NOTE
NIO Channel
Java NIO channel abstractions, partial reads/writes, scattering/gathering, and channel lifecycle.
This is a historical learning note and may contain outdated or incomplete understanding.
A NIO Channel represents an I/O endpoint that works with buffers. File, socket, datagram, and other channel types provide different capabilities.
A single read or write is not guaranteed to consume an entire logical message or buffer. Network code must handle partial progress correctly.
Some channels support scattering/gathering operations across multiple buffers. Close channels explicitly, define ownership of buffers/resources, and keep application message framing separate from the byte-stream/channel abstraction.