Moves mcp-json API back into mcp-core for simplified dependencies and support of osgi runtimes by scottslewis · Pull Request #762 · modelcontextprotocol/java-sdk

scottslewis · 2026-01-28T23:54:04Z

mcp-core so that mcp-json API is no longer needed and mcp-core has fewer dependencies.

See issue #612 and previous pr #682

Motivation and Context

Simplifies dependency structure, and reenables ability to use OSGi runtimes #562

How Has This Been Tested?

Have tested in OSGi environments running OSGi application.

Breaking Changes

This eliminates the need to deploy mcp-json jar, meaning that users will only have to (minimally) deploy mcp-core and either mcp-json-jackson2 or mcp-json-jackson3

Types of changes

[X ] Bug fix (non-breaking change which fixes an issue)

Checklist

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

Additional context

To deal with the testing dependencies issues as described here: #682 (comment)

it may be necessary to add further changes/refactoring/moving of the test code (in mcp-core specifically). I'm willing to do or contribute to this refactoring if needed, once consensus is achieved.

…n API back into mcp-core so that mcp-json API is no longer needed and mcp-core has fewer dependencies.

mcp-core/pom.xml

mcp-core/src/main/java/io/modelcontextprotocol/util/McpServiceLoader.java

mcp-core/src/main/java/io/modelcontextprotocol/json/McpJsonDefaults.java

mcp-core/src/main/java/io/modelcontextprotocol/json/internal/DefaultMcpJsonMapperSupplier.java

@LucaButBoring

@LucaButBoring for catch

…Loader.java Co-authored-by: Luca Chang <131398524+LucaButBoring@users.noreply.github.com>

and DefaultMcpJsonSchemaSupplier as they were originally committed accidently. Thanks to LucaButBoring for pointing out the error.

…cp-java-sdk into issue_612_jackson3

filiphr · 2026-01-30T09:34:16Z

@scottslewis, I'm not familiar with OSGi that much, but I have some general questions about the PR.

Why not delete mcp-json in this PR as well?
What is the difference between the mechanism that was being used before in the McpJsonInternal vs the one in this PR with the McpJsonDefaults? Of course taking into consideration the fact the move into mcp-core

scottslewis · 2026-01-30T15:17:54Z

@scottslewis, I'm not familiar with OSGi that much, but I have some general questions about the PR.

Why not delete mcp-json in this PR as well?

I could have...but chose to leave it so that the pr was not as large. If doing it in one step is preferable then that can be done.

What is the difference between the mechanism that was being used before in the McpJsonInternal vs the one in this PR with the McpJsonDefaults? Of course taking into consideration the fact the move into mcp-core

The impl of McpJsonDefaults is key to working (for json defaults) in non osgi and osgi environments. In non osgi environments, the serviceloader is used to find and load jackson2 or jackson3 impl for defaults as done previously.

In osgi, the serviceloader does not work the same...because of classloader-per-bundle as per osgi issue #562. In osgi, mcpjsondefaults is created and configured on start by the osgi sevice registry using scr metadata in manifests.

For clarity here is the McpJsonDefaults scr metadata

filiphr · 2026-01-30T20:34:55Z

Thanks for the explanation @scottslewis, always good to learn a bit more about it.

I could have...but chose to leave it so that the pr was not as large. If doing it in one step is preferable then that can be done.

I think the PR would actually be smaller then, since the classes that are removed, they'll show up as modified moved in git with no changes.

scottslewis · 2026-01-30T20:57:45Z

Thanks for the explanation @scottslewis, always good to learn a bit more about it.

I could have...but chose to leave it so that the pr was not as large. If doing it in one step is preferable then that can be done.

I think the PR would actually be smaller then, since the classes that are removed, they'll show up as modified moved in git with no changes.

Ok, honestly I don't care that much. Let's get the code and build/test/dependency changes reviewed/complete/consensus, etc...without breaking the build and test/CI if possible...and I'll delete or someone else can...whatever the choice is fine by me.

Kehrlann

I agree with @filiphr , remove mcp-json
Please run ./mvnw spring-javaformat:apply
We need test passing before we can merge this

Kehrlann · 2026-02-05T09:36:08Z

mcp-core/src/main/java/io/modelcontextprotocol/json/McpJsonDefaults.java

+		mcpMapperServiceLoader.unsetSupplier(supplier);
+	}
+
+	public synchronized static McpJsonMapper getDefaultMcpJsonMapper() {


[issue] There are two separate synchronized methods, each using constructor side-effects. My understanding is that the synchronized is to avoid calling the constructor twice. If that's the case, in the current state, calling both methods at the same time triggers a race condition.

Kehrlann · 2026-02-05T09:48:04Z

mcp-core/src/main/java/io/modelcontextprotocol/json/McpJsonDefaults.java

@@ -0,0 +1,50 @@
+package io.modelcontextprotocol.json;


Missing license header

Kehrlann · 2026-02-05T09:50:09Z

mcp-core/src/main/java/io/modelcontextprotocol/json/McpJsonDefaults.java

+import io.modelcontextprotocol.json.schema.JsonSchemaValidatorSupplier;
+import io.modelcontextprotocol.util.McpServiceLoader;
+
+public class McpJsonDefaults {


The patterns used here are uncommon in non-OSGi codebases. Please add a note in the javadoc mentioning OSGi compatibility.

Kehrlann · 2026-02-05T09:51:57Z

mcp-core/src/main/java/io/modelcontextprotocol/util/McpServiceLoader.java

@@ -0,0 +1,50 @@
+package io.modelcontextprotocol.util;


Missing license header.

Kehrlann · 2026-02-05T09:52:25Z

mcp-core/src/main/java/io/modelcontextprotocol/util/McpServiceLoader.java

+import java.util.ServiceLoader;
+import java.util.function.Supplier;
+
+public class McpServiceLoader<S extends Supplier<R>, R> {


Same as McpJsonDefaults, mention OSGi here.

Kehrlann · 2026-02-05T09:57:09Z

mcp-core/src/main/java/io/modelcontextprotocol/util/McpServiceLoader.java

+				// Use serviceloader
+				Optional<?> sl = serviceLoad(this.supplierType);
+				if (sl.isEmpty()) {
+					throw new ServiceConfigurationError("No %s available for creating McpJsonMapper".format(this.supplierType.getSimpleName()));


Did you mean to use "...".formatted(...), or String.format("...", ...) ?

Rebasing on main after modelcontextprotocol#742 merged. Moves mcp-jso…

003eb6e

…n API back into mcp-core so that mcp-json API is no longer needed and mcp-core has fewer dependencies.

scottslewis changed the title ~~Rebasing on main after #742 merged. Moves mcp-json API back into mcp-core for simplified dependency and support of osgi runtimes~~ Moves mcp-json API back into mcp-core for simplified dependency and support of osgi runtimes Jan 29, 2026

scottslewis mentioned this pull request Jan 29, 2026

mcp no longer works in OSGi #562

Open

LucaButBoring reviewed Jan 29, 2026

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scottslewis and others added 4 commits January 29, 2026 13:43

Fix for missing <scope>test</scope> in mcp-core. Thanks to

bedf075

@LucaButBoring for catch

Update mcp-core/src/main/java/io/modelcontextprotocol/util/McpService…

fbda61f

…Loader.java Co-authored-by: Luca Chang <131398524+LucaButBoring@users.noreply.github.com>

Removed DefaultMcpJsonMapperSupplier

76ce84d

and DefaultMcpJsonSchemaSupplier as they were originally committed accidently. Thanks to LucaButBoring for pointing out the error.

Merge branch 'issue_612_jackson3' of https://github.com/scottslewis/m…

e6041be

…cp-java-sdk into issue_612_jackson3

scottslewis mentioned this pull request Jan 30, 2026

Refactor of json + json schema validation api into mcp-core #682

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scottslewis changed the title ~~Moves mcp-json API back into mcp-core for simplified dependency and support of osgi runtimes~~ Moves mcp-json API back into mcp-core for simplified dependencies and support of osgi runtimes Jan 30, 2026

scottslewis mentioned this pull request Jan 30, 2026

Decouple mcp-test and mcp-spring modules from Jackson implementation #760

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Kehrlann reviewed Feb 5, 2026

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scottslewis commented Jan 28, 2026

Motivation and Context

How Has This Been Tested?

Breaking Changes

Types of changes

Checklist

Additional context

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filiphr commented Jan 30, 2026

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scottslewis commented Jan 30, 2026 •

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