Necord is a NestJS module for creating Discord bots that integrates Discord.js with the NestJS dependency injection system. It provides decorators for defining Discord interactions (slash commands, context menus, message components, modals, etc.) and handles event listening through a discovery mechanism. The architecture follows NestJS patterns with modules, providers, and decorators, using explorer services to scan for decorated methods at runtime. Key features include automatic command registration, custom parameter decorators for interaction data, and advanced context management for asynchronous event handlers using Node.js async_hooks.
Discord4J is a reactive, modular Java library for building Discord bots. It provides a high-level abstraction over Discord's REST API, Gateway WebSocket, and Voice protocols, built on Project Reactor and Netty. The library is structured into separate modules: `common` (shared utilities, store abstraction, rate limiting), `rest` (HTTP client with rate limiting and retry), `gateway` (WebSocket client with state management), `core` (domain objects, event system, spec builders), `voice` (voice connection with encryption and DAVE protocol), and `oauth2` (OAuth2 authentication). The architecture follows a layered design with pluggable components for caching (StoreLayout), rate limiting (GlobalRateLimiter), serialization (ExchangeStrategies), and event dispatching. The codebase demonstrates strong software engineering practices: extensive use of immutable specs via the Immutables library, reactive streams for all I/O, and a comprehensive event hierarchy mirroring Discord's API. However, it contains a mix of deprecated legacy specs and newer immutable specs, some experimental features, and a few duplicated utilities. Overall, it is a well-crafted, production-ready library with active maintenance and good reusability in its core patterns.