    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      https://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.collections4;
    018
    019import java.util.Collection;
    020import java.util.LinkedHashMap;
    021import java.util.Map;
    022import java.util.Objects;
    023
    024import org.apache.commons.collections4.functors.ChainedTransformer;
    025import org.apache.commons.collections4.functors.CloneTransformer;
    026import org.apache.commons.collections4.functors.ClosureTransformer;
    027import org.apache.commons.collections4.functors.ConstantTransformer;
    028import org.apache.commons.collections4.functors.EqualPredicate;
    029import org.apache.commons.collections4.functors.ExceptionTransformer;
    030import org.apache.commons.collections4.functors.FactoryTransformer;
    031import org.apache.commons.collections4.functors.IfTransformer;
    032import org.apache.commons.collections4.functors.InstantiateTransformer;
    033import org.apache.commons.collections4.functors.InvokerTransformer;
    034import org.apache.commons.collections4.functors.MapTransformer;
    035import org.apache.commons.collections4.functors.NOPTransformer;
    036import org.apache.commons.collections4.functors.PredicateTransformer;
    037import org.apache.commons.collections4.functors.StringValueTransformer;
    038import org.apache.commons.collections4.functors.SwitchTransformer;
    039
    040/**
    041 * {@code TransformerUtils} provides reference implementations and
    042 * utilities for the Transformer functor interface. The supplied transformers are:
    043 * <ul>
    044 * <li>Invoker - returns the result of a method call on the input object</li>
    045 * <li>Clone - returns a clone of the input object</li>
    046 * <li>Constant - always returns the same object</li>
    047 * <li>Closure - performs a Closure and returns the input object</li>
    048 * <li>Predicate - returns the result of the predicate as a Boolean</li>
    049 * <li>Factory - returns a new object from a factory</li>
    050 * <li>Chained - chains two or more transformers together</li>
    051 * <li>If - calls one transformer or another based on a predicate</li>
    052 * <li>Switch - calls one transformer based on one or more predicates</li>
    053 * <li>SwitchMap - calls one transformer looked up from a Map</li>
    054 * <li>Instantiate - the Class input object is instantiated</li>
    055 * <li>Map - returns an object from a supplied Map</li>
    056 * <li>Null - always returns null</li>
    057 * <li>NOP - returns the input object, which should be immutable</li>
    058 * <li>Exception - always throws an exception</li>
    059 * <li>StringValue - returns a {@link String} representation of the input object</li>
    060 * </ul>
    061 * <p>
    062 * Since v4.1 only transformers which are considered to be safe are
    063 * Serializable. Transformers considered to be unsafe for serialization are:
    064 * </p>
    065 * <ul>
    066 * <li>Invoker</li>
    067 * <li>Clone</li>
    068 * <li>Instantiate</li>
    069 * </ul>
    070 *
    071 * @since 3.0
    072 */
    073public class TransformerUtils {
    074
    075    /**
    076     * Creates a Transformer that calls a Closure each time the transformer is used.
    077     * The transformer returns the input object.
    078     *
    079     * @param <T>  the input/output type
    080     * @param closure  The closure to run each time in the transformer, not null
    081     * @return The transformer
    082     * @throws NullPointerException if the closure is null
    083     * @see ClosureTransformer
    084     */
    085    public static <T> Transformer<T, T> asTransformer(final Closure<? super T> closure) {
    086        return ClosureTransformer.closureTransformer(closure);
    087    }
    088
    089    /**
    090     * Creates a Transformer that calls a Factory each time the transformer is used.
    091     * The transformer will return the value returned by the factory.
    092     *
    093     * @param <I>  the input type
    094     * @param <O>  the output type
    095     * @param factory  The factory to run each time in the transformer, not null
    096     * @return The transformer
    097     * @throws NullPointerException if the factory is null
    098     * @see FactoryTransformer
    099     */
    100    public static <I, O> Transformer<I, O> asTransformer(final Factory<? extends O> factory) {
    101        return FactoryTransformer.factoryTransformer(factory);
    102    }
    103
    104    /**
    105     * Creates a Transformer that calls a Predicate each time the transformer is used.
    106     * The transformer will return either {@link Boolean#TRUE} or {@link Boolean#FALSE}.
    107     *
    108     * @param <T>  the input type
    109     * @param predicate  The predicate to run each time in the transformer, not null
    110     * @return The transformer
    111     * @throws NullPointerException if the predicate is null
    112     * @see PredicateTransformer
    113     */
    114    public static <T> Transformer<T, Boolean> asTransformer(final Predicate<? super T> predicate) {
    115        return PredicateTransformer.predicateTransformer(predicate);
    116    }
    117
    118    /**
    119     * Create a new Transformer that calls each transformer in turn, passing the
    120     * result into the next transformer. The ordering is that of the iterator()
    121     * method on the collection.
    122     *
    123     * @param <T>  the input/output type
    124     * @param transformers  A collection of transformers to chain
    125     * @return The transformer
    126     * @throws NullPointerException if the transformers collection or any of the transformers is null
    127     * @see ChainedTransformer
    128     */
    129    public static <T> Transformer<T, T> chainedTransformer(
    130            final Collection<? extends Transformer<? super T, ? extends T>> transformers) {
    131        return ChainedTransformer.chainedTransformer(transformers);
    132    }
    133
    134    /**
    135     * Create a new Transformer that calls each transformer in turn, passing the
    136     * result into the next transformer.
    137     *
    138     * @param <T>  the input/output type
    139     * @param transformers  An array of transformers to chain
    140     * @return The transformer
    141     * @throws NullPointerException if the transformers array or any of the transformers is null
    142     * @see ChainedTransformer
    143     */
    144    public static <T> Transformer<T, T> chainedTransformer(
    145            final Transformer<? super T, ? extends T>... transformers) {
    146        return ChainedTransformer.chainedTransformer(transformers);
    147    }
    148
    149    /**
    150     * Gets a transformer that returns a clone of the input object.
    151     * The input object will be cloned using one of these techniques (in order):
    152     * <ul>
    153     * <li>public clone method</li>
    154     * <li>public copy constructor</li>
    155     * <li>serialization clone</li>
    156     * </ul>
    157     *
    158     * @param <T>  the input/output type
    159     * @return The transformer
    160     * @see CloneTransformer
    161     */
    162    public static <T> Transformer<T, T> cloneTransformer() {
    163        return CloneTransformer.cloneTransformer();
    164    }
    165
    166    /**
    167     * Creates a Transformer that will return the same object each time the
    168     * transformer is used.
    169     *
    170     * @param <I>  the input type
    171     * @param <O>  the output type
    172     * @param constantToReturn  The constant object to return each time in the transformer
    173     * @return The transformer.
    174     * @see ConstantTransformer
    175     */
    176    public static <I, O> Transformer<I, O> constantTransformer(final O constantToReturn) {
    177        return ConstantTransformer.constantTransformer(constantToReturn);
    178    }
    179
    180    /**
    181     * Gets a transformer that always throws an exception.
    182     * This could be useful during testing as a placeholder.
    183     *
    184     * @param <I>  the input type
    185     * @param <O>  the output type
    186     * @return The transformer
    187     * @see ExceptionTransformer
    188     */
    189    public static <I, O> Transformer<I, O> exceptionTransformer() {
    190        return ExceptionTransformer.exceptionTransformer();
    191    }
    192
    193    /**
    194     * Create a new Transformer that calls one of two transformers depending
    195     * on the specified predicate.
    196     *
    197     * @param <I>  the input type
    198     * @param <O>  the output type
    199     * @param predicate  The predicate to switch on
    200     * @param trueTransformer  The transformer called if the predicate is true
    201     * @param falseTransformer  The transformer called if the predicate is false
    202     * @return The transformer
    203     * @throws NullPointerException if either the predicate or transformer is null
    204     * @see IfTransformer
    205     * @since 4.1
    206     */
    207    public static <I, O> Transformer<I, O> ifTransformer(final Predicate<? super I> predicate,
    208                                                         final Transformer<? super I, ? extends O> trueTransformer,
    209                                                         final Transformer<? super I, ? extends O> falseTransformer) {
    210        return IfTransformer.ifTransformer(predicate, trueTransformer, falseTransformer);
    211    }
    212
    213    /**
    214     * Create a new Transformer that calls the transformer if the predicate is true,
    215     * otherwise the input object is returned unchanged.
    216     *
    217     * @param <T>  the input / output type
    218     * @param predicate  The predicate to switch on
    219     * @param trueTransformer  The transformer called if the predicate is true
    220     * @return The transformer
    221     * @throws NullPointerException if either the predicate or transformer is null
    222     * @see IfTransformer
    223     * @since 4.1
    224     */
    225    public static <T> Transformer<T, T> ifTransformer(final Predicate<? super T> predicate,
    226                                                      final Transformer<? super T, ? extends T> trueTransformer) {
    227        return IfTransformer.ifTransformer(predicate, trueTransformer);
    228    }
    229
    230    /**
    231     * Gets a Transformer that expects an input Class object that it will instantiate.
    232     *
    233     * @param <T>  the output type
    234     * @return The transformer
    235     * @see InstantiateTransformer
    236     */
    237    public static <T> Transformer<Class<? extends T>, T> instantiateTransformer() {
    238        return InstantiateTransformer.instantiateTransformer();
    239    }
    240
    241    /**
    242     * Creates a Transformer that expects an input Class object that it will
    243     * instantiate. The constructor used is determined by the arguments specified
    244     * to this method.
    245     *
    246     * @param <T>  the output type
    247     * @param paramTypes  parameter types for the constructor, can be null
    248     * @param args  The arguments to pass to the constructor, can be null
    249     * @return The transformer
    250     * @throws IllegalArgumentException if the paramTypes and args don't match
    251     * @see InstantiateTransformer
    252     */
    253    public static <T> Transformer<Class<? extends T>, T> instantiateTransformer(
    254            final Class<?>[] paramTypes, final Object[] args) {
    255        return InstantiateTransformer.instantiateTransformer(paramTypes, args);
    256    }
    257
    258    /**
    259     * Gets a Transformer that invokes a method on the input object.
    260     * The method must have no parameters. If the input object is {@code null},
    261     * {@code null} is returned.
    262     *
    263     * <p>
    264     * For example, {@code TransformerUtils.invokerTransformer("getName");}
    265     * will call the {@code getName} method on the input object to
    266     * determine the transformer result.
    267     * </p>
    268     *
    269     * @param <I>  the input type
    270     * @param <O>  the output type
    271     * @param methodName  The method name to call on the input object, may not be null
    272     * @return The transformer
    273     * @throws NullPointerException if the methodName is null.
    274     * @see InvokerTransformer
    275     */
    276    public static <I, O> Transformer<I, O> invokerTransformer(final String methodName) {
    277        return InvokerTransformer.invokerTransformer(methodName, null, null);
    278    }
    279
    280    /**
    281     * Gets a Transformer that invokes a method on the input object.
    282     * The method parameters are specified. If the input object is {@code null},
    283     * {@code null} is returned.
    284     *
    285     * @param <I>  the input type
    286     * @param <O>  the output type
    287     * @param methodName  The name of the method
    288     * @param paramTypes  The parameter types
    289     * @param args  The arguments
    290     * @return The transformer
    291     * @throws NullPointerException if the method name is null
    292     * @throws IllegalArgumentException if the paramTypes and args don't match
    293     * @see InvokerTransformer
    294     */
    295    public static <I, O> Transformer<I, O> invokerTransformer(final String methodName, final Class<?>[] paramTypes,
    296                                                              final Object[] args) {
    297        return InvokerTransformer.invokerTransformer(methodName, paramTypes, args);
    298    }
    299
    300    /**
    301     * Creates a Transformer that uses the passed in Map to transform the input
    302     * object (as a simple lookup).
    303     *
    304     * @param <I>  the input type
    305     * @param <O>  the output type
    306     * @param map  The map to use to transform the objects
    307     * @return The transformer, or {@link ConstantTransformer#nullTransformer()} if the
    308     *   {@code map} is {@code null}
    309     * @see MapTransformer
    310     */
    311    public static <I, O> Transformer<I, O> mapTransformer(final Map<? super I, ? extends O> map) {
    312        return MapTransformer.mapTransformer(map);
    313    }
    314
    315    /**
    316     * Gets a transformer that returns the input object.
    317     * The input object should be immutable to maintain the
    318     * contract of Transformer (although this is not checked).
    319     *
    320     * @param <T>  the input/output type
    321     * @return The transformer
    322     * @see NOPTransformer
    323     */
    324    public static <T> Transformer<T, T> nopTransformer() {
    325        return NOPTransformer.nopTransformer();
    326    }
    327
    328    /**
    329     * Gets a transformer that always returns null.
    330     *
    331     * @param <I>  the input type
    332     * @param <O>  the output type
    333     * @return The transformer
    334     * @see ConstantTransformer
    335     */
    336    public static <I, O> Transformer<I, O> nullTransformer() {
    337        return ConstantTransformer.nullTransformer();
    338    }
    339
    340    /**
    341     * Gets a transformer that returns a {@link String}
    342     * representation of the input object. This is achieved via the
    343     * {@code toString} method, {@code null} returns 'null'.
    344     *
    345     * @param <T>  the input type
    346     * @return The transformer
    347     * @see StringValueTransformer
    348     */
    349    public static <T> Transformer<T, String> stringValueTransformer() {
    350        return StringValueTransformer.stringValueTransformer();
    351    }
    352
    353    /**
    354     * Create a new Transformer that uses the input object as a key to find the
    355     * transformer to call.
    356     * <p>
    357     * The Map consists of object keys and Transformer values. A transformer
    358     * is called if the input object equals the key. If there is no match, the
    359     * default transformer is called. The default transformer is set in the map
    360     * using a null key. If no default is set, null will be returned in a default case.
    361     * </p>
    362     *
    363     * @param <I>  the input type
    364     * @param <O>  the output type
    365     * @param objectsAndTransformers  A map of objects to transformers
    366     * @return The transformer
    367     * @throws NullPointerException if the map is null
    368     * @throws NullPointerException if any transformer in the map is null
    369     * @see SwitchTransformer
    370     */
    371    @SuppressWarnings("unchecked")
    372    public static <I, O> Transformer<I, O> switchMapTransformer(
    373            final Map<I, Transformer<I, O>> objectsAndTransformers) {
    374
    375        Objects.requireNonNull(objectsAndTransformers, "objectsAndTransformers");
    376        // copy so the caller's map is not mutated
    377        final Map<I, Transformer<I, O>> objects = new LinkedHashMap<>(objectsAndTransformers);
    378        final Transformer<? super I, ? extends O> def = objects.remove(null);
    379        final int size = objects.size();
    380        final Transformer<? super I, ? extends O>[] trs = new Transformer[size];
    381        final Predicate<I>[] preds = new Predicate[size];
    382        int i = 0;
    383        for (final Map.Entry<I, Transformer<I, O>> entry : objects.entrySet()) {
    384            preds[i] = EqualPredicate.<I>equalPredicate(entry.getKey());
    385            trs[i++] = entry.getValue();
    386        }
    387        return switchTransformer(preds, trs, def);
    388    }
    389
    390    /**
    391     * Create a new Transformer that calls one of the transformers depending
    392     * on the predicates.
    393     * <p>
    394     * The Map consists of Predicate keys and Transformer values. A transformer
    395     * is called if its matching predicate returns true. Each predicate is evaluated
    396     * until one returns true. If no predicates evaluate to true, the default
    397     * transformer is called. The default transformer is set in the map with a
    398     * null key. If no default transformer is set, null will be returned in a default
    399     * case. The ordering is that of the iterator() method on the entryset collection
    400     * of the map.
    401     * </p>
    402     *
    403     * @param <I>  the input type
    404     * @param <O>  the output type
    405     * @param predicatesAndTransformers  A map of predicates to transformers
    406     * @return The transformer
    407     * @throws NullPointerException if the map is null
    408     * @throws NullPointerException if any transformer in the map is null
    409     * @throws ClassCastException  if the map elements are of the wrong type
    410     * @see SwitchTransformer
    411     */
    412    public static <I, O> Transformer<I, O> switchTransformer(
    413            final Map<Predicate<I>, Transformer<I, O>> predicatesAndTransformers) {
    414        return SwitchTransformer.switchTransformer(predicatesAndTransformers);
    415    }
    416
    417    /**
    418     * Create a new Transformer that calls one of two transformers depending
    419     * on the specified predicate.
    420     *
    421     * @param <I>  the input type
    422     * @param <O>  the output type
    423     * @param predicate  The predicate to switch on
    424     * @param trueTransformer  The transformer called if the predicate is true
    425     * @param falseTransformer  The transformer called if the predicate is false
    426     * @return The transformer
    427     * @throws NullPointerException if either the predicate or transformer is null
    428     * @see SwitchTransformer
    429     * @deprecated as of 4.1, use {@link #ifTransformer(Predicate, Transformer, Transformer)}
    430     */
    431    @SuppressWarnings("unchecked")
    432    @Deprecated
    433    public static <I, O> Transformer<I, O> switchTransformer(final Predicate<? super I> predicate,
    434            final Transformer<? super I, ? extends O> trueTransformer,
    435            final Transformer<? super I, ? extends O> falseTransformer) {
    436        return SwitchTransformer.switchTransformer(new Predicate[] { predicate },
    437                                                   new Transformer[] { trueTransformer }, falseTransformer);
    438    }
    439
    440    /**
    441     * Create a new Transformer that calls one of the transformers depending
    442     * on the predicates. The transformer at array location 0 is called if the
    443     * predicate at array location 0 returned true. Each predicate is evaluated
    444     * until one returns true. If no predicates evaluate to true, null is returned.
    445     *
    446     * @param <I>  the input type
    447     * @param <O>  the output type
    448     * @param predicates  An array of predicates to check
    449     * @param transformers  An array of transformers to call
    450     * @return The transformer
    451     * @throws NullPointerException if either array is null
    452     * @throws NullPointerException if any element in the arrays is null
    453     * @throws IllegalArgumentException if the arrays have different sizes
    454     * @see SwitchTransformer
    455     */
    456    public static <I, O> Transformer<I, O> switchTransformer(final Predicate<? super I>[] predicates,
    457            final Transformer<? super I, ? extends O>[] transformers) {
    458        return SwitchTransformer.switchTransformer(predicates, transformers, null);
    459    }
    460
    461    /**
    462     * Create a new Transformer that calls one of the transformers depending
    463     * on the predicates. The transformer at array location 0 is called if the
    464     * predicate at array location 0 returned true. Each predicate is evaluated
    465     * until one returns true. If no predicates evaluate to true, the default
    466     * transformer is called. If the default transformer is null, null is returned.
    467     *
    468     * @param <I>  the input type
    469     * @param <O>  the output type
    470     * @param predicates  An array of predicates to check
    471     * @param transformers  An array of transformers to call
    472     * @param defaultTransformer  The default to call if no predicate matches, null means return null
    473     * @return The transformer
    474     * @throws NullPointerException if either array is null
    475     * @throws NullPointerException if any element in the arrays is null
    476     * @throws IllegalArgumentException if the arrays have different sizes
    477     * @see SwitchTransformer
    478     */
    479    public static <I, O> Transformer<I, O> switchTransformer(final Predicate<? super I>[] predicates,
    480            final Transformer<? super I, ? extends O>[] transformers,
    481            final Transformer<? super I, ? extends O> defaultTransformer) {
    482        return SwitchTransformer.switchTransformer(predicates, transformers, defaultTransformer);
    483    }
    484
    485    /**
    486     * This class is not normally instantiated.
    487     */
    488    private TransformerUtils() {
    489        // empty
    490    }
    491
    492}