    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.functors;
    018
    019import java.io.Serializable;
    020import java.util.Collection;
    021import java.util.Objects;
    022
    023import org.apache.commons.collections4.Transformer;
    024
    025/**
    026 * Transformer implementation that chains the specified transformers together.
    027 * <p>
    028 * The input object is passed to the first transformer. The transformed result
    029 * is passed to the second transformer and so on.
    030 * </p>
    031 *
    032 * @param <T> the type of the input and result to the function.
    033 * @since 3.0
    034 */
    035public class ChainedTransformer<T> implements Transformer<T, T>, Serializable {
    036
    037    @SuppressWarnings("rawtypes")
    038    private static final Transformer[] EMPTY_TRANSFORMER_ARRAY = {};
    039
    040    /** Serial version UID */
    041    private static final long serialVersionUID = 3514945074733160196L;
    042
    043    /**
    044     * Create a new Transformer that calls each transformer in turn, passing the
    045     * result into the next transformer. The ordering is that of the iterator()
    046     * method on the collection.
    047     *
    048     * @param <T>  the object type
    049     * @param transformers  a collection of transformers to chain
    050     * @return the {@code chained} transformer
    051     * @throws NullPointerException if the transformers collection is null
    052     * @throws NullPointerException if any transformer in the collection is null
    053     */
    054    public static <T> Transformer<T, T> chainedTransformer(
    055            final Collection<? extends Transformer<? super T, ? extends T>> transformers) {
    056        Objects.requireNonNull(transformers, "transformers");
    057        if (transformers.isEmpty()) {
    058            return NOPTransformer.<T>nopTransformer();
    059        }
    060        // convert to array like this to guarantee iterator() ordering
    061        final Transformer<T, T>[] cmds = transformers.toArray(EMPTY_TRANSFORMER_ARRAY);
    062        FunctorUtils.validate(cmds);
    063        return new ChainedTransformer<>(false, cmds);
    064    }
    065
    066    /**
    067     * Factory method that performs validation and copies the parameter array.
    068     *
    069     * @param <T>  the object type
    070     * @param transformers  the transformers to chain, copied, no nulls
    071     * @return the {@code chained} transformer
    072     * @throws NullPointerException if the transformers array is null
    073     * @throws NullPointerException if any transformer in the array is null
    074     */
    075    public static <T> Transformer<T, T> chainedTransformer(final Transformer<? super T, ? extends T>... transformers) {
    076        FunctorUtils.validate(transformers);
    077        if (transformers.length == 0) {
    078            return NOPTransformer.<T>nopTransformer();
    079        }
    080        return new ChainedTransformer<>(transformers);
    081    }
    082
    083    /** The transformers to call in turn */
    084    private final Transformer<? super T, ? extends T>[] iTransformers;
    085
    086    /**
    087     * Hidden constructor for the use by the static factory methods.
    088     *
    089     * @param clone  if {@code true} the input argument will be cloned
    090     * @param transformers  the transformers to chain, no nulls
    091     */
    092    private ChainedTransformer(final boolean clone, final Transformer<? super T, ? extends T>[] transformers) {
    093        iTransformers = clone ? FunctorUtils.copy(transformers) : transformers;
    094    }
    095
    096    /**
    097     * Constructor that performs no validation.
    098     * Use {@code chainedTransformer} if you want that.
    099     *
    100     * @param transformers  the transformers to chain, copied, no nulls
    101     */
    102    public ChainedTransformer(final Transformer<? super T, ? extends T>... transformers) {
    103        this(true, transformers);
    104    }
    105
    106    /**
    107     * Gets the transformers.
    108     *
    109     * @return a copy of the transformers
    110     * @since 3.1
    111     */
    112    public Transformer<? super T, ? extends T>[] getTransformers() {
    113        return FunctorUtils.copy(iTransformers);
    114    }
    115
    116    /**
    117     * Transforms the input to result via each decorated transformer
    118     *
    119     * @param object  the input object passed to the first transformer
    120     * @return the transformed result
    121     */
    122    @Override
    123    public T transform(T object) {
    124        for (final Transformer<? super T, ? extends T> iTransformer : iTransformers) {
    125            object = iTransformer.apply(object);
    126        }
    127        return object;
    128    }
    129
    130}