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README: update module structure & key decisions with mcp-json removal

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Signed-off-by: Daniel Garnier-Moiroux <git@garnier.wf>
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Daniel Garnier-Moiroux 2026-02-11 17:13:15 +01:00 • committed by Daniel Garnier-Moiroux
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README.md
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@ -83,11 +83,11 @@ The following sections explain what we chose, why it made sense, and how the cho
### 1. JSON Serialization
* **SDK Choice**: Jackson for JSON serialization and deserialization, behind an SDK abstraction (`mcp-json`)
* **SDK Choice**: Jackson for JSON serialization and deserialization, behind an SDK abstraction (package `io.modelcontextprotocol.json` in `mcp-core`)
* **Why**: Jackson is widely adopted across the Java ecosystem, provides strong performance and a mature annotation model, and is familiar to the SDK team and many potential contributors.
* **How we expose it**: Public APIs use a zero-dependency abstraction (`mcp-json`). Jackson is shipped as the default implementation (`mcp-jackson2`), but alternatives can be plugged in.
* **How we expose it**: Public APIs use a bundled abstraction. Jackson is shipped as the default implementation (`mcp-json-jackson3`), but alternatives can be plugged in.
* **How it fits the SDK**: This offers a pragmatic default while keeping flexibility for projects that prefer different JSON libraries.
@ -168,15 +168,26 @@ MCP supports both clients (applications consuming MCP servers) and servers (appl
The SDK is organized into modules to separate concerns and allow adopters to bring in only what they need:
* `mcp-bom` – Dependency versions
* `mcp-core` – Reference implementation (STDIO, JDK HttpClient, Servlet)
* `mcp-json` – JSON abstraction
* `mcp-jackson2` – Jackson implementation of JSON binding
* `mcp` – Convenience bundle (core + Jackson)
* `mcp-core` – Reference implementation (STDIO, JDK HttpClient, Servlet), JSON binding interface definitions
* `mcp-json-jackson2` – Jackson 2 implementation of JSON binding
* `mcp-json-jackson3` – Jackson 3 implementation of JSON binding
* `mcp` – Convenience bundle (core + Jackson 3)
* `mcp-test` – Shared testing utilities
* `mcp-spring` – Spring integrations (WebClient, WebFlux, WebMVC)
For example, a minimal adopter may depend only on `mcp` (core + Jackson), while a Spring-based application can use `mcp-spring` for deeper framework integration.
Additionally, `mcp-test` contains integration tests for `mcp-core`.
`mcp-core` needs a JSON implementation to run full integration tests.
Implementations such as `mcp-json-jackson3`, depend on `mcp-core`, and therefore cannot be imported in `mcp-core` for tests.
Instead, all integration tests that need a JSON implementation are now in `mcp-test`, and use `jackson3` by default.
A `jackson2` maven profile allows to run integration tests with Jackson 2, like so:
```bash
./mvnw -pl mcp-test -am -Pjackson2 test
```
### Future Directions
The SDK is designed to evolve with the Java ecosystem. Areas we are actively watching include: