| 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 org.springframework.batch.item.ExecutionContext; |
| 20 | import org.springframework.batch.item.ItemReader; |
| 21 | import org.springframework.batch.item.ItemStreamException; |
| 22 | import org.springframework.batch.item.ItemStreamReader; |
| 23 | import org.springframework.batch.item.ParseException; |
| 24 | import org.springframework.batch.item.UnexpectedInputException; |
| 25 | import org.springframework.batch.item.util.ExecutionContextUserSupport; |
| 26 | import org.springframework.util.Assert; |
| 27 | |
| 28 | /** |
| 29 | * Abstract superclass for {@link ItemReader}s that supports restart by storing |
| 30 | * item count in the {@link ExecutionContext} (therefore requires item ordering |
| 31 | * to be preserved between runs). |
| 32 | * |
| 33 | * Subclasses are inherently *not* thread-safe. |
| 34 | * |
| 35 | * @author Robert Kasanicky |
| 36 | */ |
| 37 | public abstract class AbstractItemCountingItemStreamItemReader<T> implements ItemStreamReader<T> { |
| 38 | |
| 39 | private static final String READ_COUNT = "read.count"; |
| 40 | |
| 41 | private static final String READ_COUNT_MAX = "read.count.max"; |
| 42 | |
| 43 | private int currentItemCount = 0; |
| 44 | |
| 45 | private int maxItemCount = Integer.MAX_VALUE; |
| 46 | |
| 47 | private ExecutionContextUserSupport ecSupport = new ExecutionContextUserSupport(); |
| 48 | |
| 49 | private boolean saveState = true; |
| 50 | |
| 51 | /** |
| 52 | * Read next item from input. |
| 53 | * |
| 54 | * @return item |
| 55 | * @throws Exception |
| 56 | */ |
| 57 | protected abstract T doRead() throws Exception; |
| 58 | |
| 59 | /** |
| 60 | * Open resources necessary to start reading input. |
| 61 | */ |
| 62 | protected abstract void doOpen() throws Exception; |
| 63 | |
| 64 | /** |
| 65 | * Close the resources opened in {@link #doOpen()}. |
| 66 | */ |
| 67 | protected abstract void doClose() throws Exception; |
| 68 | |
| 69 | /** |
| 70 | * Move to the given item index. Subclasses should override this method if |
| 71 | * there is a more efficient way of moving to given index than re-reading |
| 72 | * the input using {@link #doRead()}. |
| 73 | */ |
| 74 | protected void jumpToItem(int itemIndex) throws Exception { |
| 75 | for (int i = 0; i < itemIndex; i++) { |
| 76 | read(); |
| 77 | } |
| 78 | } |
| 79 | |
| 80 | public final T read() throws Exception, UnexpectedInputException, ParseException { |
| 81 | if (currentItemCount >= maxItemCount) { |
| 82 | return null; |
| 83 | } |
| 84 | currentItemCount++; |
| 85 | return doRead(); |
| 86 | } |
| 87 | |
| 88 | protected int getCurrentItemCount() { |
| 89 | return currentItemCount; |
| 90 | } |
| 91 | |
| 92 | /** |
| 93 | * The index of the item to start reading from. If the |
| 94 | * {@link ExecutionContext} contains a key <code>[name].read.count</code> |
| 95 | * (where <code>[name]</code> is the name of this component) the value from |
| 96 | * the {@link ExecutionContext} will be used in preference. |
| 97 | * |
| 98 | * @see #setName(String) |
| 99 | * |
| 100 | * @param count the value of the current item count |
| 101 | */ |
| 102 | public void setCurrentItemCount(int count) { |
| 103 | this.currentItemCount = count; |
| 104 | } |
| 105 | |
| 106 | /** |
| 107 | * The maximum index of the items to be read. If the |
| 108 | * {@link ExecutionContext} contains a key |
| 109 | * <code>[name].read.count.max</code> (where <code>[name]</code> is the name |
| 110 | * of this component) the value from the {@link ExecutionContext} will be |
| 111 | * used in preference. |
| 112 | * |
| 113 | * @see #setName(String) |
| 114 | * |
| 115 | * @param count the value of the maximum item count |
| 116 | */ |
| 117 | public void setMaxItemCount(int count) { |
| 118 | this.maxItemCount = count; |
| 119 | } |
| 120 | |
| 121 | public void close() throws ItemStreamException { |
| 122 | currentItemCount = 0; |
| 123 | try { |
| 124 | doClose(); |
| 125 | } |
| 126 | catch (Exception e) { |
| 127 | throw new ItemStreamException("Error while closing item reader", e); |
| 128 | } |
| 129 | } |
| 130 | |
| 131 | public void open(ExecutionContext executionContext) throws ItemStreamException { |
| 132 | |
| 133 | try { |
| 134 | doOpen(); |
| 135 | } |
| 136 | catch (Exception e) { |
| 137 | throw new ItemStreamException("Failed to initialize the reader", e); |
| 138 | } |
| 139 | if (!isSaveState()) { |
| 140 | return; |
| 141 | } |
| 142 | |
| 143 | if (executionContext.containsKey(ecSupport.getKey(READ_COUNT_MAX))) { |
| 144 | maxItemCount = executionContext.getInt(ecSupport.getKey(READ_COUNT_MAX)); |
| 145 | } |
| 146 | |
| 147 | if (executionContext.containsKey(ecSupport.getKey(READ_COUNT))) { |
| 148 | int itemCount = executionContext.getInt(ecSupport.getKey(READ_COUNT)); |
| 149 | |
| 150 | if (itemCount < maxItemCount) { |
| 151 | try { |
| 152 | jumpToItem(itemCount); |
| 153 | } |
| 154 | catch (Exception e) { |
| 155 | throw new ItemStreamException("Could not move to stored position on restart", e); |
| 156 | } |
| 157 | } |
| 158 | currentItemCount = itemCount; |
| 159 | |
| 160 | } |
| 161 | |
| 162 | } |
| 163 | |
| 164 | public void update(ExecutionContext executionContext) throws ItemStreamException { |
| 165 | if (saveState) { |
| 166 | Assert.notNull(executionContext, "ExecutionContext must not be null"); |
| 167 | executionContext.putInt(ecSupport.getKey(READ_COUNT), currentItemCount); |
| 168 | if (maxItemCount < Integer.MAX_VALUE) { |
| 169 | executionContext.putInt(ecSupport.getKey(READ_COUNT_MAX), maxItemCount); |
| 170 | } |
| 171 | } |
| 172 | |
| 173 | } |
| 174 | |
| 175 | protected ExecutionContextUserSupport getExecutionContextUserSupport() { |
| 176 | return ecSupport; |
| 177 | } |
| 178 | |
| 179 | /** |
| 180 | * The name of the component which will be used as a stem for keys in the |
| 181 | * {@link ExecutionContext}. Subclasses should provide a default value, e.g. |
| 182 | * the short form of the class name. |
| 183 | * |
| 184 | * @param name the name for the component |
| 185 | */ |
| 186 | public void setName(String name) { |
| 187 | ecSupport.setName(name); |
| 188 | } |
| 189 | |
| 190 | /** |
| 191 | * Set the flag that determines whether to save internal data for |
| 192 | * {@link ExecutionContext}. Only switch this to false if you don't want to |
| 193 | * save any state from this stream, and you don't need it to be restartable. |
| 194 | * Always set it to false if the reader is being used in a concurrent |
| 195 | * environment. |
| 196 | * |
| 197 | * @param saveState flag value (default true). |
| 198 | */ |
| 199 | public void setSaveState(boolean saveState) { |
| 200 | this.saveState = saveState; |
| 201 | } |
| 202 | |
| 203 | /** |
| 204 | * The flag that determines whether to save internal state for restarts. |
| 205 | * @return true if the flag was set |
| 206 | */ |
| 207 | public boolean isSaveState() { |
| 208 | return saveState; |
| 209 | } |
| 210 | |
| 211 | } |