Add Support for Jackson 3 and use it by default

[filiphr]

The goal of this PR is to add support for Jackson 3.

Motivation and Context

Jackson 3 is the latest version from Jackson and it is the next iteration of Jackson.

How Has This Been Tested?

The existing tests were enough

Breaking Changes

The Java MCP SDK now pulls in Jackson 3 instead of Jackson 2. This can be potentially a breaking change in case someone was using io.modelcontextprotocol.json.jackson.JacksonMcpJsonMapper then they would need to switch to io.modelcontextprotocol.json.jackson3.JacksonMcpJsonMapper and / or adjust the dependencies so that they pull mcp-core and mcp-json-jackson3

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[sdeleuze]

@filiphr I was about to submit such PR, so thanks for creating it.

I think I would prefer to have consistency between mcp-json-jackson2 and mcp-json-jackson3 package naming strategy (version-less or with version), see my related #562 (comment) comment, but that would be a breaking change, so let see with the team what is the preferred solution.

[filiphr]

Thanks for your comment @sdeleuze. I've read your comment #562 (comment) and I've added an alternative idea in #562 (comment).

In any case, I stumbled onto this since I wanted to contribute Jackson 3 support for Spring AI, but that depends on this project, so I started here first.

[sdeleuze]

@filiphr Thanks, just be aware I am already working on the Jackson 3 support for Spring AI, and have it pretty advanced locally, so no need to contribute it. That said, I will welcome your review on my upcoming PR.

[sdeleuze]

After the discussion on #562, my proposal is the following:

0.18:

• Introduce mcp-json-jackson3 as implemented in this PR
• In mcp-json-jackson2, deprecate classes for removal in io.modelcontextprotocol.json.jackson/io.modelcontextprotocol.json.schema.jackson and copy them to io.modelcontextprotocol.json.jackson2/io.modelcontextprotocol.json.schema.jackson2 in non-deprecated form.

0.19:

• Remove deprecated classes in io.modelcontextprotocol.json.jackson/io.modelcontextprotocol.json.schema.jackson from mcp-json-jackson2

@filiphr @tzolov @chemicL @graemerocher @sdelamo Are you ok with that? If we are, this PR could be refined with the proposed mcp-json-jackson2 changes for 0.18.

[filiphr]

I'm OK with your proposal @sdeleuze. In an hour or two I can adjust this PR and the the changes in relation to mcp-json-jackson2.

---

@filiphr Thanks, just be aware I am already working on the Jackson 3 support for Spring AI, and have it pretty advanced locally, so no need to contribute it. That said, I will welcome your review on my upcoming PR.

Thanks for letting me know @sdeleuze. I have not spend a lot of time on it anyways, I stumbled fast on the different dependencies. I would be happy to review your PR for Spring AI, feel free to ping me when you have it ready.

[tzolov]

After the discussion on #562, my proposal is the following:

0.18:

• Introduce mcp-json-jackson3 as implemented in this PR
• In mcp-json-jackson2, deprecate classes for removal in io.modelcontextprotocol.json.jackson/io.modelcontextprotocol.json.schema.jackson and copy them to io.modelcontextprotocol.json.jackson2/io.modelcontextprotocol.json.schema.jackson2 in non-deprecated form.

0.19:

• Remove deprecated classes in io.modelcontextprotocol.json.jackson/io.modelcontextprotocol.json.schema.jackson from mcp-json-jackson2

@filiphr @tzolov @chemicL @graemerocher @sdelamo Are you ok with that? If we are, this PR could be refined with the proposed mcp-json-jackson2 changes for 0.18.

@sdeleuze @filiphr

This plan makes sense. Please go ahead

[filiphr]

Thanks for the review. @sdeleuze @tzolov I have implemented the plan like we discussed.

[chemicL]

Thanks. I added a tiny javadoc remark, probably worth rebasing the PR against main and fixing that one.
As a follow up, we should look into unifying the tests between modules as currently they're a copy.

[sdelamo]

it looks good to me.

[filiphr]

Thanks everyone for the review. I had to do some additional changes to make sure everything works with Jackson 3.

• Upgrade Spring Framework to 7.x. Otherwise, the webmvc / webflux support does not work with Jackson 3.
• In io.modelcontextprotocol.json.jackson3.JacksonMcpJsonMapper catch the JacksonException and throw IOException. Otherwise, the webflux tests and most likely some more were failing. In Jackson 3 the base JacksonException no longer extends IOException and it's a runtime exception. I do not like this that much, the alternative would be to go through all the places that are calling the methods of McpJsonMapper and adjust them to capture Exception instead of IOException. Another alternative would be to not throw IOException, but rather have a dedicated McpJsonException and each underlying library can throw that if there is some error in the mapping.

As a follow up, we should look into unifying the tests between modules as currently they're a copy.

I agree with you @chemicL it would be good to have some unified tests, maybe tests where all the different json mappers are tested. Btw, I also had some problems with some of the tests in StdioMcpAsyncClientTests and StdioMcpSyncClientTests with errors like:

java.lang.AssertionError: 
Expecting all elements of:
  [TextContent[annotations=null, text=MCP error -32602: Tool sampleLLM not found, meta=null]]
to satisfy given requirements, but these elements did not:

TextContent[annotations=null, text=MCP error -32602: Tool sampleLLM not found, meta=null]
error: java.lang.AssertionError: 
Expecting actual:
  "MCP error -32602: Tool sampleLLM not found"
to end with:
  "Goodbye, world!"