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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.sample.domain.multiline;
18  
19  import java.util.ArrayList;
20  import java.util.List;
21  
22  import org.apache.commons.logging.Log;
23  import org.apache.commons.logging.LogFactory;
24  import org.springframework.batch.item.ItemReader;
25  
26  /**
27   * An {@link ItemReader} that delivers a list as its item, storing up objects
28   * from the injected {@link ItemReader} until they are ready to be packed out as
29   * a collection. This class must be used as a wrapper for a custom
30   * {@link ItemReader} that can identify the record boundaries. The custom reader
31   * should mark the beginning and end of records by returning an
32   * {@link AggregateItem} which responds true to its query methods
33   * <code>is*()</code>.<br/><br/>
34   * 
35   * This class is thread safe (it can be used concurrently by multiple threads)
36   * as long as the {@link ItemReader} is also thread safe.
37   * 
38   * @see AggregateItem#isHeader()
39   * @see AggregateItem#isFooter()
40   * 
41   * @author Dave Syer
42   * 
43   */
44  public class AggregateItemReader<T> implements ItemReader<List<T>> {
45  
46  	private static final Log log = LogFactory.getLog(AggregateItemReader.class);
47  
48  	private ItemReader<AggregateItem<T>> itemReader;
49  
50  	/**
51  	 * Get the next list of records.
52  	 * @throws Exception
53  	 * 
54  	 * @see org.springframework.batch.item.ItemReader#read()
55  	 */
56  	public List<T> read() throws Exception {
57  		ResultHolder holder = new ResultHolder();
58  
59  		while (process(itemReader.read(), holder)) {
60  			continue;
61  		}
62  
63  		if (!holder.exhausted) {
64  			return holder.records;
65  		}
66  		else {
67  			return null;
68  		}
69  	}
70  
71  	private boolean process(AggregateItem<T> value, ResultHolder holder) {
72  		// finish processing if we hit the end of file
73  		if (value == null) {
74  			log.debug("Exhausted ItemReader");
75  			holder.exhausted = true;
76  			return false;
77  		}
78  
79  		// start a new collection
80  		if (value.isHeader()) {
81  			log.debug("Start of new record detected");
82  			return true;
83  		}
84  
85  		// mark we are finished with current collection
86  		if (value.isFooter()) {
87  			log.debug("End of record detected");
88  			return false;
89  		}
90  
91  		// add a simple record to the current collection
92  		log.debug("Mapping: " + value);
93  		holder.records.add(value.getItem());
94  		return true;
95  	}
96  
97  	public void setItemReader(ItemReader<AggregateItem<T>> itemReader) {
98  		this.itemReader = itemReader;
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 class ResultHolder {
109 		List<T> records = new ArrayList<T>();
110 
111 		boolean exhausted = false;
112 	}
113 
114 }