WireMock Java Stubs vs an OpenAPI Mock Server
Short answer: Java stubs are expressive and live in the test code; a spec mock is generated from the contract and serves every language. The first is a code-level description of the API; the second is a rendering of the source. The boundary is the JVM.
What Java stubs guarantee
Maximum control over matching, transformations, and state in the same language as the tests. They are a separate, maintained description of the API.
What a spec mock guarantees
| Property | Java stubs | Spec mock |
|---|---|---|
| Source | Test code | Contract |
| Language | JVM | Any |
| On change | Update code | On save |
| Drift | Common | Rare |
Why the language boundary matters
A JVM mock serves the JVM tests. A spec mock serves every client, so a polyglot team shares one target.
The decision rule
Java stubs are right for a JVM codebase that wants control. A spec mock is right for a multi-language team that wants the contract to own the mock.
This is part of the Powerduck vs WireMock comparison. Next, read spec vs code.