| 1 | /* |
| 2 | * Copyright 2006-2007 the original author or authors. |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
| 17 | package org.springframework.batch.item.support; |
| 18 | |
| 19 | import java.util.ArrayList; |
| 20 | import java.util.Collection; |
| 21 | |
| 22 | import org.apache.commons.logging.Log; |
| 23 | import org.apache.commons.logging.LogFactory; |
| 24 | import org.springframework.batch.item.ItemReader; |
| 25 | import org.springframework.batch.item.file.mapping.FieldSetMapper; |
| 26 | |
| 27 | /** |
| 28 | * An {@link ItemReader} that delivers a list as its item, storing up objects |
| 29 | * from the injected {@link ItemReader} until they are ready to be packed out |
| 30 | * as a collection. The {@link ItemReader} should mark the beginning and end of |
| 31 | * records with the constant values in {@link FieldSetMapper} ({@link AggregateItemReader#BEGIN_RECORD} |
| 32 | * and {@link AggregateItemReader#END_RECORD}).<br/> |
| 33 | * |
| 34 | * This class is thread safe (it can be used concurrently by multiple threads) |
| 35 | * as long as the {@link ItemReader} is also thread safe. |
| 36 | * |
| 37 | * @author Dave Syer |
| 38 | * |
| 39 | */ |
| 40 | public class AggregateItemReader extends DelegatingItemReader { |
| 41 | |
| 42 | private static final Log log = LogFactory |
| 43 | .getLog(AggregateItemReader.class); |
| 44 | |
| 45 | /** |
| 46 | * Marker for the end of a multi-object record. |
| 47 | */ |
| 48 | public static final Object END_RECORD = new Object(); |
| 49 | |
| 50 | /** |
| 51 | * Marker for the beginning of a multi-object record. |
| 52 | */ |
| 53 | public static final Object BEGIN_RECORD = new Object(); |
| 54 | |
| 55 | /** |
| 56 | * Get the next list of records. |
| 57 | * @throws Exception |
| 58 | * |
| 59 | * @see org.springframework.batch.item.ItemReader#read() |
| 60 | */ |
| 61 | public Object read() throws Exception { |
| 62 | ResultHolder holder = new ResultHolder(); |
| 63 | |
| 64 | while (process(super.read(), holder)) { |
| 65 | continue; |
| 66 | } |
| 67 | |
| 68 | if (!holder.exhausted) { |
| 69 | return holder.records; |
| 70 | } else { |
| 71 | return null; |
| 72 | } |
| 73 | } |
| 74 | |
| 75 | private boolean process(Object value, ResultHolder holder) { |
| 76 | // finish processing if we hit the end of file |
| 77 | if (value == null) { |
| 78 | log.debug("Exhausted ItemReader"); |
| 79 | holder.exhausted = true; |
| 80 | return false; |
| 81 | } |
| 82 | |
| 83 | // start a new collection |
| 84 | if (value == AggregateItemReader.BEGIN_RECORD) { |
| 85 | log.debug("Start of new record detected"); |
| 86 | return true; |
| 87 | } |
| 88 | |
| 89 | // mark we are finished with current collection |
| 90 | if (value == AggregateItemReader.END_RECORD) { |
| 91 | log.debug("End of record detected"); |
| 92 | return false; |
| 93 | } |
| 94 | |
| 95 | // add a simple record to the current collection |
| 96 | log.debug("Mapping: " + value); |
| 97 | holder.records.add(value); |
| 98 | return true; |
| 99 | } |
| 100 | |
| 101 | /** |
| 102 | * Private class for temporary state management while item is being |
| 103 | * collected. |
| 104 | * |
| 105 | * @author Dave Syer |
| 106 | * |
| 107 | */ |
| 108 | private static class ResultHolder { |
| 109 | Collection records = new ArrayList(); |
| 110 | boolean exhausted = false; |
| 111 | } |
| 112 | |
| 113 | } |