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