java.nio.channels.SeekableByteChannel Maven / Gradle / Ivy
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* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
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package java.nio.channels;
import java.nio.ByteBuffer;
import java.io.IOException;
/**
* A byte channel that maintains a current position and allows the
* position to be changed.
*
* 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() queried} and
* {@link #position(long) modified}. The channel also provides access to
* the current size 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 truncated}.
*
*
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.
*
*
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.
*
*
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.
*
*
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.
*
*
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.
*
*
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.
*
*
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;
}