netty

Netty is an open-source asynchronous event-driven network application framework for rapid development of maintainable high-performance protocol servers and clients. It is written in Java and runs on the Java Virtual Machine, using a non-blocking I/O model to support a large number of concurrent connections with relatively few threads.

The framework centers on channels, pipelines, and handlers. A Channel represents a connection, while a ChannelPipeline is a chain of ChannelHandlers that process inbound and outbound events and data. I/O operations are carried out by one or more EventLoopGroups, each containing EventLoop threads. Netty’s ByteBuf provides a high-performance, reference-counted buffer with pooling capabilities, replacing the standard ByteBuffer for more efficient memory management. The API is asynchronous and event-driven, with ChannelFuture and related mechanisms to observe operation completion.

Netty supports a broad range of transports and protocols, most commonly TCP and UDP, as well as higher-level protocols such as HTTP, WebSocket, and TLS/SSL. It includes codecs and utilities to simplify framing, encoding, and decoding, and offers facilities to implement custom application-layer protocols. The framework emphasizes performance and low latency, featuring zero-copy data transfer, buffer pooling, and scalable channel management.

Netty is used by many Java projects and services that require scalable network communication, including servers, proxies, and clients in microservices architectures. It is maintained as an open-source project under the Apache License 2.0, with origins in JBoss and subsequent development under the Apache Software Foundation.