SocketChannel

SocketChannel is a component of Java's NIO (New I/O) framework that represents a selectable channel for stream-oriented connecting sockets, typically TCP. It can operate in blocking or non-blocking mode and is designed to be used with a Selector to handle many connections efficiently. The channel provides read and write operations that transfer data to and from ByteBuffer instances, and it supports registration with a Selector for events such as connect, read, and write.

A SocketChannel is opened by calling its static open method and then connected to a remote address via the connect method. In blocking mode, connect completes before the call returns. In non-blocking mode, connect may return immediately and finishConnect must be invoked when the channel becomes connectable. The channel also exposes the underlying socket through the socket method, allowing access to traditional socket options.

Data transfer uses ByteBuffer objects. Reads may return fewer bytes than requested, and writes may not transfer all bytes in a single operation, so applications typically loop to complete partial I/O. The channel adheres to the channel interfaces in NIO, enabling integration with selectors and non-blocking I/O patterns.

A ServerSocketChannel complements SocketChannel: it listens for incoming connections and, upon acceptance, creates a new SocketChannel for each connected client, enabling scalable server applications.

Closing the channel terminates the connection and releases system resources. SocketChannel is part of the java.nio.channels package and serves as a fundamental primitive for scalable network I/O in Java applications.