Channel
- Java course
- Expert
- Lesson 14/46
- 5 min
Learn the NIO channel with Channel.
The Channel concept
A Channel carries data through a buffer. Unlike streams, a channel can be bidirectional and switch to non-blocking mode. This is more efficient for high-volume IO.
Example: a WritableByteChannel takes a ByteBuffer and writes it to a target with write. With Channels.newChannel(out) an ordinary OutputStream is wrapped as a channel. So stream-based code can work with the NIO channel API. Channels are closed with close.
Channel versus stream
Streams work with single bytes or byte arrays; a channel moves data in blocks through a ByteBuffer. Streams are usually blocking; some channel types can switch to non-blocking mode.
Example: FileChannel opens a channel to a file directly; read and write take a buffer. This is faster than a stream for large files. Methods like transferTo copy data directly from channel to channel. So channels are preferred in high-performance IO.
Practice Write bytes to a channel
Create a ByteArrayOutputStream out. Wrap the channel with WritableByteChannel ch = Channels.newChannel(out). Prepare a two-byte buffer with ByteBuffer.wrap(new byte[]{65, 66}). Write with ch.write(b), close with ch.close(). Print the result of new String(out.toByteArray()) with System.out.println.
Starter code
// Create a ByteArrayOutputStream
// Wrap the channel with Channels.newChannel
// Write and print the resultSample solution
import java.io.ByteArrayOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.WritableByteChannel;
public class ChannelDemo {
public static void main(String[] args) throws Exception {
ByteArrayOutputStream out = new ByteArrayOutputStream();
WritableByteChannel ch = Channels.newChannel(out);
ByteBuffer b = ByteBuffer.wrap(new byte[]{65, 66});
ch.write(b);
ch.close();
System.out.println(new String(out.toByteArray()));
}
}Expected output
AB
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match the Channel concepts
| Term | Meaning |
|---|---|
Channel |
Data channel |
ByteBuffer |
Carried data |
write |
Writes a buffer |
Channels.newChannel |
Stream to channel |
2 What kind of data does a Channel work with?
- Strings
- Characters
- ByteBuffer Correct answer
- Objects
Explanation: A Channel carries data through a ByteBuffer.
3 Complete the Channels.newChannel call
WritableByteChannel ch = Channels.____(out);WritableByteChannel ch = Channels.newChannel(out);Explanation: newChannel wraps a stream as a channel.