| 1 | /* |
| 2 | * Copyright 2006-2008 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 | package org.springframework.batch.item.database; |
| 17 | |
| 18 | import java.util.List; |
| 19 | |
| 20 | import org.apache.commons.logging.Log; |
| 21 | import org.apache.commons.logging.LogFactory; |
| 22 | import org.springframework.batch.item.support.AbstractItemCountingItemStreamItemReader; |
| 23 | import org.springframework.beans.factory.InitializingBean; |
| 24 | import org.springframework.util.Assert; |
| 25 | import org.springframework.util.ClassUtils; |
| 26 | |
| 27 | /** |
| 28 | * Abstract {@link org.springframework.batch.item.ItemReader} for to extend when |
| 29 | * reading database records in a paging fashion. |
| 30 | * |
| 31 | * <p> |
| 32 | * Implementations should execute queries using paged requests of a size |
| 33 | * specified in {@link #setPageSize(int)}. Additional pages are requested when |
| 34 | * needed as {@link #read()} method is called, returning an object corresponding |
| 35 | * to current position. |
| 36 | * </p> |
| 37 | * |
| 38 | * @author Thomas Risberg |
| 39 | * @author Dave Syer |
| 40 | * @since 2.0 |
| 41 | */ |
| 42 | public abstract class AbstractPagingItemReader<T> extends AbstractItemCountingItemStreamItemReader<T> implements |
| 43 | InitializingBean { |
| 44 | |
| 45 | protected Log logger = LogFactory.getLog(getClass()); |
| 46 | |
| 47 | private volatile boolean initialized = false; |
| 48 | |
| 49 | private int pageSize = 10; |
| 50 | |
| 51 | private volatile int current = 0; |
| 52 | |
| 53 | private volatile int page = 0; |
| 54 | |
| 55 | protected volatile List<T> results; |
| 56 | |
| 57 | private Object lock = new Object(); |
| 58 | |
| 59 | public AbstractPagingItemReader() { |
| 60 | setName(ClassUtils.getShortName(AbstractPagingItemReader.class)); |
| 61 | } |
| 62 | |
| 63 | /** |
| 64 | * The current page number. |
| 65 | * @return the current page |
| 66 | */ |
| 67 | public int getPage() { |
| 68 | return page; |
| 69 | } |
| 70 | |
| 71 | /** |
| 72 | * The page size configured for this reader. |
| 73 | * @return the page size |
| 74 | */ |
| 75 | public int getPageSize() { |
| 76 | return pageSize; |
| 77 | } |
| 78 | |
| 79 | /** |
| 80 | * The number of rows to retrieve at a time. |
| 81 | * |
| 82 | * @param pageSize the number of rows to fetch per page |
| 83 | */ |
| 84 | public void setPageSize(int pageSize) { |
| 85 | this.pageSize = pageSize; |
| 86 | } |
| 87 | |
| 88 | /** |
| 89 | * Check mandatory properties. |
| 90 | * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet() |
| 91 | */ |
| 92 | public void afterPropertiesSet() throws Exception { |
| 93 | Assert.isTrue(pageSize > 0, "pageSize must be greater than zero"); |
| 94 | } |
| 95 | |
| 96 | @Override |
| 97 | protected T doRead() throws Exception { |
| 98 | |
| 99 | synchronized (lock) { |
| 100 | |
| 101 | if (results == null || current >= pageSize) { |
| 102 | |
| 103 | if (logger.isDebugEnabled()) { |
| 104 | logger.debug("Reading page " + getPage()); |
| 105 | } |
| 106 | |
| 107 | doReadPage(); |
| 108 | page++; |
| 109 | if (current >= pageSize) { |
| 110 | current = 0; |
| 111 | } |
| 112 | |
| 113 | } |
| 114 | |
| 115 | int next = current++; |
| 116 | if (next < results.size()) { |
| 117 | return results.get(next); |
| 118 | } |
| 119 | else { |
| 120 | return null; |
| 121 | } |
| 122 | |
| 123 | } |
| 124 | |
| 125 | } |
| 126 | |
| 127 | abstract protected void doReadPage(); |
| 128 | |
| 129 | @Override |
| 130 | protected void doOpen() throws Exception { |
| 131 | |
| 132 | Assert.state(!initialized, "Cannot open an already opened ItemReader, call close first"); |
| 133 | initialized = true; |
| 134 | |
| 135 | } |
| 136 | |
| 137 | @Override |
| 138 | protected void doClose() throws Exception { |
| 139 | |
| 140 | synchronized (lock) { |
| 141 | initialized = false; |
| 142 | current = 0; |
| 143 | page = 0; |
| 144 | results = null; |
| 145 | } |
| 146 | |
| 147 | } |
| 148 | |
| 149 | @Override |
| 150 | protected void jumpToItem(int itemIndex) throws Exception { |
| 151 | |
| 152 | synchronized (lock) { |
| 153 | page = itemIndex / pageSize; |
| 154 | current = itemIndex % pageSize; |
| 155 | } |
| 156 | |
| 157 | doJumpToPage(itemIndex); |
| 158 | |
| 159 | if (logger.isDebugEnabled()) { |
| 160 | logger.debug("Jumping to page " + getPage() + " and index " + current); |
| 161 | } |
| 162 | |
| 163 | } |
| 164 | |
| 165 | abstract protected void doJumpToPage(int itemIndex); |
| 166 | |
| 167 | } |