A custom SPI loader that supports ordering via @LoadLevel, scope (singleton/prototype), caching, and fallback. It is the backbone of Seata's plugin architecture, loading compressors, serializers, registries, and configuration providers. The implementation is self-contained, thread-safe, and could be extracted into any Java project that needs a lightweight, annotation-driven service loading mechanism with priority control.

Part of a multi-version protocol codec suite (v0, v1, v2) that demonstrates a clean pattern for handling network protocol evolution. It decodes Seata RPC messages from Netty ByteBuf, supporting header maps, compression, and serialization. The versioning strategy (via ProtocolDetectHandler that routes to the correct decoder) is a reusable architectural pattern for any system that needs backward-compatible wire protocol upgrades.

A token-bucket rate limiter used to protect the TC server from excessive requests. It is implemented as a standalone handler with configurable capacity and refill rate, and is integrated via a decorator/filter pattern. The implementation is algorithmically clean (uses a well-known sliding-window token bucket) and can be extracted into any server-side application needing simple, thread-safe rate limiting without external dependencies.