    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 *      http://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.Map;
    021import java.util.Objects;
    022
    023import org.apache.commons.collections4.functors.ChainedClosure;
    024import org.apache.commons.collections4.functors.EqualPredicate;
    025import org.apache.commons.collections4.functors.ExceptionClosure;
    026import org.apache.commons.collections4.functors.ForClosure;
    027import org.apache.commons.collections4.functors.IfClosure;
    028import org.apache.commons.collections4.functors.InvokerTransformer;
    029import org.apache.commons.collections4.functors.NOPClosure;
    030import org.apache.commons.collections4.functors.SwitchClosure;
    031import org.apache.commons.collections4.functors.TransformerClosure;
    032import org.apache.commons.collections4.functors.WhileClosure;
    033
    034/**
    035 * {@code ClosureUtils} provides reference implementations and utilities
    036 * for the Closure functor interface. The supplied closures are:
    037 * <ul>
    038 * <li>Invoker - invokes a method on the input object
    039 * <li>For - repeatedly calls a closure for a fixed number of times
    040 * <li>While - repeatedly calls a closure while a predicate is true
    041 * <li>Chained - chains two or more closures together
    042 * <li>If - calls one closure or another based on a predicate
    043 * <li>Switch - calls one closure based on one or more predicates
    044 * <li>SwitchMap - calls one closure looked up from a Map
    045 * <li>Transformer - wraps a Transformer as a Closure
    046 * <li>NOP - does nothing
    047 * <li>Exception - always throws an exception
    048 * </ul>
    049 * <p>
    050 * Since v4.1 only closures which are considered to be safe are
    051 * Serializable. Closures considered to be unsafe for serialization are:
    052 * </p>
    053 * <ul>
    054 * <li>Invoker
    055 * <li>For
    056 * <li>While
    057 * </ul>
    058 *
    059 * @since 3.0
    060 */
    061public class ClosureUtils {
    062
    063    /**
    064     * Creates a Closure that calls a Transformer each time it is called.
    065     * The transformer will be called using the closure's input object.
    066     * The transformer's result will be ignored.
    067     *
    068     * @see org.apache.commons.collections4.functors.TransformerClosure
    069     * @param <E>  the type that the closure acts on
    070     * @param transformer  the transformer to run each time in the closure, null means nop
    071     * @return the closure
    072     */
    073    public static <E> Closure<E> asClosure(final Transformer<? super E, ?> transformer) {
    074        return TransformerClosure.transformerClosure(transformer);
    075    }
    076
    077    /**
    078     * Create a new Closure that calls each closure in turn, passing the
    079     * result into the next closure.
    080     *
    081     * @see org.apache.commons.collections4.functors.ChainedClosure
    082     * @param <E>  the type that the closure acts on
    083     * @param closures  an array of closures to chain
    084     * @return the {@code chained} closure
    085     * @throws NullPointerException if the closures array is null
    086     * @throws NullPointerException if any closure in the array is null
    087     */
    088    public static <E> Closure<E> chainedClosure(final Closure<? super E>... closures) {
    089        return ChainedClosure.chainedClosure(closures);
    090    }
    091
    092    /**
    093     * Create a new Closure that calls each closure in turn, passing the
    094     * result into the next closure. The ordering is that of the iterator()
    095     * method on the collection.
    096     *
    097     * @see org.apache.commons.collections4.functors.ChainedClosure
    098     * @param <E>  the type that the closure acts on
    099     * @param closures  a collection of closures to chain
    100     * @return the {@code chained} closure
    101     * @throws NullPointerException if the closures collection is null
    102     * @throws NullPointerException if any closure in the collection is null
    103     */
    104    public static <E> Closure<E> chainedClosure(final Collection<? extends Closure<? super E>> closures) {
    105        return ChainedClosure.chainedClosure(closures);
    106    }
    107
    108    /**
    109     * Creates a Closure that will call the closure once and then repeatedly
    110     * until the predicate returns false.
    111     *
    112     * @see org.apache.commons.collections4.functors.WhileClosure
    113     * @param <E>  the type that the closure acts on
    114     * @param closure  the closure to call repeatedly, not null
    115     * @param predicate  the predicate to use as an end of loop test, not null
    116     * @return the {@code do-while} closure
    117     * @throws NullPointerException if either argument is null
    118     */
    119    public static <E> Closure<E> doWhileClosure(final Closure<? super E> closure,
    120                                                final Predicate<? super E> predicate) {
    121        return WhileClosure.<E>whileClosure(predicate, closure, true);
    122    }
    123
    124    /**
    125     * Gets a Closure that always throws an exception.
    126     * This could be useful during testing as a placeholder.
    127     *
    128     * @param <E>  the type that the closure acts on
    129     * @return the closure
    130     * @see ExceptionClosure
    131     */
    132    public static <E> Closure<E> exceptionClosure() {
    133        return ExceptionClosure.<E>exceptionClosure();
    134    }
    135
    136    /**
    137     * Creates a Closure that will call the closure {@code count} times.
    138     * <p>
    139     * A null closure or zero count returns the {@code NOPClosure}.
    140     *
    141     * @see org.apache.commons.collections4.functors.ForClosure
    142     * @param <E>  the type that the closure acts on
    143     * @param count  the number of times to loop
    144     * @param closure  the closure to call repeatedly
    145     * @return the {@code for} closure
    146     */
    147    public static <E> Closure<E> forClosure(final int count, final Closure<? super E> closure) {
    148        return ForClosure.forClosure(count, closure);
    149    }
    150
    151    /**
    152     * Create a new Closure that calls another closure based on the
    153     * result of the specified predicate.
    154     *
    155     * @see org.apache.commons.collections4.functors.IfClosure
    156     * @param <E>  the type that the closure acts on
    157     * @param predicate  the validating predicate
    158     * @param trueClosure  the closure called if the predicate is true
    159     * @return the {@code if} closure
    160     * @throws NullPointerException if the predicate or closure is null
    161     * @since 3.2
    162     */
    163    public static <E> Closure<E> ifClosure(final Predicate<? super E> predicate,
    164                                           final Closure<? super E> trueClosure) {
    165        return IfClosure.<E>ifClosure(predicate, trueClosure);
    166    }
    167
    168    /**
    169     * Create a new Closure that calls one of two closures depending
    170     * on the specified predicate.
    171     *
    172     * @see org.apache.commons.collections4.functors.IfClosure
    173     * @param <E>  the type that the closure acts on
    174     * @param predicate  the predicate to switch on
    175     * @param trueClosure  the closure called if the predicate is true
    176     * @param falseClosure  the closure called if the predicate is false
    177     * @return the {@code switch} closure
    178     * @throws NullPointerException if the predicate or either closure is null
    179     */
    180    public static <E> Closure<E> ifClosure(final Predicate<? super E> predicate,
    181                                           final Closure<? super E> trueClosure,
    182                                           final Closure<? super E> falseClosure) {
    183        return IfClosure.<E>ifClosure(predicate, trueClosure, falseClosure);
    184    }
    185
    186    /**
    187     * Creates a Closure that will invoke a specific method on the closure's
    188     * input object by reflection.
    189     *
    190     * @see org.apache.commons.collections4.functors.InvokerTransformer
    191     * @see org.apache.commons.collections4.functors.TransformerClosure
    192     * @param <E>  the type that the closure acts on
    193     * @param methodName  the name of the method
    194     * @return the {@code invoker} closure
    195     * @throws NullPointerException if the method name is null
    196     */
    197    public static <E> Closure<E> invokerClosure(final String methodName) {
    198        // reuse transformer as it has caching - this is lazy really, should have inner class here
    199        return asClosure(InvokerTransformer.<E, Object>invokerTransformer(methodName));
    200    }
    201
    202    /**
    203     * Creates a Closure that will invoke a specific method on the closure's
    204     * input object by reflection.
    205     *
    206     * @see org.apache.commons.collections4.functors.InvokerTransformer
    207     * @see org.apache.commons.collections4.functors.TransformerClosure
    208     * @param <E>  the type that the closure acts on
    209     * @param methodName  the name of the method
    210     * @param paramTypes  the parameter types
    211     * @param args  the arguments
    212     * @return the {@code invoker} closure
    213     * @throws NullPointerException if the method name is null
    214     * @throws IllegalArgumentException if the paramTypes and args don't match
    215     */
    216    public static <E> Closure<E> invokerClosure(final String methodName, final Class<?>[] paramTypes,
    217                                                final Object[] args) {
    218        // reuse transformer as it has caching - this is lazy really, should have inner class here
    219        return asClosure(InvokerTransformer.<E, Object>invokerTransformer(methodName, paramTypes, args));
    220    }
    221
    222    /**
    223     * Gets a Closure that will do nothing.
    224     * This could be useful during testing as a placeholder.
    225     *
    226     * @see org.apache.commons.collections4.functors.NOPClosure
    227     * @param <E>  the type that the closure acts on
    228     * @return the closure
    229     */
    230    public static <E> Closure<E> nopClosure() {
    231        return NOPClosure.<E>nopClosure();
    232    }
    233
    234    /**
    235     * Create a new Closure that calls one of the closures depending
    236     * on the predicates.
    237     * <p>
    238     * The Map consists of Predicate keys and Closure values. A closure
    239     * is called if its matching predicate returns true. Each predicate is evaluated
    240     * until one returns true. If no predicates evaluate to true, the default
    241     * closure is called. The default closure is set in the map with a
    242     * null key. The ordering is that of the iterator() method on the entryset
    243     * collection of the map.
    244     * </p>
    245     *
    246     * @see org.apache.commons.collections4.functors.SwitchClosure
    247     * @param <E>  the type that the closure acts on
    248     * @param predicatesAndClosures  a map of predicates to closures
    249     * @return the {@code switch} closure
    250     * @throws NullPointerException if the map is null
    251     * @throws NullPointerException if any closure in the map is null
    252     * @throws ClassCastException  if the map elements are of the wrong type
    253     */
    254    public static <E> Closure<E> switchClosure(final Map<Predicate<E>, Closure<E>> predicatesAndClosures) {
    255        return SwitchClosure.switchClosure(predicatesAndClosures);
    256    }
    257
    258    /**
    259     * Create a new Closure that calls one of the closures depending
    260     * on the predicates.
    261     * <p>
    262     * The closure at array location 0 is called if the predicate at array
    263     * location 0 returned true. Each predicate is evaluated
    264     * until one returns true.
    265     * </p>
    266     *
    267     * @see org.apache.commons.collections4.functors.SwitchClosure
    268     * @param <E>  the type that the closure acts on
    269     * @param predicates  an array of predicates to check, not null
    270     * @param closures  an array of closures to call, not null
    271     * @return the {@code switch} closure
    272     * @throws NullPointerException if either array is null
    273     * @throws NullPointerException if any element in the arrays is null
    274     * @throws IllegalArgumentException if the arrays have different sizes
    275     */
    276    public static <E> Closure<E> switchClosure(final Predicate<? super E>[] predicates,
    277                                               final Closure<? super E>[] closures) {
    278        return SwitchClosure.<E>switchClosure(predicates, closures, null);
    279    }
    280
    281    /**
    282     * Create a new Closure that calls one of the closures depending
    283     * on the predicates.
    284     * <p>
    285     * The closure at array location 0 is called if the predicate at array
    286     * location 0 returned true. Each predicate is evaluated
    287     * until one returns true. If no predicates evaluate to true, the default
    288     * closure is called.
    289     * </p>
    290     *
    291     * @see org.apache.commons.collections4.functors.SwitchClosure
    292     * @param <E>  the type that the closure acts on
    293     * @param predicates  an array of predicates to check, not null
    294     * @param closures  an array of closures to call, not null
    295     * @param defaultClosure  the default to call if no predicate matches
    296     * @return the {@code switch} closure
    297     * @throws NullPointerException if either array is null
    298     * @throws NullPointerException if any element in the arrays is null
    299     * @throws IllegalArgumentException if the arrays are different sizes
    300     */
    301    public static <E> Closure<E> switchClosure(final Predicate<? super E>[] predicates,
    302                                               final Closure<? super E>[] closures,
    303                                               final Closure<? super E> defaultClosure) {
    304        return SwitchClosure.<E>switchClosure(predicates, closures, defaultClosure);
    305    }
    306
    307    /**
    308     * Create a new Closure that uses the input object as a key to find the
    309     * closure to call.
    310     * <p>
    311     * The Map consists of object keys and Closure values. A closure
    312     * is called if the input object equals the key. If there is no match, the
    313     * default closure is called. The default closure is set in the map
    314     * using a null key.
    315     * </p>
    316     *
    317     * @see org.apache.commons.collections4.functors.SwitchClosure
    318     * @param <E>  the type that the closure acts on
    319     * @param objectsAndClosures  a map of objects to closures
    320     * @return the closure
    321     * @throws NullPointerException if the map is null
    322     * @throws NullPointerException if any closure in the map is null
    323     */
    324    @SuppressWarnings("unchecked")
    325    public static <E> Closure<E> switchMapClosure(final Map<? extends E, Closure<E>> objectsAndClosures) {
    326        Objects.requireNonNull(objectsAndClosures, "objectsAndClosures");
    327        final Closure<? super E> def = objectsAndClosures.remove(null);
    328        final int size = objectsAndClosures.size();
    329        final Closure<? super E>[] trs = new Closure[size];
    330        final Predicate<E>[] preds = new Predicate[size];
    331        int i = 0;
    332        for (final Map.Entry<? extends E, Closure<E>> entry : objectsAndClosures.entrySet()) {
    333            preds[i] = EqualPredicate.<E>equalPredicate(entry.getKey());
    334            trs[i] = entry.getValue();
    335            i++;
    336        }
    337        return ClosureUtils.<E>switchClosure(preds, trs, def);
    338    }
    339
    340    /**
    341     * Creates a Closure that will call the closure repeatedly until the
    342     * predicate returns false.
    343     *
    344     * @see org.apache.commons.collections4.functors.WhileClosure
    345     * @param <E>  the type that the closure acts on
    346     * @param predicate  the predicate to use as an end of loop test, not null
    347     * @param closure  the closure to call repeatedly, not null
    348     * @return the {@code while} closure
    349     * @throws NullPointerException if either argument is null
    350     */
    351    public static <E> Closure<E> whileClosure(final Predicate<? super E> predicate, final Closure<? super E> closure) {
    352        return WhileClosure.<E>whileClosure(predicate, closure, false);
    353    }
    354
    355    /**
    356     * Don't allow instances.
    357     */
    358    private ClosureUtils() {
    359        // empty
    360    }
    361
    362}