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