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 */
51
52 public interface SeekableByteChannel
53 extends ByteChannel
54 {
55 /**
56 * Reads a sequence of bytes from this channel into the given buffer.
57 *
58 * <p> Bytes are read starting at this channel's current position, and
59 * then the position is updated with the number of bytes actually read.
60 * Otherwise this method behaves exactly as specified in the {@link
61 * ReadableByteChannel} interface.
62 */
63 @Override
64 int read(ByteBuffer dst) throws IOException;
65
66 /**
67 * Writes a sequence of bytes to this channel from the given buffer.
68 *
69 * <p> Bytes are written starting at this channel's current position, unless
70 * the channel is connected to an entity such as a file that is opened with
71 * the {@link java.nio.file.StandardOpenOption#APPEND APPEND} option, in
72 * which case the position is first advanced to the end. The entity to which
73 * the channel is connected is grown, if necessary, to accommodate the
74 * written bytes, and then the position is updated with the number of bytes
75 * actually written. Otherwise this method behaves exactly as specified by
76 * the {@link WritableByteChannel} interface.
77 */
78 @Override
79 int write(ByteBuffer src) throws IOException;
80
81 /**
82 * Returns this channel's position.
83 *
84 * @return This channel's position,
85 * a non-negative integer counting the number of bytes
86 * from the beginning of the entity to the current position
87 *
88 * @throws ClosedChannelException
89 * If this channel is closed
90 * @throws IOException
91 * If some other I/O error occurs
92 */
93 long position() throws IOException;
94
95 /**
96 * Sets this channel's position.
97 *
98 * <p> Setting the position to a value that is greater than the current size
99 * is legal but does not change the size of the entity. A later attempt to
100 * read bytes at such a position will immediately return an end-of-file
101 * indication. A later attempt to write bytes at such a position will cause
102 * the entity to grow to accommodate the new bytes; the values of any bytes
103 * between the previous end-of-file and the newly-written bytes are
104 * unspecified.
105 *
106 * <p> Setting the channel's position is not recommended when connected to
107 * an entity, typically a file, that is opened with the {@link
108 * java.nio.file.StandardOpenOption#APPEND APPEND} option. When opened for
109 * append, the position is first advanced to the end before writing.
110 *
111 * @param newPosition
112 * The new position, a non-negative integer counting
113 * the number of bytes from the beginning of the entity
114 *
115 * @return This channel
116 *
117 * @throws ClosedChannelException
118 * If this channel is closed
119 * @throws IllegalArgumentException
120 * If the new position is negative
121 * @throws IOException
122 * If some other I/O error occurs
123 */
124 SeekableByteChannel position(long newPosition) throws IOException;
125
126 /**
127 * Returns the current size of entity to which this channel is connected.
128 *
129 * @return The current size, measured in bytes
130 *
131 * @throws ClosedChannelException
132 * If this channel is closed
133 * @throws IOException
134 * If some other I/O error occurs
135 */
136 long size() throws IOException;
137
138 /**
139 * Truncates the entity, to which this channel is connected, to the given
140 * size.
141 *
142 * <p> If the given size is less than the current size then the entity is
143 * truncated, discarding any bytes beyond the new end. If the given size is
144 * greater than or equal to the current size then the entity is not modified.
145 * In either case, if the current position is greater than the given size
146 * then it is set to that size.
147 *
148 * <p> An implementation of this interface may prohibit truncation when
149 * connected to an entity, typically a file, opened with the {@link
150 * java.nio.file.StandardOpenOption#APPEND APPEND} option.
151 *
152 * @param size
153 * The new size, a non-negative byte count
154 *
155 * @return This channel
156 *
157 * @throws NonWritableChannelException
158 * If this channel was not opened for writing
159 * @throws ClosedChannelException
160 * If this channel is closed
161 * @throws IllegalArgumentException
162 * If the new size is negative
163 * @throws IOException
164 * If some other I/O error occurs
165 */
166 SeekableByteChannel truncate(long size) throws IOException;
167 }