| 1 | /* |
| 2 | * Copyright 2006-2010 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.support; |
| 17 | |
| 18 | import java.util.Map.Entry; |
| 19 | |
| 20 | import org.springframework.batch.item.ExecutionContext; |
| 21 | import org.springframework.batch.item.ItemReader; |
| 22 | import org.springframework.batch.item.ItemStream; |
| 23 | import org.springframework.batch.item.ItemStreamException; |
| 24 | import org.springframework.batch.item.ItemStreamReader; |
| 25 | import org.springframework.batch.item.ParseException; |
| 26 | import org.springframework.batch.item.PeekableItemReader; |
| 27 | import org.springframework.batch.item.UnexpectedInputException; |
| 28 | |
| 29 | /** |
| 30 | * <p> |
| 31 | * A {@link PeekableItemReader} that allows the user to peek one item ahead. |
| 32 | * Repeated calls to {@link #peek()} will return the same item, and this will be |
| 33 | * the next item returned from {@link #read()}. |
| 34 | * </p> |
| 35 | * |
| 36 | * <p> |
| 37 | * Intentionally not thread safe: it wouldn't be possible to honour the peek in |
| 38 | * multiple threads because only one of the threads that peeked would get that |
| 39 | * item in the next call to read. |
| 40 | * </p> |
| 41 | * |
| 42 | * @author Dave Syer |
| 43 | * |
| 44 | */ |
| 45 | public class SingleItemPeekableItemReader<T> implements ItemStreamReader<T>, PeekableItemReader<T> { |
| 46 | |
| 47 | private ItemReader<T> delegate; |
| 48 | |
| 49 | private T next; |
| 50 | |
| 51 | private ExecutionContext executionContext = new ExecutionContext(); |
| 52 | |
| 53 | /** |
| 54 | * The item reader to use as a delegate. Items are read from the delegate |
| 55 | * and passed to the caller in {@link #read()}. |
| 56 | * |
| 57 | * @param delegate the delegate to set |
| 58 | */ |
| 59 | public void setDelegate(ItemReader<T> delegate) { |
| 60 | this.delegate = delegate; |
| 61 | } |
| 62 | |
| 63 | /** |
| 64 | * Get the next item from the delegate (whether or not it has already been |
| 65 | * peeked at). |
| 66 | * |
| 67 | * @see ItemReader#read() |
| 68 | */ |
| 69 | public T read() throws Exception, UnexpectedInputException, ParseException { |
| 70 | if (next != null) { |
| 71 | T item = next; |
| 72 | next = null; |
| 73 | // executionContext = new ExecutionContext(); |
| 74 | return item; |
| 75 | } |
| 76 | return delegate.read(); |
| 77 | } |
| 78 | |
| 79 | /** |
| 80 | * Peek at the next item, ensuring that if the delegate is an |
| 81 | * {@link ItemStream} the state is stored for the next call to |
| 82 | * {@link #update(ExecutionContext)}. |
| 83 | * |
| 84 | * @return the next item (or null if there is none). |
| 85 | * |
| 86 | * @see PeekableItemReader#peek() |
| 87 | */ |
| 88 | public T peek() throws Exception, UnexpectedInputException, ParseException { |
| 89 | if (next == null) { |
| 90 | updateDelegate(executionContext); |
| 91 | next = delegate.read(); |
| 92 | } |
| 93 | return next; |
| 94 | } |
| 95 | |
| 96 | /** |
| 97 | * If the delegate is an {@link ItemStream}, just pass the call on, |
| 98 | * otherwise reset the peek cache. |
| 99 | * |
| 100 | * @throws ItemStreamException if there is a problem |
| 101 | * @see ItemStream#close() |
| 102 | */ |
| 103 | public void close() throws ItemStreamException { |
| 104 | next = null; |
| 105 | if (delegate instanceof ItemStream) { |
| 106 | ((ItemStream) delegate).close(); |
| 107 | } |
| 108 | executionContext = new ExecutionContext(); |
| 109 | } |
| 110 | |
| 111 | /** |
| 112 | * If the delegate is an {@link ItemStream}, just pass the call on, |
| 113 | * otherwise reset the peek cache. |
| 114 | * |
| 115 | * @param executionContext the current context |
| 116 | * @throws ItemStreamException if there is a problem |
| 117 | * @see ItemStream#open(ExecutionContext) |
| 118 | */ |
| 119 | public void open(ExecutionContext executionContext) throws ItemStreamException { |
| 120 | next = null; |
| 121 | if (delegate instanceof ItemStream) { |
| 122 | ((ItemStream) delegate).open(executionContext); |
| 123 | } |
| 124 | executionContext = new ExecutionContext(); |
| 125 | } |
| 126 | |
| 127 | /** |
| 128 | * If there is a cached peek, then retrieve the execution context state from |
| 129 | * that point. If there is no peek cached, then call directly to the |
| 130 | * delegate. |
| 131 | * |
| 132 | * @param executionContext the current context |
| 133 | * @throws ItemStreamException if there is a problem |
| 134 | * @see ItemStream#update(ExecutionContext) |
| 135 | */ |
| 136 | public void update(ExecutionContext executionContext) throws ItemStreamException { |
| 137 | if (next != null) { |
| 138 | // Get the last state from the delegate instead of using |
| 139 | // current value. |
| 140 | for (Entry<String, Object> entry : this.executionContext.entrySet()) { |
| 141 | executionContext.put(entry.getKey(), entry.getValue()); |
| 142 | } |
| 143 | return; |
| 144 | } |
| 145 | updateDelegate(executionContext); |
| 146 | } |
| 147 | |
| 148 | private void updateDelegate(ExecutionContext executionContext) { |
| 149 | if (delegate instanceof ItemStream) { |
| 150 | ((ItemStream) delegate).update(executionContext); |
| 151 | } |
| 152 | } |
| 153 | |
| 154 | } |