| 1 | package org.springframework.batch.item.data; |
| 2 | |
| 3 | import java.util.Iterator; |
| 4 | |
| 5 | import org.springframework.batch.item.ItemReader; |
| 6 | import org.springframework.batch.item.ItemStreamReader; |
| 7 | import org.springframework.batch.item.support.AbstractItemCountingItemStreamItemReader; |
| 8 | |
| 9 | /** |
| 10 | * A base class that handles basic reading logic based on the paginated |
| 11 | * semantics of Spring Data's paginated facilities. It also handles the |
| 12 | * semantics required for restartability based on those facilities. |
| 13 | * |
| 14 | * @author Michael Minella |
| 15 | * @since 2.2 |
| 16 | * @param <T> Type of item to be read |
| 17 | */ |
| 18 | public abstract class AbstractPaginatedDataItemReader<T> extends |
| 19 | AbstractItemCountingItemStreamItemReader<T> { |
| 20 | |
| 21 | protected volatile int page = 0; |
| 22 | |
| 23 | protected int pageSize = 10; |
| 24 | |
| 25 | protected Iterator<T> results; |
| 26 | |
| 27 | private Object lock = new Object(); |
| 28 | |
| 29 | /** |
| 30 | * The number of items to be read with each page. |
| 31 | * |
| 32 | * @param pageSize the number of items |
| 33 | */ |
| 34 | public void setPageSize(int pageSize) { |
| 35 | this.pageSize = pageSize; |
| 36 | } |
| 37 | |
| 38 | @Override |
| 39 | protected T doRead() throws Exception { |
| 40 | |
| 41 | synchronized (lock) { |
| 42 | if(results == null || !results.hasNext()) { |
| 43 | |
| 44 | results = doPageRead(); |
| 45 | |
| 46 | page ++; |
| 47 | |
| 48 | if(results == null || !results.hasNext()) { |
| 49 | return null; |
| 50 | } |
| 51 | } |
| 52 | |
| 53 | |
| 54 | if(results.hasNext()) { |
| 55 | return results.next(); |
| 56 | } |
| 57 | else { |
| 58 | return null; |
| 59 | } |
| 60 | } |
| 61 | } |
| 62 | |
| 63 | /** |
| 64 | * Method this {@link ItemStreamReader} delegates to |
| 65 | * for the actual work of reading a page. Each time |
| 66 | * this method is called, the resulting {@link Iterator} |
| 67 | * should contain the items read within the next page. |
| 68 | * <br/><br/> |
| 69 | * If the {@link Iterator} is empty or null when it is |
| 70 | * returned, this {@link ItemReader} will assume that the |
| 71 | * input has been exhausted. |
| 72 | * |
| 73 | * @return an {@link Iterator} containing the items within a page. |
| 74 | */ |
| 75 | protected abstract Iterator<T> doPageRead(); |
| 76 | |
| 77 | @Override |
| 78 | protected void doOpen() throws Exception { |
| 79 | } |
| 80 | |
| 81 | @Override |
| 82 | protected void doClose() throws Exception { |
| 83 | } |
| 84 | |
| 85 | @Override |
| 86 | protected void jumpToItem(int itemLastIndex) throws Exception { |
| 87 | synchronized (lock) { |
| 88 | page = itemLastIndex / pageSize; |
| 89 | int current = itemLastIndex % pageSize; |
| 90 | |
| 91 | Iterator<T> initialPage = doPageRead(); |
| 92 | |
| 93 | for(; current >= 0; current--) { |
| 94 | initialPage.next(); |
| 95 | } |
| 96 | } |
| 97 | } |
| 98 | } |