:             * <p>The <code>Class</code> returned is the most specific class that is
396:             * a common superclass of all the classes returned by each component
397:             * resolver's <code>getCommonPropertyType</code> method. If 
398:             * <code>null</code> is returned by a resolver, it is skipped.</p>
399:             *
400:             * @param context The context of this evaluation.
401:             * @param base The base object to return the most general property
402:             *     type for, or <code>null</code> to enumerate the set of
403:             *     top-level variables that this resolver can evaluate.
404:             * @return <code>null</code> if this <code>ELResolver</code> does not
405:             *     know how to handle the given <code>base</code> object; otherwise
406:             *     <code>Object.class</code> if any type of <code>property</code>
407:             *     is accepted; otherwise the most general <code>property</code>
408:             *     type accepted for the given <code>base</code>.
409:             */
410:            public Class<?> getCommonPropertyType(ELContext context, Object base) {
411:                Class<?> commonPropertyType = null;
412:                Iterator<ELResolver> iter = elResolvers.iterator();
413:                while (iter.hasNext()) {
414:                    ELResolver elResolver = iter.next();
415:                    Class<?> type = elResolver.getCommonPropertyType(context,
416:                            base);
417:                    if (type == null) {
418:                        // skip this EL Resolver
419:                        continue;
420:                    } else if (commonPropertyType == null) {
421:                        commonPropertyType = type;
422:                    } else if (commonPropertyType.isAssignableFrom(type)) {
423:                        continue;
424:                    } else if (type.isAssignableFrom(commonPropertyType)) {
425:                        commonPropertyType = type;
426:                    } else {
427:                        // Don't have a commonPropertyType
428:                        return null;
429:                    }
430:                }
431:                return commonPropertyType;
432:            }
433:
434:            private final ArrayList<ELResolver> elResolvers = new ArrayList<ELResolver>();
435:
436:            private static class CompositeIterator implements 
437:                    Iterator<FeatureDescriptor> {
438:
439:                Iterator<ELResolver> compositeIter;
440:                Iterator<FeatureDescriptor> propertyIter;
441:                ELContext context;
442:                Object base;
443:
444:                CompositeIterator(Iterator<ELResolver> iter, ELContext context,
445:                        Object base) {
446:                    compositeIter = iter;
447:                    this .context = context;
448:                    this .base = base;
449:                }
450:
451:                public boolean hasNext() {
452:                    if (propertyIter == null || !propertyIter.hasNext()) {
453:                        while (compositeIter.hasNext()) {
454:                            ELResolver elResolver = compositeIter.next();
455:                            propertyIter = elResolver.getFeatureDescriptors(
456:                                    context, base);
457:                            if (propertyIter != null) {
458:                                return propertyIter.hasNext();
459:                            }
460:                        }
461:                        return false;
462:                    }
463:                    return propertyIter.hasNext();
464:                }
465:
466:                public FeatureDescriptor next() {
467:                    if (propertyIter == null || !propertyIter.hasNext()) {
468:                        while (compositeIter.hasNext()) {
469:                            ELResolver elResolver = compositeIter.next();
470:                            propertyIter = elResolver.getFeatureDescriptors(
471:                                    context, base);
472:                            if (propertyIter != null) {
473:                                return propertyIter.next();
474:                            }
475:                        }
476:                        return null;
477:                    }
478:                    return propertyIter.next();
479:                }
480:
481:                public void remove() {
482:                    throw new UnsupportedOperationException();
483:                }
484:            }
485:        }
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