1 /*
2 * Copyright (c) 2007, 2009, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.nio.channels;
27
28 import java.nio.ByteBuffer;
29 import java.io.IOException;
30
31 /**
32 * A byte channel that maintains a current <i>position</i> and allows the
33 * position to be changed.
34 *
35 * <p> A seekable byte channel is connected to an entity, typically a file,
36 * that contains a variable-length sequence of bytes that can be read and
37 * written. The current position can be {@link #position() <i>queried</i>} and
38 * {@link #position(long) <i>modified</i>}. The channel also provides access to
39 * the current <i>size</i> of the entity to which the channel is connected. The
40 * size increases when bytes are written beyond its current size; the size
41 * decreases when it is {@link #truncate <i>truncated</i>}.
42 *
43 * <p> The {@link #position(long) position} and {@link #truncate truncate} methods
44 * which do not otherwise have a value to return are specified to return the
45 * channel upon which they are invoked. This allows method invocations to be
46 * chained. Implementations of this interface should specialize the return type
47 * so that method invocations on the implementation class can be chained.
48 *
49 * @since 1.7
50 * @see java.nio.file.Path#newByteChannel
51 */
52
53 public interface SeekableByteChannel
54 extends ByteChannel
55 {
56 /**
57 * Reads a sequence of bytes from this channel into the given buffer.
58 *
59 * <p> Bytes are read starting at this channel's current position, and
60 * then the position is updated with the number of bytes actually read.
61 * Otherwise this method behaves exactly as specified in the {@link
62 * ReadableByteChannel} interface.
63 */
64 @Override
65 int read(ByteBuffer dst) throws IOException;
66
67 /**
68 * Writes a sequence of bytes to this channel from the given buffer.
69 *
70 * <p> Bytes are written starting at this channel's current position, unless
71 * the channel is connected to an entity such as a file that is opened with
72 * the {@link java.nio.file.StandardOpenOption#APPEND APPEND} option, in
73 * which case the position is first advanced to the end. The entity to which
74 * the channel is connected is grown, if necessary, to accommodate the
75 * written bytes, and then the position is updated with the number of bytes
76 * actually written. Otherwise this method behaves exactly as specified by
77 * the {@link WritableByteChannel} interface.
78 */
79 @Override
80 int write(ByteBuffer src) throws IOException;
81
82 /**
83 * Returns this channel's position.
84 *
85 * @return This channel's position,
86 * a non-negative integer counting the number of bytes
87 * from the beginning of the entity to the current position
88 *
89 * @throws ClosedChannelException
90 * If this channel is closed
91 * @throws IOException
92 * If some other I/O error occurs
93 */
94 long position() throws IOException;
95
96 /**
97 * Sets this channel's position.
98 *
99 * <p> Setting the position to a value that is greater than the current size
100 * is legal but does not change the size of the entity. A later attempt to
101 * read bytes at such a position will immediately return an end-of-file
102 * indication. A later attempt to write bytes at such a position will cause
103 * the entity to grow to accommodate the new bytes; the values of any bytes
104 * between the previous end-of-file and the newly-written bytes are
105 * unspecified.
106 *
107 * <p> Setting the channel's position is not recommended when connected to
108 * an entity, typically a file, that is opened with the {@link
109 * java.nio.file.StandardOpenOption#APPEND APPEND} option. When opened for
110 * append, the position is first advanced to the end before writing.
111 *
112 * @param newPosition
113 * The new position, a non-negative integer counting
114 * the number of bytes from the beginning of the entity
115 *
116 * @return This channel
117 *
118 * @throws ClosedChannelException
119 * If this channel is closed
120 * @throws IllegalArgumentException
121 * If the new position is negative
122 * @throws IOException
123 * If some other I/O error occurs
124 */
125 SeekableByteChannel position(long newPosition) throws IOException;
126
127 /**
128 * Returns the current size of entity to which this channel is connected.
129 *
130 * @return The current size, measured in bytes
131 *
132 * @throws ClosedChannelException
133 * If this channel is closed
134 * @throws IOException
135 * If some other I/O error occurs
136 */
137 long size() throws IOException;
138
139 /**
140 * Truncates the entity, to which this channel is connected, to the given
141 * size.
142 *
143 * <p> If the given size is less than the current size then the entity is
144 * truncated, discarding any bytes beyond the new end. If the given size is
145 * greater than or equal to the current size then the entity is not modified.
146 * In either case, if the current position is greater than the given size
147 * then it is set to that size.
148 *
149 * <p> An implementation of this interface may prohibit truncation when
150 * connected to an entity, typically a file, opened with the {@link
151 * java.nio.file.StandardOpenOption#APPEND APPEND} option.
152 *
153 * @param size
154 * The new size, a non-negative byte count
155 *
156 * @return This channel
157 *
158 * @throws NonWritableChannelException
159 * If this channel was not opened for writing
160 * @throws ClosedChannelException
161 * If this channel is closed
162 * @throws IllegalArgumentException
163 * If the new size is negative
164 * @throws IOException
165 * If some other I/O error occurs
166 */
167 SeekableByteChannel truncate(long size) throws IOException;
168 }