    001// Licensed under the Apache License, Version 2.0 (the "License");
    002// you may not use this file except in compliance with the License.
    003// You may obtain a copy of the License at
    004//
    005// http://www.apache.org/licenses/LICENSE-2.0
    006//
    007// Unless required by applicable law or agreed to in writing, software
    008// distributed under the License is distributed on an "AS IS" BASIS,
    009// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    010// See the License for the specific language governing permissions and
    011// limitations under the License.
    012
    013package org.apache.tapestry5.ioc.internal.services;
    014
    015import org.apache.tapestry5.func.F;
    016import org.apache.tapestry5.ioc.internal.util.CollectionFactory;
    017import org.apache.tapestry5.ioc.internal.util.InheritanceSearch;
    018import org.apache.tapestry5.ioc.internal.util.InternalCommonsUtils;
    019import org.apache.tapestry5.ioc.internal.util.LockSupport;
    020import org.apache.tapestry5.ioc.services.Coercion;
    021import org.apache.tapestry5.ioc.services.CoercionTuple;
    022import org.apache.tapestry5.ioc.services.TypeCoercer;
    023import org.apache.tapestry5.ioc.util.AvailableValues;
    024import org.apache.tapestry5.ioc.util.UnknownValueException;
    025import org.apache.tapestry5.plastic.PlasticUtils;
    026import org.apache.tapestry5.util.StringToEnumCoercion;
    027
    028import java.util.*;
    029
    030@SuppressWarnings("all")
    031public class TypeCoercerImpl extends LockSupport implements TypeCoercer
    032{
    033    // Constructed from the service's configuration.
    034
    035    private final Map<Class, List<CoercionTuple>> sourceTypeToTuple = CollectionFactory.newMap();
    036
    037    /**
    038     * A coercion to a specific target type. Manages a cache of coercions to specific types.
    039     */
    040    private class TargetCoercion
    041    {
    042        private final Class type;
    043
    044        private final Map<Class, Coercion> cache = CollectionFactory.newConcurrentMap();
    045
    046        TargetCoercion(Class type)
    047        {
    048            this.type = type;
    049        }
    050
    051        void clearCache()
    052        {
    053            cache.clear();
    054        }
    055
    056        Object coerce(Object input)
    057        {
    058            Class sourceType = input != null ? input.getClass() : Void.class;
    059
    060            if (type.isAssignableFrom(sourceType))
    061            {
    062                return input;
    063            }
    064
    065            Coercion c = getCoercion(sourceType);
    066
    067            try
    068            {
    069                return type.cast(c.coerce(input));
    070            } catch (Exception ex)
    071            {
    072                throw new RuntimeException(ServiceMessages.failedCoercion(input, type, c, ex), ex);
    073            }
    074        }
    075
    076        String explain(Class sourceType)
    077        {
    078            return getCoercion(sourceType).toString();
    079        }
    080
    081        private Coercion getCoercion(Class sourceType)
    082        {
    083            Coercion c = cache.get(sourceType);
    084
    085            if (c == null)
    086            {
    087                c = findOrCreateCoercion(sourceType, type);
    088                cache.put(sourceType, c);
    089            }
    090
    091            return c;
    092        }
    093    }
    094
    095    /**
    096     * Map from a target type to a TargetCoercion for that type.
    097     */
    098    private final Map<Class, TargetCoercion> typeToTargetCoercion = new WeakHashMap<Class, TargetCoercion>();
    099
    100    private static final Coercion NO_COERCION = new Coercion<Object, Object>()
    101    {
    102        @Override
    103        public Object coerce(Object input)
    104        {
    105            return input;
    106        }
    107    };
    108
    109    private static final Coercion COERCION_NULL_TO_OBJECT = new Coercion<Void, Object>()
    110    {
    111        @Override
    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    private static final Coercion COERCION_ENUM_TO_STRING = new Coercion<Enum, String>()
    125    {
    126        @Override
    127        public String coerce(Enum input)
    128        {
    129            return input.name();
    130        }
    131    };
    132
    133    public TypeCoercerImpl(Collection<CoercionTuple> tuples)
    134    {
    135        for (CoercionTuple tuple : tuples)
    136        {
    137            Class key = tuple.getSourceType();
    138
    139            InternalCommonsUtils.addToMapList(sourceTypeToTuple, key, tuple);
    140        }
    141    }
    142
    143    @Override
    144    @SuppressWarnings("unchecked")
    145    public Object coerce(Object input, Class targetType)
    146    {
    147        assert targetType != null;
    148
    149        Class effectiveTargetType = PlasticUtils.toWrapperType(targetType);
    150
    151        if (effectiveTargetType.isInstance(input))
    152        {
    153            return input;
    154        }
    155
    156
    157        return getTargetCoercion(effectiveTargetType).coerce(input);
    158    }
    159
    160    @Override
    161    @SuppressWarnings("unchecked")
    162    public <S, T> Coercion<S, T> getCoercion(Class<S> sourceType, Class<T> targetType)
    163    {
    164        assert sourceType != null;
    165        assert targetType != null;
    166
    167        Class effectiveSourceType = PlasticUtils.toWrapperType(sourceType);
    168        Class effectiveTargetType = PlasticUtils.toWrapperType(targetType);
    169
    170        if (effectiveTargetType.isAssignableFrom(effectiveSourceType))
    171        {
    172            return NO_COERCION;
    173        }
    174
    175        return getTargetCoercion(effectiveTargetType).getCoercion(effectiveSourceType);
    176    }
    177
    178    @Override
    179    @SuppressWarnings("unchecked")
    180    public <S, T> String explain(Class<S> sourceType, Class<T> targetType)
    181    {
    182        assert sourceType != null;
    183        assert targetType != null;
    184
    185        Class effectiveTargetType = PlasticUtils.toWrapperType(targetType);
    186        Class effectiveSourceType = PlasticUtils.toWrapperType(sourceType);
    187
    188        // Is a coercion even necessary? Not if the target type is assignable from the
    189        // input value.
    190
    191        if (effectiveTargetType.isAssignableFrom(effectiveSourceType))
    192        {
    193            return "";
    194        }
    195
    196        return getTargetCoercion(effectiveTargetType).explain(effectiveSourceType);
    197    }
    198
    199    private TargetCoercion getTargetCoercion(Class targetType)
    200    {
    201        try
    202        {
    203            acquireReadLock();
    204
    205            TargetCoercion tc = typeToTargetCoercion.get(targetType);
    206
    207            return tc != null ? tc : createAndStoreNewTargetCoercion(targetType);
    208        } finally
    209        {
    210            releaseReadLock();
    211        }
    212    }
    213
    214    private TargetCoercion createAndStoreNewTargetCoercion(Class targetType)
    215    {
    216        try
    217        {
    218            upgradeReadLockToWriteLock();
    219
    220            // Inner check since some other thread may have beat us to it.
    221
    222            TargetCoercion tc = typeToTargetCoercion.get(targetType);
    223
    224            if (tc == null)
    225            {
    226                tc = new TargetCoercion(targetType);
    227                typeToTargetCoercion.put(targetType, tc);
    228            }
    229
    230            return tc;
    231        } finally
    232        {
    233            downgradeWriteLockToReadLock();
    234        }
    235    }
    236
    237    @Override
    238    public void clearCache()
    239    {
    240        try
    241        {
    242            acquireReadLock();
    243
    244            // There's no need to clear the typeToTargetCoercion map, as it is a WeakHashMap and
    245            // will release the keys for classes that are no longer in existence. On the other hand,
    246            // there's likely all sorts of references to unloaded classes inside each TargetCoercion's
    247            // individual cache, so clear all those.
    248
    249            for (TargetCoercion tc : typeToTargetCoercion.values())
    250            {
    251                // Can tc ever be null?
    252
    253                tc.clearCache();
    254            }
    255        } finally
    256        {
    257            releaseReadLock();
    258        }
    259    }
    260
    261    /**
    262     * Here's the real meat; we do a search of the space to find coercions, or a system of
    263     * coercions, that accomplish
    264     * the desired coercion.
    265     *
    266     * There's <strong>TREMENDOUS</strong> room to improve this algorithm. For example, inheritance lists could be
    267     * cached. Further, there's probably more ways to early prune the search. However, even with dozens or perhaps
    268     * hundreds of tuples, I suspect the search will still grind to a conclusion quickly.
    269     *
    270     * The order of operations should help ensure that the most efficient tuple chain is located. If you think about how
    271     * tuples are added to the queue, there are two factors: size (the number of steps in the coercion) and
    272     * "class distance" (that is, number of steps up the inheritance hiearchy). All the appropriate 1 step coercions
    273     * will be considered first, in class distance order. Along the way, we'll queue up all the 2 step coercions, again
    274     * in class distance order. By the time we reach some of those, we'll have begun queueing up the 3 step coercions, and
    275     * so forth, until we run out of input tuples we can use to fabricate multi-step compound coercions, or reach a
    276     * final response.
    277     *
    278     * This does create a good number of short lived temporary objects (the compound tuples), but that's what the GC is
    279     * really good at.
    280     *
    281     * @param sourceType
    282     * @param targetType
    283     * @return coercer from sourceType to targetType
    284     */
    285    @SuppressWarnings("unchecked")
    286    private Coercion findOrCreateCoercion(Class sourceType, Class targetType)
    287    {
    288        if (sourceType == Void.class)
    289        {
    290            return searchForNullCoercion(targetType);
    291        }
    292
    293        // These are instance variables because this method may be called concurrently.
    294        // On a true race, we may go to the work of seeking out and/or fabricating
    295        // a tuple twice, but it's more likely that different threads are looking
    296        // for different source/target coercions.
    297
    298        Set<CoercionTuple> consideredTuples = CollectionFactory.newSet();
    299        LinkedList<CoercionTuple> queue = CollectionFactory.newLinkedList();
    300
    301        seedQueue(sourceType, targetType, consideredTuples, queue);
    302
    303        while (!queue.isEmpty())
    304        {
    305            CoercionTuple tuple = queue.removeFirst();
    306
    307            // If the tuple results in a value type that is assignable to the desired target type,
    308            // we're done! Later, we may add a concept of "cost" (i.e. number of steps) or
    309            // "quality" (how close is the tuple target type to the desired target type). Cost
    310            // is currently implicit, as compound tuples are stored deeper in the queue,
    311            // so simpler coercions will be located earlier.
    312
    313            Class tupleTargetType = tuple.getTargetType();
    314
    315            if (targetType.isAssignableFrom(tupleTargetType))
    316            {
    317                return tuple.getCoercion();
    318            }
    319
    320            // So .. this tuple doesn't get us directly to the target type.
    321            // However, it *may* get us part of the way. Each of these
    322            // represents a coercion from the source type to an intermediate type.
    323            // Now we're going to look for conversions from the intermediate type
    324            // to some other type.
    325
    326            queueIntermediates(sourceType, targetType, tuple, consideredTuples, queue);
    327        }
    328
    329        // Not found anywhere. Identify the source and target type and a (sorted) list of
    330        // all the known coercions.
    331
    332        throw new UnknownValueException(String.format("Could not find a coercion from type %s to type %s.",
    333                sourceType.getName(), targetType.getName()), buildCoercionCatalog());
    334    }
    335
    336    /**
    337     * Coercion from null is special; we match based on the target type and its not a spanning
    338     * search. In many cases, we
    339     * return a pass-thru that leaves the value as null.
    340     *
    341     * @param targetType
    342     *         desired type
    343     * @return the coercion
    344     */
    345    private Coercion searchForNullCoercion(Class targetType)
    346    {
    347        List<CoercionTuple> tuples = getTuples(Void.class, targetType);
    348
    349        for (CoercionTuple tuple : tuples)
    350        {
    351            Class tupleTargetType = tuple.getTargetType();
    352
    353            if (targetType.equals(tupleTargetType))
    354                return tuple.getCoercion();
    355        }
    356
    357        // Typical case: no match, this coercion passes the null through
    358        // as null.
    359
    360        return COERCION_NULL_TO_OBJECT;
    361    }
    362
    363    /**
    364     * Builds a string listing all the coercions configured for the type coercer, sorted
    365     * alphabetically.
    366     */
    367    @SuppressWarnings("unchecked")
    368    private AvailableValues buildCoercionCatalog()
    369    {
    370        List<CoercionTuple> masterList = CollectionFactory.newList();
    371
    372        for (List<CoercionTuple> list : sourceTypeToTuple.values())
    373        {
    374            masterList.addAll(list);
    375        }
    376
    377        return new AvailableValues("Configured coercions", masterList);
    378    }
    379
    380    /**
    381     * Seeds the pool with the initial set of coercions for the given type.
    382     */
    383    private void seedQueue(Class sourceType, Class targetType, Set<CoercionTuple> consideredTuples,
    384                           LinkedList<CoercionTuple> queue)
    385    {
    386        // Work from the source type up looking for tuples
    387
    388        for (Class c : new InheritanceSearch(sourceType))
    389        {
    390            List<CoercionTuple> tuples = getTuples(c, targetType);
    391
    392            if (tuples == null)
    393            {
    394                continue;
    395            }
    396
    397            for (CoercionTuple tuple : tuples)
    398            {
    399                queue.addLast(tuple);
    400                consideredTuples.add(tuple);
    401            }
    402
    403            // Don't pull in Object -> type coercions when doing
    404            // a search from null.
    405
    406            if (sourceType == Void.class)
    407            {
    408                return;
    409            }
    410        }
    411    }
    412
    413    /**
    414     * Creates and adds to the pool a new set of coercions based on an intermediate tuple. Adds
    415     * compound coercion tuples
    416     * to the end of the queue.
    417     *
    418     * @param sourceType
    419     *         the source type of the coercion
    420     * @param targetType
    421     *         TODO
    422     * @param intermediateTuple
    423     *         a tuple that converts from the source type to some intermediate type (that is not
    424     *         assignable to the target type)
    425     * @param consideredTuples
    426     *         set of tuples that have already been added to the pool (directly, or as a compound
    427     *         coercion)
    428     * @param queue
    429     *         the work queue of tuples
    430     */
    431    @SuppressWarnings("unchecked")
    432    private void queueIntermediates(Class sourceType, Class targetType, CoercionTuple intermediateTuple,
    433                                    Set<CoercionTuple> consideredTuples, LinkedList<CoercionTuple> queue)
    434    {
    435        Class intermediateType = intermediateTuple.getTargetType();
    436
    437        for (Class c : new InheritanceSearch(intermediateType))
    438        {
    439            for (CoercionTuple tuple : getTuples(c, targetType))
    440            {
    441                if (consideredTuples.contains(tuple))
    442                {
    443                    continue;
    444                }
    445
    446                Class newIntermediateType = tuple.getTargetType();
    447
    448                // If this tuple is for coercing from an intermediate type back towards our
    449                // initial source type, then ignore it. This should only be an optimization,
    450                // as branches that loop back towards the source type will
    451                // eventually be considered and discarded.
    452
    453                if (sourceType.isAssignableFrom(newIntermediateType))
    454                {
    455                    continue;
    456                }
    457
    458                // The intermediateTuple coercer gets from S --> I1 (an intermediate type).
    459                // The current tuple's coercer gets us from I2 --> X. where I2 is assignable
    460                // from I1 (i.e., I2 is a superclass/superinterface of I1) and X is a new
    461                // intermediate type, hopefully closer to our eventual target type.
    462
    463                Coercion compoundCoercer = new CompoundCoercion(intermediateTuple.getCoercion(), tuple.getCoercion());
    464
    465                CoercionTuple compoundTuple = new CoercionTuple(sourceType, newIntermediateType, compoundCoercer, false);
    466
    467                // So, every tuple that is added to the queue can take as input the sourceType.
    468                // The target type may be another intermediate type, or may be something
    469                // assignable to the target type, which will bring the search to a successful
    470                // conclusion.
    471
    472                queue.addLast(compoundTuple);
    473                consideredTuples.add(tuple);
    474            }
    475        }
    476    }
    477
    478    /**
    479     * Returns a non-null list of the tuples from the source type.
    480     *
    481     * @param sourceType
    482     *         used to locate tuples
    483     * @param targetType
    484     *         used to add synthetic tuples
    485     * @return non-null list of tuples
    486     */
    487    private List<CoercionTuple> getTuples(Class sourceType, Class targetType)
    488    {
    489        List<CoercionTuple> tuples = sourceTypeToTuple.get(sourceType);
    490
    491        if (tuples == null)
    492        {
    493            tuples = Collections.emptyList();
    494        }
    495
    496        // So, when we see String and an Enum type, we add an additional synthetic tuple to the end
    497        // of the real list. This is the easiest way to accomplish this is a thread-safe and class-reloading
    498        // safe way (i.e., what if the Enum is defined by a class loader that gets discarded?  Don't want to cause
    499        // memory leaks by retaining an instance). In any case, there are edge cases where we may create
    500        // the tuple unnecessarily (such as when an explicit string-to-enum coercion is part of the TypeCoercer
    501        // configuration), but on the whole, this is cheap and works.
    502
    503        if (sourceType == String.class && Enum.class.isAssignableFrom(targetType))
    504        {
    505            tuples = extend(tuples, new CoercionTuple(sourceType, targetType, new StringToEnumCoercion(targetType)));
    506        }
    507        else if (Enum.class.isAssignableFrom(sourceType) && targetType == String.class)
    508        {
    509            // TAP5-2565
    510            tuples = extend(tuples, new CoercionTuple(sourceType, targetType, COERCION_ENUM_TO_STRING));
    511        }
    512
    513        return tuples;
    514    }
    515
    516    private static <T> List<T> extend(List<T> list, T extraValue)
    517    {
    518        return F.flow(list).append(extraValue).toList();
    519    }
    520}