001// Copyright 2006, 2007, 2008, 2010, 2012 The Apache Software Foundation
002//
003// Licensed under the Apache License, Version 2.0 (the "License");
004// you may not use this file except in compliance with the License.
005// You may obtain a copy of the License at
006//
007// http://www.apache.org/licenses/LICENSE-2.0
008//
009// Unless required by applicable law or agreed to in writing, software
010// distributed under the License is distributed on an "AS IS" BASIS,
011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012// See the License for the specific language governing permissions and
013// limitations under the License.
014
015package org.apache.tapestry5.ioc.internal.services;
016
017import org.apache.tapestry5.func.F;
018import org.apache.tapestry5.ioc.internal.util.CollectionFactory;
019import org.apache.tapestry5.ioc.internal.util.InheritanceSearch;
020import org.apache.tapestry5.ioc.internal.util.InternalUtils;
021import org.apache.tapestry5.ioc.internal.util.LockSupport;
022import org.apache.tapestry5.ioc.services.Coercion;
023import org.apache.tapestry5.ioc.services.CoercionTuple;
024import org.apache.tapestry5.ioc.services.TypeCoercer;
025import org.apache.tapestry5.ioc.util.AvailableValues;
026import org.apache.tapestry5.ioc.util.UnknownValueException;
027import org.apache.tapestry5.plastic.PlasticUtils;
028import org.apache.tapestry5.util.StringToEnumCoercion;
029
030import java.util.*;
031
032@SuppressWarnings("all")
033public class TypeCoercerImpl extends LockSupport implements TypeCoercer
034{
035    // Constructed from the service's configuration.
036
037    private final Map<Class, List<CoercionTuple>> sourceTypeToTuple = CollectionFactory.newMap();
038
039    /**
040     * A coercion to a specific target type. Manages a cache of coercions to specific types.
041     */
042    private class TargetCoercion
043    {
044        private final Class type;
045
046        private final Map<Class, Coercion> cache = CollectionFactory.newConcurrentMap();
047
048        TargetCoercion(Class type)
049        {
050            this.type = type;
051        }
052
053        void clearCache()
054        {
055            cache.clear();
056        }
057
058        Object coerce(Object input)
059        {
060            Class sourceType = input != null ? input.getClass() : Void.class;
061
062            if (type.isAssignableFrom(sourceType))
063            {
064                return input;
065            }
066
067            Coercion c = getCoercion(sourceType);
068
069            try
070            {
071                return type.cast(c.coerce(input));
072            } catch (Exception ex)
073            {
074                throw new RuntimeException(ServiceMessages.failedCoercion(input, type, c, ex), ex);
075            }
076        }
077
078        String explain(Class sourceType)
079        {
080            return getCoercion(sourceType).toString();
081        }
082
083        private Coercion getCoercion(Class sourceType)
084        {
085            Coercion c = cache.get(sourceType);
086
087            if (c == null)
088            {
089                c = findOrCreateCoercion(sourceType, type);
090                cache.put(sourceType, c);
091            }
092
093            return c;
094        }
095    }
096
097    /**
098     * Map from a target type to a TargetCoercion for that type.
099     */
100    private final Map<Class, TargetCoercion> typeToTargetCoercion = new WeakHashMap<Class, TargetCoercion>();
101
102    private static final Coercion NO_COERCION = new Coercion<Object, Object>()
103    {
104        public Object coerce(Object input)
105        {
106            return input;
107        }
108    };
109
110    private static final Coercion COERCION_NULL_TO_OBJECT = new Coercion<Void, Object>()
111    {
112        public Object coerce(Void input)
113        {
114            return null;
115        }
116
117        @Override
118        public String toString()
119        {
120            return "null --> null";
121        }
122    };
123
124    public TypeCoercerImpl(Collection<CoercionTuple> tuples)
125    {
126        for (CoercionTuple tuple : tuples)
127        {
128            Class key = tuple.getSourceType();
129
130            InternalUtils.addToMapList(sourceTypeToTuple, key, tuple);
131        }
132    }
133
134    @SuppressWarnings("unchecked")
135    public Object coerce(Object input, Class targetType)
136    {
137        assert targetType != null;
138
139        Class effectiveTargetType = PlasticUtils.toWrapperType(targetType);
140
141        if (effectiveTargetType.isInstance(input))
142        {
143            return input;
144        }
145
146
147        return getTargetCoercion(effectiveTargetType).coerce(input);
148    }
149
150    @SuppressWarnings("unchecked")
151    public <S, T> Coercion<S, T> getCoercion(Class<S> sourceType, Class<T> targetType)
152    {
153        assert sourceType != null;
154        assert targetType != null;
155
156        Class effectiveSourceType = PlasticUtils.toWrapperType(sourceType);
157        Class effectiveTargetType = PlasticUtils.toWrapperType(targetType);
158
159        if (effectiveTargetType.isAssignableFrom(effectiveSourceType))
160        {
161            return NO_COERCION;
162        }
163
164        return getTargetCoercion(effectiveTargetType).getCoercion(effectiveSourceType);
165    }
166
167    @SuppressWarnings("unchecked")
168    public <S, T> String explain(Class<S> sourceType, Class<T> targetType)
169    {
170        assert sourceType != null;
171        assert targetType != null;
172
173        Class effectiveTargetType = PlasticUtils.toWrapperType(targetType);
174        Class effectiveSourceType = PlasticUtils.toWrapperType(sourceType);
175
176        // Is a coercion even necessary? Not if the target type is assignable from the
177        // input value.
178
179        if (effectiveTargetType.isAssignableFrom(effectiveSourceType))
180        {
181            return "";
182        }
183
184        return getTargetCoercion(effectiveTargetType).explain(effectiveSourceType);
185    }
186
187    private TargetCoercion getTargetCoercion(Class targetType)
188    {
189        try
190        {
191            acquireReadLock();
192
193            TargetCoercion tc = typeToTargetCoercion.get(targetType);
194
195            return tc != null ? tc : createAndStoreNewTargetCoercion(targetType);
196        } finally
197        {
198            releaseReadLock();
199        }
200    }
201
202    private TargetCoercion createAndStoreNewTargetCoercion(Class targetType)
203    {
204        try
205        {
206            upgradeReadLockToWriteLock();
207
208            // Inner check since some other thread may have beat us to it.
209
210            TargetCoercion tc = typeToTargetCoercion.get(targetType);
211
212            if (tc == null)
213            {
214                tc = new TargetCoercion(targetType);
215                typeToTargetCoercion.put(targetType, tc);
216            }
217
218            return tc;
219        } finally
220        {
221            downgradeWriteLockToReadLock();
222        }
223    }
224
225    public void clearCache()
226    {
227        try
228        {
229            acquireReadLock();
230
231            // There's no need to clear the typeToTargetCoercion map, as it is a WeakHashMap and
232            // will release the keys for classes that are no longer in existence. On the other hand,
233            // there's likely all sorts of references to unloaded classes inside each TargetCoercion's
234            // individual cache, so clear all those.
235
236            for (TargetCoercion tc : typeToTargetCoercion.values())
237            {
238                // Can tc ever be null?
239
240                tc.clearCache();
241            }
242        } finally
243        {
244            releaseReadLock();
245        }
246    }
247
248    /**
249     * Here's the real meat; we do a search of the space to find coercions, or a system of
250     * coercions, that accomplish
251     * the desired coercion.
252     * <p/>
253     * There's <strong>TREMENDOUS</strong> room to improve this algorithm. For example, inheritance lists could be
254     * cached. Further, there's probably more ways to early prune the search. However, even with dozens or perhaps
255     * hundreds of tuples, I suspect the search will still grind to a conclusion quickly.
256     * <p/>
257     * The order of operations should help ensure that the most efficient tuple chain is located. If you think about how
258     * tuples are added to the queue, there are two factors: size (the number of steps in the coercion) and
259     * "class distance" (that is, number of steps up the inheritance hiearchy). All the appropriate 1 step coercions
260     * will be considered first, in class distance order. Along the way, we'll queue up all the 2 step coercions, again
261     * in class distance order. By the time we reach some of those, we'll have begun queueing up the 3 step coercions, and
262     * so forth, until we run out of input tuples we can use to fabricate multi-step compound coercions, or reach a
263     * final response.
264     * <p/>
265     * This does create a good number of short lived temporary objects (the compound tuples), but that's what the GC is
266     * really good at.
267     *
268     * @param sourceType
269     * @param targetType
270     * @return coercer from sourceType to targetType
271     */
272    @SuppressWarnings("unchecked")
273    private Coercion findOrCreateCoercion(Class sourceType, Class targetType)
274    {
275        if (sourceType == Void.class)
276        {
277            return searchForNullCoercion(targetType);
278        }
279
280        // These are instance variables because this method may be called concurrently.
281        // On a true race, we may go to the work of seeking out and/or fabricating
282        // a tuple twice, but it's more likely that different threads are looking
283        // for different source/target coercions.
284
285        Set<CoercionTuple> consideredTuples = CollectionFactory.newSet();
286        LinkedList<CoercionTuple> queue = CollectionFactory.newLinkedList();
287
288        seedQueue(sourceType, targetType, consideredTuples, queue);
289
290        while (!queue.isEmpty())
291        {
292            CoercionTuple tuple = queue.removeFirst();
293
294            // If the tuple results in a value type that is assignable to the desired target type,
295            // we're done! Later, we may add a concept of "cost" (i.e. number of steps) or
296            // "quality" (how close is the tuple target type to the desired target type). Cost
297            // is currently implicit, as compound tuples are stored deeper in the queue,
298            // so simpler coercions will be located earlier.
299
300            Class tupleTargetType = tuple.getTargetType();
301
302            if (targetType.isAssignableFrom(tupleTargetType))
303            {
304                return tuple.getCoercion();
305            }
306
307            // So .. this tuple doesn't get us directly to the target type.
308            // However, it *may* get us part of the way. Each of these
309            // represents a coercion from the source type to an intermediate type.
310            // Now we're going to look for conversions from the intermediate type
311            // to some other type.
312
313            queueIntermediates(sourceType, targetType, tuple, consideredTuples, queue);
314        }
315
316        // Not found anywhere. Identify the source and target type and a (sorted) list of
317        // all the known coercions.
318
319        throw new UnknownValueException(String.format("Could not find a coercion from type %s to type %s.",
320                sourceType.getName(), targetType.getName()), buildCoercionCatalog());
321    }
322
323    /**
324     * Coercion from null is special; we match based on the target type and its not a spanning
325     * search. In many cases, we
326     * return a pass-thru that leaves the value as null.
327     *
328     * @param targetType
329     *         desired type
330     * @return the coercion
331     */
332    private Coercion searchForNullCoercion(Class targetType)
333    {
334        List<CoercionTuple> tuples = getTuples(Void.class, targetType);
335
336        for (CoercionTuple tuple : tuples)
337        {
338            Class tupleTargetType = tuple.getTargetType();
339
340            if (targetType.equals(tupleTargetType))
341                return tuple.getCoercion();
342        }
343
344        // Typical case: no match, this coercion passes the null through
345        // as null.
346
347        return COERCION_NULL_TO_OBJECT;
348    }
349
350    /**
351     * Builds a string listing all the coercions configured for the type coercer, sorted
352     * alphabetically.
353     */
354    @SuppressWarnings("unchecked")
355    private AvailableValues buildCoercionCatalog()
356    {
357        List<CoercionTuple> masterList = CollectionFactory.newList();
358
359        for (List<CoercionTuple> list : sourceTypeToTuple.values())
360        {
361            masterList.addAll(list);
362        }
363
364        return new AvailableValues("Configured coercions", masterList);
365    }
366
367    /**
368     * Seeds the pool with the initial set of coercions for the given type.
369     */
370    private void seedQueue(Class sourceType, Class targetType, Set<CoercionTuple> consideredTuples,
371                           LinkedList<CoercionTuple> queue)
372    {
373        // Work from the source type up looking for tuples
374
375        for (Class c : new InheritanceSearch(sourceType))
376        {
377            List<CoercionTuple> tuples = getTuples(c, targetType);
378
379            if (tuples == null)
380            {
381                continue;
382            }
383
384            for (CoercionTuple tuple : tuples)
385            {
386                queue.addLast(tuple);
387                consideredTuples.add(tuple);
388            }
389
390            // Don't pull in Object -> type coercions when doing
391            // a search from null.
392
393            if (sourceType == Void.class)
394            {
395                return;
396            }
397        }
398    }
399
400    /**
401     * Creates and adds to the pool a new set of coercions based on an intermediate tuple. Adds
402     * compound coercion tuples
403     * to the end of the queue.
404     *
405     * @param sourceType
406     *         the source type of the coercion
407     * @param targetType
408     *         TODO
409     * @param intermediateTuple
410     *         a tuple that converts from the source type to some intermediate type (that is not
411     *         assignable to the target type)
412     * @param consideredTuples
413     *         set of tuples that have already been added to the pool (directly, or as a compound
414     *         coercion)
415     * @param queue
416     *         the work queue of tuples
417     */
418    @SuppressWarnings("unchecked")
419    private void queueIntermediates(Class sourceType, Class targetType, CoercionTuple intermediateTuple,
420                                    Set<CoercionTuple> consideredTuples, LinkedList<CoercionTuple> queue)
421    {
422        Class intermediateType = intermediateTuple.getTargetType();
423
424        for (Class c : new InheritanceSearch(intermediateType))
425        {
426            for (CoercionTuple tuple : getTuples(c, targetType))
427            {
428                if (consideredTuples.contains(tuple))
429                {
430                    continue;
431                }
432
433                Class newIntermediateType = tuple.getTargetType();
434
435                // If this tuple is for coercing from an intermediate type back towards our
436                // initial source type, then ignore it. This should only be an optimization,
437                // as branches that loop back towards the source type will
438                // eventually be considered and discarded.
439
440                if (sourceType.isAssignableFrom(newIntermediateType))
441                {
442                    continue;
443                }
444
445                // The intermediateTuple coercer gets from S --> I1 (an intermediate type).
446                // The current tuple's coercer gets us from I2 --> X. where I2 is assignable
447                // from I1 (i.e., I2 is a superclass/superinterface of I1) and X is a new
448                // intermediate type, hopefully closer to our eventual target type.
449
450                Coercion compoundCoercer = new CompoundCoercion(intermediateTuple.getCoercion(), tuple.getCoercion());
451
452                CoercionTuple compoundTuple = new CoercionTuple(sourceType, newIntermediateType, compoundCoercer, false);
453
454                // So, every tuple that is added to the queue can take as input the sourceType.
455                // The target type may be another intermediate type, or may be something
456                // assignable to the target type, which will bring the search to a successful
457                // conclusion.
458
459                queue.addLast(compoundTuple);
460                consideredTuples.add(tuple);
461            }
462        }
463    }
464
465    /**
466     * Returns a non-null list of the tuples from the source type.
467     *
468     * @param sourceType
469     *         used to locate tuples
470     * @param targetType
471     *         used to add synthetic tuples
472     * @return non-null list of tuples
473     */
474    private List<CoercionTuple> getTuples(Class sourceType, Class targetType)
475    {
476        List<CoercionTuple> tuples = sourceTypeToTuple.get(sourceType);
477
478        if (tuples == null)
479        {
480            tuples = Collections.emptyList();
481        }
482
483        // So, when we see String and an Enum type, we add an additional synthetic tuple to the end
484        // of the real list. This is the easiest way to accomplish this is a thread-safe and class-reloading
485        // safe way (i.e., what if the Enum is defined by a class loader that gets discarded?  Don't want to cause
486        // memory leaks by retaining an instance). In any case, there are edge cases where we may create
487        // the tuple unnecessarily (such as when an explicit string-to-enum coercion is part of the TypeCoercer
488        // configuration), but on the whole, this is cheap and works.
489
490        if (sourceType == String.class && Enum.class.isAssignableFrom(targetType))
491        {
492            tuples = extend(tuples, new CoercionTuple(sourceType, targetType, new StringToEnumCoercion(targetType)));
493        }
494
495        return tuples;
496    }
497
498    private static <T> List<T> extend(List<T> list, T extraValue)
499    {
500        return F.flow(list).append(extraValue).toList();
501    }
502}