| 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 | |
| 17 | package org.springframework.batch.item.database; |
| 18 | |
| 19 | import java.util.HashMap; |
| 20 | import java.util.Map; |
| 21 | import java.util.concurrent.CopyOnWriteArrayList; |
| 22 | |
| 23 | import javax.persistence.EntityManager; |
| 24 | import javax.persistence.EntityManagerFactory; |
| 25 | import javax.persistence.EntityTransaction; |
| 26 | import javax.persistence.Query; |
| 27 | |
| 28 | import org.springframework.batch.item.ExecutionContext; |
| 29 | import org.springframework.batch.item.database.orm.JpaQueryProvider; |
| 30 | import org.springframework.dao.DataAccessResourceFailureException; |
| 31 | import org.springframework.util.Assert; |
| 32 | import org.springframework.util.ClassUtils; |
| 33 | |
| 34 | /** |
| 35 | * <p> |
| 36 | * {@link org.springframework.batch.item.ItemReader} for reading database |
| 37 | * records built on top of JPA. |
| 38 | * </p> |
| 39 | * |
| 40 | * <p> |
| 41 | * It executes the JPQL {@link #setQueryString(String)} to retrieve requested |
| 42 | * data. The query is executed using paged requests of a size specified in |
| 43 | * {@link #setPageSize(int)}. Additional pages are requested when needed as |
| 44 | * {@link #read()} method is called, returning an object corresponding to |
| 45 | * current position. |
| 46 | * </p> |
| 47 | * |
| 48 | * <p> |
| 49 | * The performance of the paging depends on the JPA implementation and its use |
| 50 | * of database specific features to limit the number of returned rows. |
| 51 | * </p> |
| 52 | * |
| 53 | * <p> |
| 54 | * Setting a fairly large page size and using a commit interval that matches the |
| 55 | * page size should provide better performance. |
| 56 | * </p> |
| 57 | * |
| 58 | * <p> |
| 59 | * In order to reduce the memory usage for large results the persistence context |
| 60 | * is flushed and cleared after each page is read. This causes any entities read |
| 61 | * to be detached. If you make changes to the entities and want the changes |
| 62 | * persisted then you must explicitly merge the entities. |
| 63 | * </p> |
| 64 | * |
| 65 | * <p> |
| 66 | * The reader must be configured with an |
| 67 | * {@link javax.persistence.EntityManagerFactory}. All entity access is |
| 68 | * performed within a new transaction, independent of any existing Spring |
| 69 | * managed transactions. |
| 70 | * </p> |
| 71 | * |
| 72 | * <p> |
| 73 | * The implementation is thread-safe in between calls to |
| 74 | * {@link #open(ExecutionContext)}, but remember to use |
| 75 | * <code>saveState=false</code> if used in a multi-threaded client (no restart |
| 76 | * available). |
| 77 | * </p> |
| 78 | * |
| 79 | * |
| 80 | * @author Thomas Risberg |
| 81 | * @author Dave Syer |
| 82 | * @since 2.0 |
| 83 | */ |
| 84 | public class JpaPagingItemReader<T> extends AbstractPagingItemReader<T> { |
| 85 | |
| 86 | private EntityManagerFactory entityManagerFactory; |
| 87 | |
| 88 | private EntityManager entityManager; |
| 89 | |
| 90 | private final Map<String, Object> jpaPropertyMap = new HashMap<String, Object>(); |
| 91 | |
| 92 | private String queryString; |
| 93 | |
| 94 | private JpaQueryProvider queryProvider; |
| 95 | |
| 96 | private Map<String, Object> parameterValues; |
| 97 | |
| 98 | public JpaPagingItemReader() { |
| 99 | setName(ClassUtils.getShortName(JpaPagingItemReader.class)); |
| 100 | } |
| 101 | |
| 102 | /** |
| 103 | * Create a query using an appropriate query provider (entityManager OR |
| 104 | * queryProvider). |
| 105 | */ |
| 106 | private Query createQuery() { |
| 107 | if (queryProvider == null) { |
| 108 | return entityManager.createQuery(queryString); |
| 109 | } |
| 110 | else { |
| 111 | return queryProvider.createQuery(); |
| 112 | } |
| 113 | } |
| 114 | |
| 115 | public void setEntityManagerFactory(EntityManagerFactory entityManagerFactory) { |
| 116 | this.entityManagerFactory = entityManagerFactory; |
| 117 | } |
| 118 | |
| 119 | /** |
| 120 | * The parameter values to be used for the query execution. |
| 121 | * |
| 122 | * @param parameterValues the values keyed by the parameter named used in |
| 123 | * the query string. |
| 124 | */ |
| 125 | public void setParameterValues(Map<String, Object> parameterValues) { |
| 126 | this.parameterValues = parameterValues; |
| 127 | } |
| 128 | |
| 129 | public void afterPropertiesSet() throws Exception { |
| 130 | super.afterPropertiesSet(); |
| 131 | |
| 132 | if (queryProvider == null) { |
| 133 | Assert.notNull(entityManagerFactory); |
| 134 | Assert.hasLength(queryString); |
| 135 | } |
| 136 | // making sure that the appropriate (JPA) query provider is set |
| 137 | else { |
| 138 | Assert.isTrue(queryProvider != null, "JPA query provider must be set"); |
| 139 | } |
| 140 | } |
| 141 | |
| 142 | /** |
| 143 | * @param queryString JPQL query string |
| 144 | */ |
| 145 | public void setQueryString(String queryString) { |
| 146 | this.queryString = queryString; |
| 147 | } |
| 148 | |
| 149 | /** |
| 150 | * @param queryProvider JPA query provider |
| 151 | */ |
| 152 | public void setQueryProvider(JpaQueryProvider queryProvider) { |
| 153 | this.queryProvider = queryProvider; |
| 154 | } |
| 155 | |
| 156 | @Override |
| 157 | protected void doOpen() throws Exception { |
| 158 | super.doOpen(); |
| 159 | |
| 160 | entityManager = entityManagerFactory.createEntityManager(jpaPropertyMap); |
| 161 | if (entityManager == null) { |
| 162 | throw new DataAccessResourceFailureException("Unable to obtain an EntityManager"); |
| 163 | } |
| 164 | // set entityManager to queryProvider, so it participates |
| 165 | // in JpaPagingItemReader's managed transaction |
| 166 | if (queryProvider != null) { |
| 167 | queryProvider.setEntityManager(entityManager); |
| 168 | } |
| 169 | |
| 170 | } |
| 171 | |
| 172 | @Override |
| 173 | @SuppressWarnings("unchecked") |
| 174 | protected void doReadPage() { |
| 175 | |
| 176 | EntityTransaction tx = entityManager.getTransaction(); |
| 177 | tx.begin(); |
| 178 | |
| 179 | entityManager.flush(); |
| 180 | entityManager.clear(); |
| 181 | |
| 182 | Query query = createQuery().setFirstResult(getPage() * getPageSize()).setMaxResults(getPageSize()); |
| 183 | |
| 184 | if (parameterValues != null) { |
| 185 | for (Map.Entry<String, Object> me : parameterValues.entrySet()) { |
| 186 | query.setParameter(me.getKey(), me.getValue()); |
| 187 | } |
| 188 | } |
| 189 | |
| 190 | if (results == null) { |
| 191 | results = new CopyOnWriteArrayList<T>(); |
| 192 | } |
| 193 | else { |
| 194 | results.clear(); |
| 195 | } |
| 196 | results.addAll(query.getResultList()); |
| 197 | |
| 198 | tx.commit(); |
| 199 | } |
| 200 | |
| 201 | @Override |
| 202 | protected void doJumpToPage(int itemIndex) { |
| 203 | } |
| 204 | |
| 205 | @Override |
| 206 | protected void doClose() throws Exception { |
| 207 | entityManager.close(); |
| 208 | super.doClose(); |
| 209 | } |
| 210 | |
| 211 | } |