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        Class effectiveTargetType = PlasticUtils.toWrapperType(targetType);
139
140        if (effectiveTargetType.isInstance(input))
141        {
142            return input;
143        }
144
145
146        return getTargetCoercion(effectiveTargetType).coerce(input);
147    }
148
149    @SuppressWarnings("unchecked")
150    public <S, T> Coercion<S, T> getCoercion(Class<S> sourceType, Class<T> targetType)
151    {
152        assert sourceType != null;
153        assert targetType != null;
154        Class effectiveSourceType = PlasticUtils.toWrapperType(sourceType);
155        Class effectiveTargetType = PlasticUtils.toWrapperType(targetType);
156
157        if (effectiveTargetType.isAssignableFrom(effectiveSourceType))
158        {
159            return NO_COERCION;
160        }
161
162        return getTargetCoercion(effectiveTargetType).getCoercion(effectiveSourceType);
163    }
164
165    @SuppressWarnings("unchecked")
166    public <S, T> String explain(Class<S> sourceType, Class<T> targetType)
167    {
168        assert sourceType != null;
169        assert targetType != null;
170        Class effectiveTargetType = PlasticUtils.toWrapperType(targetType);
171        Class effectiveSourceType = PlasticUtils.toWrapperType(sourceType);
172
173        // Is a coercion even necessary? Not if the target type is assignable from the
174        // input value.
175
176        if (effectiveTargetType.isAssignableFrom(effectiveSourceType))
177        {
178            return "";
179        }
180
181        return getTargetCoercion(effectiveTargetType).explain(effectiveSourceType);
182    }
183
184    private TargetCoercion getTargetCoercion(Class targetType)
185    {
186        try
187        {
188            acquireReadLock();
189
190            TargetCoercion tc = typeToTargetCoercion.get(targetType);
191
192            return tc != null ? tc : createAndStoreNewTargetCoercion(targetType);
193        } finally
194        {
195            releaseReadLock();
196        }
197    }
198
199    private TargetCoercion createAndStoreNewTargetCoercion(Class targetType)
200    {
201        try
202        {
203            upgradeReadLockToWriteLock();
204
205            // Inner check since some other thread may have beat us to it.
206
207            TargetCoercion tc = typeToTargetCoercion.get(targetType);
208
209            if (tc == null)
210            {
211                tc = new TargetCoercion(targetType);
212                typeToTargetCoercion.put(targetType, tc);
213            }
214
215            return tc;
216        } finally
217        {
218            downgradeWriteLockToReadLock();
219        }
220    }
221
222    public void clearCache()
223    {
224        try
225        {
226            acquireReadLock();
227
228            // There's no need to clear the typeToTargetCoercion map, as it is a WeakHashMap and
229            // will release the keys for classes that are no longer in existence. On the other hand,
230            // there's likely all sorts of references to unloaded classes inside each TargetCoercion's
231            // individual cache, so clear all those.
232
233            for (TargetCoercion tc : typeToTargetCoercion.values())
234            {
235                // Can tc ever be null?
236
237                tc.clearCache();
238            }
239        } finally
240        {
241            releaseReadLock();
242        }
243    }
244
245    /**
246     * Here's the real meat; we do a search of the space to find coercions, or a system of
247     * coercions, that accomplish
248     * the desired coercion.
249     * <p/>
250     * There's <strong>TREMENDOUS</strong> room to improve this algorithm. For example, inheritance lists could be
251     * cached. Further, there's probably more ways to early prune the search. However, even with dozens or perhaps
252     * hundreds of tuples, I suspect the search will still grind to a conclusion quickly.
253     * <p/>
254     * The order of operations should help ensure that the most efficient tuple chain is located. If you think about how
255     * tuples are added to the queue, there are two factors: size (the number of steps in the coercion) and
256     * "class distance" (that is, number of steps up the inheritance hiearchy). All the appropriate 1 step coercions
257     * will be considered first, in class distance order. Along the way, we'll queue up all the 2 step coercions, again
258     * in class distance order. By the time we reach some of those, we'll have begun queueing up the 3 step coercions, and
259     * so forth, until we run out of input tuples we can use to fabricate multi-step compound coercions, or reach a
260     * final response.
261     * <p/>
262     * This does create a good number of short lived temporary objects (the compound tuples), but that's what the GC is
263     * really good at.
264     *
265     * @param sourceType
266     * @param targetType
267     * @return coercer from sourceType to targetType
268     */
269    @SuppressWarnings("unchecked")
270    private Coercion findOrCreateCoercion(Class sourceType, Class targetType)
271    {
272        if (sourceType == Void.class)
273        {
274            return searchForNullCoercion(targetType);
275        }
276
277        // These are instance variables because this method may be called concurrently.
278        // On a true race, we may go to the work of seeking out and/or fabricating
279        // a tuple twice, but it's more likely that different threads are looking
280        // for different source/target coercions.
281
282        Set<CoercionTuple> consideredTuples = CollectionFactory.newSet();
283        LinkedList<CoercionTuple> queue = CollectionFactory.newLinkedList();
284
285        seedQueue(sourceType, targetType, consideredTuples, queue);
286
287        while (!queue.isEmpty())
288        {
289            CoercionTuple tuple = queue.removeFirst();
290
291            // If the tuple results in a value type that is assignable to the desired target type,
292            // we're done! Later, we may add a concept of "cost" (i.e. number of steps) or
293            // "quality" (how close is the tuple target type to the desired target type). Cost
294            // is currently implicit, as compound tuples are stored deeper in the queue,
295            // so simpler coercions will be located earlier.
296
297            Class tupleTargetType = tuple.getTargetType();
298
299            if (targetType.isAssignableFrom(tupleTargetType))
300            {
301                return tuple.getCoercion();
302            }
303
304            // So .. this tuple doesn't get us directly to the target type.
305            // However, it *may* get us part of the way. Each of these
306            // represents a coercion from the source type to an intermediate type.
307            // Now we're going to look for conversions from the intermediate type
308            // to some other type.
309
310            queueIntermediates(sourceType, targetType, tuple, consideredTuples, queue);
311        }
312
313        // Not found anywhere. Identify the source and target type and a (sorted) list of
314        // all the known coercions.
315
316        throw new UnknownValueException(String.format("Could not find a coercion from type %s to type %s.",
317                sourceType.getName(), targetType.getName()), buildCoercionCatalog());
318    }
319
320    /**
321     * Coercion from null is special; we match based on the target type and its not a spanning
322     * search. In many cases, we
323     * return a pass-thru that leaves the value as null.
324     *
325     * @param targetType
326     *         desired type
327     * @return the coercion
328     */
329    private Coercion searchForNullCoercion(Class targetType)
330    {
331        List<CoercionTuple> tuples = getTuples(Void.class, targetType);
332
333        for (CoercionTuple tuple : tuples)
334        {
335            Class tupleTargetType = tuple.getTargetType();
336
337            if (targetType.equals(tupleTargetType))
338                return tuple.getCoercion();
339        }
340
341        // Typical case: no match, this coercion passes the null through
342        // as null.
343
344        return COERCION_NULL_TO_OBJECT;
345    }
346
347    /**
348     * Builds a string listing all the coercions configured for the type coercer, sorted
349     * alphabetically.
350     */
351    @SuppressWarnings("unchecked")
352    private AvailableValues buildCoercionCatalog()
353    {
354        List<CoercionTuple> masterList = CollectionFactory.newList();
355
356        for (List<CoercionTuple> list : sourceTypeToTuple.values())
357        {
358            masterList.addAll(list);
359        }
360
361        return new AvailableValues("Configured coercions", masterList);
362    }
363
364    /**
365     * Seeds the pool with the initial set of coercions for the given type.
366     */
367    private void seedQueue(Class sourceType, Class targetType, Set<CoercionTuple> consideredTuples,
368                           LinkedList<CoercionTuple> queue)
369    {
370        // Work from the source type up looking for tuples
371
372        for (Class c : new InheritanceSearch(sourceType))
373        {
374            List<CoercionTuple> tuples = getTuples(c, targetType);
375
376            if (tuples == null)
377            {
378                continue;
379            }
380
381            for (CoercionTuple tuple : tuples)
382            {
383                queue.addLast(tuple);
384                consideredTuples.add(tuple);
385            }
386
387            // Don't pull in Object -> type coercions when doing
388            // a search from null.
389
390            if (sourceType == Void.class)
391            {
392                return;
393            }
394        }
395    }
396
397    /**
398     * Creates and adds to the pool a new set of coercions based on an intermediate tuple. Adds
399     * compound coercion tuples
400     * to the end of the queue.
401     *
402     * @param sourceType
403     *         the source type of the coercion
404     * @param targetType
405     *         TODO
406     * @param intermediateTuple
407     *         a tuple that converts from the source type to some intermediate type (that is not
408     *         assignable to the target type)
409     * @param consideredTuples
410     *         set of tuples that have already been added to the pool (directly, or as a compound
411     *         coercion)
412     * @param queue
413     *         the work queue of tuples
414     */
415    @SuppressWarnings("unchecked")
416    private void queueIntermediates(Class sourceType, Class targetType, CoercionTuple intermediateTuple,
417                                    Set<CoercionTuple> consideredTuples, LinkedList<CoercionTuple> queue)
418    {
419        Class intermediateType = intermediateTuple.getTargetType();
420
421        for (Class c : new InheritanceSearch(intermediateType))
422        {
423            for (CoercionTuple tuple : getTuples(c, targetType))
424            {
425                if (consideredTuples.contains(tuple))
426                {
427                    continue;
428                }
429
430                Class newIntermediateType = tuple.getTargetType();
431
432                // If this tuple is for coercing from an intermediate type back towards our
433                // initial source type, then ignore it. This should only be an optimization,
434                // as branches that loop back towards the source type will
435                // eventually be considered and discarded.
436
437                if (sourceType.isAssignableFrom(newIntermediateType))
438                {
439                    continue;
440                }
441
442                // The intermediateTuple coercer gets from S --> I1 (an intermediate type).
443                // The current tuple's coercer gets us from I2 --> X. where I2 is assignable
444                // from I1 (i.e., I2 is a superclass/superinterface of I1) and X is a new
445                // intermediate type, hopefully closer to our eventual target type.
446
447                Coercion compoundCoercer = new CompoundCoercion(intermediateTuple.getCoercion(), tuple.getCoercion());
448
449                CoercionTuple compoundTuple = new CoercionTuple(sourceType, newIntermediateType, compoundCoercer, false);
450
451                // So, every tuple that is added to the queue can take as input the sourceType.
452                // The target type may be another intermediate type, or may be something
453                // assignable to the target type, which will bring the search to a successful
454                // conclusion.
455
456                queue.addLast(compoundTuple);
457                consideredTuples.add(tuple);
458            }
459        }
460    }
461
462    /**
463     * Returns a non-null list of the tuples from the source type.
464     *
465     * @param sourceType
466     *         used to locate tuples
467     * @param targetType
468     *         used to add synthetic tuples
469     * @return non-null list of tuples
470     */
471    private List<CoercionTuple> getTuples(Class sourceType, Class targetType)
472    {
473        List<CoercionTuple> tuples = sourceTypeToTuple.get(sourceType);
474
475        if (tuples == null)
476        {
477            tuples = Collections.emptyList();
478        }
479
480        // So, when we see String and an Enum type, we add an additional synthetic tuple to the end
481        // of the real list. This is the easiest way to accomplish this is a thread-safe and class-reloading
482        // safe way (i.e., what if the Enum is defined by a class loader that gets discarded?  Don't want to cause
483        // memory leaks by retaining an instance). In any case, there are edge cases where we may create
484        // the tuple unnecessarily (such as when an explicit string-to-enum coercion is part of the TypeCoercer
485        // configuration), but on the whole, this is cheap and works.
486
487        if (sourceType == String.class && Enum.class.isAssignableFrom(targetType))
488        {
489            tuples = extend(tuples, new CoercionTuple(sourceType, targetType, new StringToEnumCoercion(targetType)));
490        }
491
492        return tuples;
493    }
494
495    private static <T> List<T> extend(List<T> list, T extraValue)
496    {
497        return F.flow(list).append(extraValue).toList();
498    }
499}