001/*
002 * Copyright 2006-2007 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.batch.item.support;
018
019import org.springframework.batch.item.ItemProcessor;
020import org.springframework.beans.factory.InitializingBean;
021import org.springframework.util.Assert;
022
023import java.util.List;
024
025/**
026 * Composite {@link ItemProcessor} that passes the item through a sequence of
027 * injected <code>ItemTransformer</code>s (return value of previous
028 * transformation is the entry value of the next).<br>
029 * <br>
030 * 
031 * Note the user is responsible for injecting a chain of {@link ItemProcessor}s
032 * that conforms to declared input and output types.
033 * 
034 * @author Robert Kasanicky
035 */
036public class CompositeItemProcessor<I, O> implements ItemProcessor<I, O>, InitializingBean {
037
038        private List<? extends ItemProcessor<?, ?>> delegates;
039
040        @Override
041        @SuppressWarnings("unchecked")
042        public O process(I item) throws Exception {
043                Object result = item;
044
045                for (ItemProcessor<?, ?> delegate : delegates) {
046                        if (result == null) {
047                                return null;
048                        }
049
050                        result = processItem(delegate, result);
051                }
052                return (O) result;
053        }
054    
055    /* 
056     * Helper method to work around wildcard capture compiler error: see https://docs.oracle.com/javase/tutorial/java/generics/capture.html
057     * The method process(capture#1-of ?) in the type ItemProcessor<capture#1-of ?,capture#2-of ?> is not applicable for the arguments (Object)
058     */
059    @SuppressWarnings("unchecked")
060        private <T> Object processItem(ItemProcessor<T, ?> processor, Object input) throws Exception {
061        return processor.process((T) input);
062    }
063
064        @Override
065        public void afterPropertiesSet() throws Exception {
066                Assert.notNull(delegates, "The 'delegates' may not be null");
067                Assert.notEmpty(delegates, "The 'delegates' may not be empty");
068        }
069
070        /**
071         * Establishes the {@link ItemProcessor} delegates that will work on the item to be
072         * processed.
073         * @param delegates list of {@link ItemProcessor} delegates that will work on the
074         * item.
075         */
076        public void setDelegates(List<? extends ItemProcessor<?, ?>> delegates) {
077                this.delegates = delegates;
078        }
079
080}