Java tutorial
/* * Copyright (c) 2007, 2011, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.nio.channels; import java.nio.ByteBuffer; import java.io.IOException; /** * A byte channel that maintains a current <i>position</i> and allows the * position to be changed. * * <p> A seekable byte channel is connected to an entity, typically a file, * that contains a variable-length sequence of bytes that can be read and * written. The current position can be {@link #position() <i>queried</i>} and * {@link #position(long) <i>modified</i>}. The channel also provides access to * the current <i>size</i> of the entity to which the channel is connected. The * size increases when bytes are written beyond its current size; the size * decreases when it is {@link #truncate <i>truncated</i>}. * * <p> The {@link #position(long) position} and {@link #truncate truncate} methods * which do not otherwise have a value to return are specified to return the * channel upon which they are invoked. This allows method invocations to be * chained. Implementations of this interface should specialize the return type * so that method invocations on the implementation class can be chained. * * @since 1.7 * @see java.nio.file.Files#newByteChannel */ public interface SeekableByteChannel extends ByteChannel { /** * Reads a sequence of bytes from this channel into the given buffer. * * <p> Bytes are read starting at this channel's current position, and * then the position is updated with the number of bytes actually read. * Otherwise this method behaves exactly as specified in the {@link * ReadableByteChannel} interface. */ @Override int read(ByteBuffer dst) throws IOException; /** * Writes a sequence of bytes to this channel from the given buffer. * * <p> Bytes are written starting at this channel's current position, unless * the channel is connected to an entity such as a file that is opened with * the {@link java.nio.file.StandardOpenOption#APPEND APPEND} option, in * which case the position is first advanced to the end. The entity to which * the channel is connected is grown, if necessary, to accommodate the * written bytes, and then the position is updated with the number of bytes * actually written. Otherwise this method behaves exactly as specified by * the {@link WritableByteChannel} interface. */ @Override int write(ByteBuffer src) throws IOException; /** * Returns this channel's position. * * @return This channel's position, * a non-negative integer counting the number of bytes * from the beginning of the entity to the current position * * @throws ClosedChannelException * If this channel is closed * @throws IOException * If some other I/O error occurs */ long position() throws IOException; /** * Sets this channel's position. * * <p> Setting the position to a value that is greater than the current size * is legal but does not change the size of the entity. A later attempt to * read bytes at such a position will immediately return an end-of-file * indication. A later attempt to write bytes at such a position will cause * the entity to grow to accommodate the new bytes; the values of any bytes * between the previous end-of-file and the newly-written bytes are * unspecified. * * <p> Setting the channel's position is not recommended when connected to * an entity, typically a file, that is opened with the {@link * java.nio.file.StandardOpenOption#APPEND APPEND} option. When opened for * append, the position is first advanced to the end before writing. * * @param newPosition * The new position, a non-negative integer counting * the number of bytes from the beginning of the entity * * @return This channel * * @throws ClosedChannelException * If this channel is closed * @throws IllegalArgumentException * If the new position is negative * @throws IOException * If some other I/O error occurs */ SeekableByteChannel position(long newPosition) throws IOException; /** * Returns the current size of entity to which this channel is connected. * * @return The current size, measured in bytes * * @throws ClosedChannelException * If this channel is closed * @throws IOException * If some other I/O error occurs */ long size() throws IOException; /** * Truncates the entity, to which this channel is connected, to the given * size. * * <p> If the given size is less than the current size then the entity is * truncated, discarding any bytes beyond the new end. If the given size is * greater than or equal to the current size then the entity is not modified. * In either case, if the current position is greater than the given size * then it is set to that size. * * <p> An implementation of this interface may prohibit truncation when * connected to an entity, typically a file, opened with the {@link * java.nio.file.StandardOpenOption#APPEND APPEND} option. * * @param size * The new size, a non-negative byte count * * @return This channel * * @throws NonWritableChannelException * If this channel was not opened for writing * @throws ClosedChannelException * If this channel is closed * @throws IllegalArgumentException * If the new size is negative * @throws IOException * If some other I/O error occurs */ SeekableByteChannel truncate(long size) throws IOException; }