Writing Files - Beginning Java - page 465

The channel interfaces all extend a common interface, java.nio.channels.Channel , which declares two
methods:
• The close() method, which closes a channel
• The isOpen() method, which tests the state of the channel, returning true if it is open and false
otherwise
Because the channel interfaces all extend the AutoCloseable interface, all channel objects can be closed
automatically if you create them in a try block with resources. The methods that each channel interface in
the hierarchy declares are as follows:
ReadableByteChannel interface:
• int read(ByteBuffer input) : Reads bytes from a channel into the input buffer and returns
the number of bytes read, or −1 if the end of the stream is reached.
WritableByteChannel interface:
• int write(ByteBuffer output) : Writes bytes from the output buffer to the channel and returns
the number of bytes written.
• ByteChannel interface: This interface just inherits methods from the ReadableByteChannel and
WritableByteChannel interfaces. No additional methods are declared.
SeekableByteChannel interface:
• long position() : Returns the current position for the channel that corresponds to the current file
position.
• SeekableByteChannel position(long new)) : Sets the channel's position and thus the position
in the file to new .
• int read(ByteBuffer buf) : Reads bytes from the channel into buf and returns the number of
bytes read, or −1 if the channel has reached the end of the stream.
• int write(ByteBuffer buf) : Writes the contents of buf to the channel and returns the number
of bytes written.
• SeekableByteChannel truncate(long size) : Truncates the file to which the channel is con-
nected to size bytes and returns a reference to the channel to permit chaining method calls. If
size is greater than the current size then the file is not modified.
• long size() : Returns the number of bytes in the file to which the channel is attached.
ScatteringByteChannel interface:
• int read(ByteBuffer[] inputs) : Reads bytes from the channel into the array of buffers in-
puts and returns the number of bytes read or −1 if the end of the stream is reached.
• int read(ByteBuffer[] inputs, int offset, int length) : Reads bytes from the channel
into length buffers from the array inputs starting with the buffer inputs[offset].
GatheringByteChannel interface:
• int write(ByteBuffer[] outputs) : Writes bytes from the array of buffers outputs to the
channel, and returns the number of bytes written.
• int write(ByteBuffer[] outputs, int offset, int length) : Writes bytes to the channel
from length buffers from the array outputs starting with the buffer outputs[offset].
All of these methods can throw exceptions of one kind or another, and I go into details on these when
you come to apply them. Note that a channel works only with buffers of type ByteBuffer . Other kinds of
buffers do exist as you know, but you can't use them directly with the read() and write() methods for a
channel.