1/*
2 * Copyright (c) 2007, 2011, 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
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23 * questions.
24 */
25
26package java.nio.channels;
27
28import java.nio.ByteBuffer;
29import 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.Files#newByteChannel
51 */
52
53public 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.
71     * The entity to which
72     * the channel is connected is grown, if necessary, to accommodate the
73     * written bytes, and then the position is updated with the number of bytes
74     * actually written. Otherwise this method behaves exactly as specified by
75     * the {@link WritableByteChannel} interface.
76     */
77    @Override
78    int write(ByteBuffer src) throws IOException;
79
80    /**
81     * Returns this channel's position.
82     *
83     * @return  This channel's position,
84     *          a non-negative integer counting the number of bytes
85     *          from the beginning of the entity to the current position
86     *
87     * @throws  ClosedChannelException
88     *          If this channel is closed
89     * @throws  IOException
90     *          If some other I/O error occurs
91     */
92    long position() throws IOException;
93
94    /**
95     * Sets this channel's position.
96     *
97     * <p> Setting the position to a value that is greater than the current size
98     * is legal but does not change the size of the entity.  A later attempt to
99     * read bytes at such a position will immediately return an end-of-file
100     * indication.  A later attempt to write bytes at such a position will cause
101     * the entity to grow to accommodate the new bytes; the values of any bytes
102     * between the previous end-of-file and the newly-written bytes are
103     * unspecified.
104     *
105     * @param  newPosition
106     *         The new position, a non-negative integer counting
107     *         the number of bytes from the beginning of the entity
108     *
109     * @return  This channel
110     *
111     * @throws  ClosedChannelException
112     *          If this channel is closed
113     * @throws  IllegalArgumentException
114     *          If the new position is negative
115     * @throws  IOException
116     *          If some other I/O error occurs
117     */
118    SeekableByteChannel position(long newPosition) throws IOException;
119
120    /**
121     * Returns the current size of entity to which this channel is connected.
122     *
123     * @return  The current size, measured in bytes
124     *
125     * @throws  ClosedChannelException
126     *          If this channel is closed
127     * @throws  IOException
128     *          If some other I/O error occurs
129     */
130    long size() throws IOException;
131
132    /**
133     * Truncates the entity, to which this channel is connected, to the given
134     * size.
135     *
136     * <p> If the given size is less than the current size then the entity is
137     * truncated, discarding any bytes beyond the new end. If the given size is
138     * greater than or equal to the current size then the entity is not modified.
139     * In either case, if the current position is greater than the given size
140     * then it is set to that size.
141     *
142     * @param  size
143     *         The new size, a non-negative byte count
144     *
145     * @return  This channel
146     *
147     * @throws  NonWritableChannelException
148     *          If this channel was not opened for writing
149     * @throws  ClosedChannelException
150     *          If this channel is closed
151     * @throws  IllegalArgumentException
152     *          If the new size is negative
153     * @throws  IOException
154     *          If some other I/O error occurs
155     */
156    SeekableByteChannel truncate(long size) throws IOException;
157}
158