1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18 package org.apache.commons.io;
19
20 import java.util.Iterator;
21 import java.util.Objects;
22 import java.util.stream.Stream;
23
24 /**
25 * Wraps and presents a {@link Stream} as a {@link AutoCloseable} {@link Iterator} resource that automatically closes itself when reaching the end of stream.
26 *
27 * <h2>Warning</h2>
28 * <p>
29 * In order to close the stream, the call site MUST either close the stream it allocated OR call this iterator until the end.
30 * </p>
31 *
32 * @param <E> The {@link Stream} and {@link Iterator} type.
33 * @since 2.15.0
34 */
35 public final class StreamIterator<E> implements Iterator<E>, AutoCloseable {
36
37 /**
38 * Wraps and presents a stream as a closable resource that automatically closes itself when reaching the end of stream.
39 * <p>
40 * <b>Warning</b>
41 * </p>
42 * <p>
43 * In order to close the stream, the call site MUST either close the stream it allocated OR call this iterator until the end.
44 * </p>
45 *
46 * @param <T> The stream and iterator type.
47 * @param stream The stream iterate.
48 * @return A new iterator.
49 */
50 public static <T> StreamIterator<T> iterator(final Stream<T> stream) {
51 return new StreamIterator<>(stream);
52 }
53
54 /**
55 * The given stream's Iterator.
56 */
57 private final Iterator<E> iterator;
58
59 /**
60 * The given stream.
61 */
62 private final Stream<E> stream;
63
64 /**
65 * Whether {@link #close()} has been called.
66 */
67 private boolean closed;
68
69 private StreamIterator(final Stream<E> stream) {
70 this.stream = Objects.requireNonNull(stream, "stream");
71 this.iterator = stream.iterator();
72 }
73
74 /**
75 * Closes the underlying stream.
76 */
77 @Override
78 public void close() {
79 closed = true;
80 stream.close();
81 }
82
83 @Override
84 public boolean hasNext() {
85 if (closed) {
86 // Calling Iterator#hasNext() on a closed java.nio.file.FileTreeIterator causes an IllegalStateException.
87 return false;
88 }
89 final boolean hasNext = iterator.hasNext();
90 if (!hasNext) {
91 close();
92 }
93 return hasNext;
94 }
95
96 @Override
97 public E next() {
98 final E next = iterator.next();
99 if (next == null) {
100 close();
101 }
102 return next;
103 }
104
105 }