The Service Layer: Where Separate Components Become a System

This is Part 4 of a series building a production-ready semantic search API with Java, Spring Boot, and pgvector. Part 1 covered the architecture. Part 2 defined the schema. Part 3 handled the embeddings — how text becomes vectors. Each piece worked in isolation. But systems don't fail in isolation — they fail at the boundaries. If you've ever built a feature that worked perfectly on its own but broke the moment you connected it to everything else — this article is about preventing that.