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 package org.apache.commons.io.input.buffer;
18
19 import java.io.IOException;
20 import java.io.InputStream;
21 import java.util.Objects;
22
23 import org.apache.commons.io.IOUtils;
24
25 /**
26 * Implements a buffered input stream, which allows to peek into the buffers first bytes. This comes in handy when
27 * manually implementing scanners, lexers, parsers, and the like.
28 */
29 public class PeekableInputStream extends CircularBufferInputStream {
30
31 /**
32 * Constructs a new instance, which filters the given input stream, and uses a reasonable default buffer size ({@link IOUtils#DEFAULT_BUFFER_SIZE}).
33 *
34 * @param inputStream The input stream, which is being buffered.
35 */
36 public PeekableInputStream(final InputStream inputStream) {
37 super(inputStream);
38 }
39
40 /**
41 * Constructs a new instance, which filters the given input stream, and uses the given buffer size.
42 *
43 * @param inputStream The input stream, which is being buffered.
44 * @param bufferSize The size of the {@link CircularByteBuffer}, which is used internally.
45 */
46 public PeekableInputStream(final InputStream inputStream, final int bufferSize) {
47 super(inputStream, bufferSize);
48 }
49
50 /**
51 * Returns whether the next bytes in the buffer are as given by {@code sourceBuffer}. This is equivalent to
52 * {@link #peek(byte[], int, int)} with {@code offset} == 0, and {@code length} == {@code sourceBuffer.length}
53 *
54 * @param sourceBuffer the buffer to compare against
55 * @return true if the next bytes are as given
56 * @throws IOException Refilling the buffer failed.
57 */
58 public boolean peek(final byte[] sourceBuffer) throws IOException {
59 Objects.requireNonNull(sourceBuffer, "sourceBuffer");
60 return peek(sourceBuffer, 0, sourceBuffer.length);
61 }
62
63 /**
64 * Returns whether the next bytes in the buffer are as given by {@code sourceBuffer}, {code offset}, and
65 * {@code length}.
66 *
67 * @param sourceBuffer the buffer to compare against
68 * @param offset the start offset
69 * @param length the length to compare
70 * @return true if the next bytes in the buffer are as given
71 * @throws IOException if there is a problem calling fillBuffer()
72 */
73 public boolean peek(final byte[] sourceBuffer, final int offset, final int length) throws IOException {
74 Objects.requireNonNull(sourceBuffer, "sourceBuffer");
75 if (sourceBuffer.length > bufferSize) {
76 throw new IllegalArgumentException("Peek request size of " + sourceBuffer.length
77 + " bytes exceeds buffer size of " + bufferSize + " bytes");
78 }
79 if (buffer.getCurrentNumberOfBytes() < sourceBuffer.length) {
80 fillBuffer();
81 }
82 return buffer.peek(sourceBuffer, offset, length);
83 }
84 }