1 /* TransformingIteratorWrapper
2 *
3 * $Id: TransformingIteratorWrapper.java 4650 2006-09-25 18:09:42Z paul_jack $
4 *
5 * Created on Mar 25, 2005
6 *
7 * Copyright (C) 2005 Internet Archive.
8 *
9 * This file is part of the Heritrix web crawler (crawler.archive.org).
10 *
11 * Heritrix is free software; you can redistribute it and/or modify
12 * it under the terms of the GNU Lesser Public License as published by
13 * the Free Software Foundation; either version 2.1 of the License, or
14 * any later version.
15 *
16 * Heritrix is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 * GNU Lesser Public License for more details.
20 *
21 * You should have received a copy of the GNU Lesser Public License
22 * along with Heritrix; if not, write to the Free Software
23 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
24 */
25 package org.archive.util.iterator;
26
27 import java.util.Iterator;
28
29 /***
30 * Superclass for Iterators which transform and/or filter results
31 * from a wrapped Iterator. Because transform() has the option of
32 * discarding an item from the inner Iterator (by returning null),
33 * this is a kind of LookaheadIterator.
34 *
35 * @author gojomo
36 */
37 public abstract class TransformingIteratorWrapper<Original,Transformed>
38 extends LookaheadIterator<Transformed> {
39 protected Iterator<Original> inner;
40
41
42 /* (non-Javadoc)
43 * @see org.archive.util.iterator.LookaheadIterator#lookahead()
44 */
45 protected boolean lookahead() {
46 assert next == null : "looking ahead when next is already loaded";
47 while(inner.hasNext()) {
48 next = transform(inner.next());
49 if(next!=null) {
50 return true;
51 }
52 }
53 noteExhausted();
54 return false;
55 }
56
57 /***
58 * Any cleanup to occur when hasNext() is about to return false
59 */
60 protected void noteExhausted() {
61 // by default, do nothing
62
63 }
64
65 /***
66 * @param object Object to transform.
67 * @return Transfomed object.
68 */
69 protected abstract Transformed transform(Original object);
70
71 }