Module java.base
Package java.nio.channels

Interface SeekableByteChannel

All Superinterfaces:
AutoCloseable, ByteChannel, Channel, Closeable, ReadableByteChannel, WritableByteChannel
All Known Implementing Classes:
FileChannel
public interface SeekableByteChannel
extends ByteChannel
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.

Since:
1.7
See Also:
Files.newByteChannel(java.nio.file.Path, java.util.Set<? extends java.nio.file.OpenOption>, java.nio.file.attribute.FileAttribute<?>...)

  • Method Summary

    Modifier and Type Method Description
    long position()
    Returns this channel's position.
    SeekableByteChannel position​(long newPosition)
    Sets this channel's position.
    int read​(ByteBuffer dst)
    Reads a sequence of bytes from this channel into the given buffer.
    long size()
    Returns the current size of entity to which this channel is connected.
    SeekableByteChannel truncate​(long size)
    Truncates the entity, to which this channel is connected, to the given size.
    int write​(ByteBuffer src)
    Writes a sequence of bytes to this channel from the given buffer.

    Methods declared in interface java.nio.channels.Channel

    close, isOpen

  • Method Details

    • read

      int read​(ByteBuffer dst) throws IOException
      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.

      Specified by:
      read in interface ReadableByteChannel
      Parameters:
      dst - The buffer into which bytes are to be transferred
      Returns:
      The number of bytes read, possibly zero, or -1 if the channel has reached end-of-stream
      Throws:
      ClosedChannelException - If this channel is closed
      AsynchronousCloseException - If another thread closes this channel while the read operation is in progress
      ClosedByInterruptException - If another thread interrupts the current thread while the read operation is in progress, thereby closing the channel and setting the current thread's interrupt status
      IOException - If some other I/O error occurs

    • write

      int write​(ByteBuffer src) 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 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.

      Specified by:
      write in interface WritableByteChannel
      Parameters:
      src - The buffer from which bytes are to be retrieved
      Returns:
      The number of bytes written, possibly zero
      Throws:
      ClosedChannelException - If this channel is closed
      AsynchronousCloseException - If another thread closes this channel while the write operation is in progress
      ClosedByInterruptException - If another thread interrupts the current thread while the write operation is in progress, thereby closing the channel and setting the current thread's interrupt status
      IOException - If some other I/O error occurs

    • position

      long position() throws IOException
      Returns this channel's position.
      Returns:
      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

      SeekableByteChannel position​(long newPosition) 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 APPEND option. When opened for append, the position is first advanced to the end before writing.

      Parameters:
      newPosition - The new position, a non-negative integer counting the number of bytes from the beginning of the entity
      Returns:
      This channel
      Throws:
      ClosedChannelException - If this channel is closed
      IllegalArgumentException - If the new position is negative
      IOException - If some other I/O error occurs

    • size

      long size() throws IOException
      Returns the current size of entity to which this channel is connected.
      Returns:
      The current size, measured in bytes
      Throws:
      ClosedChannelException - If this channel is closed
      IOException - If some other I/O error occurs

    • truncate

      SeekableByteChannel truncate​(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 APPEND option.

      Parameters:
      size - The new size, a non-negative byte count
      Returns:
      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