Java Interop Boundary Design

Interop is easiest to maintain when it is treated as an architectural boundary, not a convenience hack.

For Java engineers, a useful checklist:

• Localize interop in a small set of namespaces.
• Convert types once at the edge; keep your core on persistent data.
• Handle null defensively and decide on a clear nil convention.
• Avoid reflection in hot paths (type hints when needed; measure first).
• Keep effects explicit (resource lifecycles, thread pools, blocking calls).

If you get the boundary right, you can use Java libraries aggressively without losing the benefits that brought you to Clojure in the first place.

In this section

• Code Organization for Clojure and Java Interoperability
  Organize Java and Clojure code around explicit boundary namespaces, clear ownership, data conversion points, and build structure that keeps interop from spreading everywhere.
• Exception Boundaries Between Java and Clojure
  Decide where Java exceptions should be caught, wrapped, translated, or allowed to cross the Clojure boundary so failures remain meaningful to both callers and operators.
• Testing Java and Clojure Interop Code
  Test Java/Clojure boundary code with focused unit tests, integration checks, fixture data, and test doubles that verify conversion, exceptions, resources, and classpath behavior.
• Maintaining Java and Clojure Systems
  Maintain mixed Java/Clojure systems with clear ownership, documented seams, dependency discipline, observability around boundaries, and team conventions for reviewing interop code.