SeekableByteChannel
public
interface
SeekableByteChannel
implements
ByteChannel
| java.nio.channels.SeekableByteChannel |
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 queried and
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 truncated.
The position and 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.
See also:
Summary
Public methods | |
|---|---|
abstract
long
|
position()
Returns this channel's position. |
abstract
SeekableByteChannel
|
position(long newPosition)
Sets this channel's position. |
abstract
int
|
read(ByteBuffer dst)
Reads a sequence of bytes from this channel into the given buffer. |
abstract
long
|
size()
Returns the current size of entity to which this channel is connected. |
abstract
SeekableByteChannel
|
truncate(long size)
Truncates the entity, to which this channel is connected, to the given size. |
abstract
int
|
write(ByteBuffer src)
Writes a sequence of bytes to this channel from the given buffer. |
Inherited methods | |
|---|---|
Public methods
position
public abstract long position ()
Returns this channel's position.
| Returns | |
|---|---|
long |
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 |
IOException |
If some other I/O error occurs |
position
public abstract SeekableByteChannel position (long newPosition)
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 APPEND option. When opened for
append, the position is first advanced to the end before writing.
| Parameters | |
|---|---|
newPosition |
long: The new position, a non-negative integer counting
the number of bytes from the beginning of the entity |
| Returns | |
|---|---|
SeekableByteChannel |
This channel |
| Throws | |
|---|---|
ClosedChannelException |
If this channel is closed |
IllegalArgumentException |
If the new position is negative |
IOException |
If some other I/O error occurs |
read
public abstract int read (ByteBuffer dst)
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 ReadableByteChannel interface.
| Parameters | |
|---|---|
dst |
ByteBuffer: The buffer into which bytes are to be transferred |
| Returns | |
|---|---|
int |
The number of bytes read, possibly zero, or -1 if the
channel has reached end-of-stream |
| Throws | |
|---|---|
IOException |
|
size
public abstract long size ()
Returns the current size of entity to which this channel is connected.
| Returns | |
|---|---|
long |
The current size, measured in bytes |
| Throws | |
|---|---|
ClosedChannelException |
If this channel is closed |
IOException |
If some other I/O error occurs |
truncate
public abstract SeekableByteChannel truncate (long size)
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 APPEND option.
| Parameters | |
|---|---|
size |
long: The new size, a non-negative byte count |
| Returns | |
|---|---|
SeekableByteChannel |
This channel |
| Throws | |
|---|---|
NonWritableChannelException |
If this channel was not opened for writing |
ClosedChannelException |
If this channel is closed |
IllegalArgumentException |
If the new size is negative |
IOException |
If some other I/O error occurs |
write
public abstract int write (ByteBuffer src)
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 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 WritableByteChannel interface.
| Parameters | |
|---|---|
src |
ByteBuffer: The buffer from which bytes are to be retrieved |
| Returns | |
|---|---|
int |
The number of bytes written, possibly zero |
| Throws | |
|---|---|
IOException |
|