Mcp-core has compile-time dependency on mcp-json

[scottslewis]

mcp-core project has a compile-time dependency on mcp-json due to the location of these three classes:

/mcp-json/src/main/java/io/modelcontextprotocol/json/McpJsonMapper.java

/mcp-json/src/main/java/io/modelcontextprotocol/json/TypeRef.java

/mcp-json/src/main/java/io/modelcontextprotocol/json/schema/JsonSchemaValidator.java

I would argue that since these classes are required at all times, it doesn't make sense for them to be in a separate jar...as mcp-core jar is useless without mcp-json jar also present.

I would suggest moving these three classes (at least) back to mcp-core (e.g. in package io.modelcontextprotocol.sdk.util or io.modelcontextprotocol.sdk.json. This would allow a clear separation between mapper and schema validator interfaces (in core) and their implementation (default or other).

[tbohr-actico]

May I add another finding that is related to this issue?
Due to the specific bnd-maven-plugin configuration in mcp-core, the class files from mcp-json are assembled into the mcp-core jar. The situation you describe is therefore already evident, albeit in a very unexpected way.

[scottslewis]

I've done an initial refactor in pr #682. This pr moves the json mapper + json schema validation api (without implementation) back into mcp-core, in new packages .json, .json.schema, and .json.internal. With these changes mcp-core no longer has a compile time dependency on mcp-json nor mcp-jackson2. Now that the api that was in mcp-json is in mcp-core packages, mcp-json module is not needed at all (and is removed from the maven build.

mcp-core requires mcp-jackson2 or a new implementation of the a McpJsonMapperSupplier and JsonSchemaValidatorSupplier. IF not configured another way (e.g. via osgi declarative services or 'manually'), the java ServiceLoader is used to load the default McpJsonMapperSupplier and JsonSchemaValidatorSupplier.

I'm planning on adding the OSGi metadata to use an OSGi service impls of McpJsonMapperSupplier and JsonSchemaValidatorSupplier, so that the the osgi service registry can be used instead of the ServiceLoader in osgi environmemts.

[scottslewis]

I'm planning on adding the OSGi metadata to use an OSGi service impls of McpJsonMapperSupplier and JsonSchemaValidatorSupplier, so that the the osgi service registry can be used instead of the ServiceLoader in osgi environmemts.

This has now been added to pr #682 in this commit.

In osgi environments, with these declarative services meta-data (.xml files), the suppliers for both the json mapper and json validator are initialized and dynamically injected into the DefaultMcpJsonMapperSupplier and the DefaultMcpJsonValidatorSupplier by declarative services. These suppliers are then subsequently used (rather than the ServiceLoader.load) to create McpJsonMapper and McpJsonValidator default instances.

[Omkar-Shetkar]

I get maven enforcer duplicate class issue for io/modelcontextprotocol/json/McpJsonMapperSupplier.class.

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-enforcer-plugin:3.6.1:enforce (enforce) on project lang-rt:
[ERROR] Rule 1: org.codehaus.mojo.extraenforcer.dependencies.BanDuplicateClasses failed with message:
[ERROR] Duplicate class found:
[ERROR]
[ERROR]   Found in:
[ERROR]     io.modelcontextprotocol.sdk:mcp-json:jar:0.17.0:compile
[ERROR]     io.modelcontextprotocol.sdk:mcp-core:jar:0.17.0:compile
[ERROR]   Duplicate classes:
[ERROR]     io/modelcontextprotocol/json/McpJsonMapperSupplier.class
[ERROR] There may be others but <findAllDuplicates> was set to false, so failing fast
[ERROR] -> [Help 1]
[ERROR]

I think #682 might resolve this.

[scottslewis]

From previous comment

I think [#682](https://github.com/modelcontextprotocol/java-sdk/pull/682) might resolve this.

I am certain it would. Part of what pr #682 does is eliminate the mcp-json module and jar by moving the mcp-json classes back into mcp-core so that mcp-core can compile without having mcp-json previously compiled.

[chemicL]

Closed via #682