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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Stateless server handler throws exception instead of returning JSON-RPC -32601 (Method not found) for not registered capabilities","articleBody":"**Bug description**\nIn the stateless server path (`DefaultMcpStatelessServerHandler`), when a request is received for a method that does not have a registered handler, the server currently throws an `McpError` exception  instead of returning a JSON-RPC response with an error code. This is inconsistent with the stateful/session server implementations (`McpServerSession`, etc.), which respond with the standard JSON-RPC error -32601 (Method not found).\n\n**Environment**\nModelContextProtocol Java SDK, stateless/server mode.\n\n**Steps to reproduce**\n1. Start a stateless MCP server instance (e.g., without advertising or registering a resources or prompts capability).\n2. Send a request with method: \"resources/list\" (or another method for which the handler is not registered).\n3. Exception is thrown instead of returning a JSON-RPC response with a \"Method not found\" error\n\n**Expected behavior**\nStateless server should respond to any unknown/unregistered method with the standard JSON-RPC -32601 \"Method not found\" error, to be consistent with other server implementations in the SDK and with JSON-RPC specification.\n\n**Minimal Complete Reproducible example**\n\nMinimal Spring AI reproducer:\n\n```java\npackage com.example.demo;\n\nimport org.springaicommunity.mcp.annotation.McpTool;\nimport org.springaicommunity.mcp.annotation.McpToolParam;\nimport org.springframework.boot.SpringApplication;\nimport org.springframework.boot.autoconfigure.SpringBootApplication;\nimport org.springframework.stereotype.Component;\n\n@SpringBootApplication\npublic class DemoApplication {\n\n    public static void main(String[] args) {\n        SpringApplication.run(DemoApplication.class, args);\n    }\n\n    @Component\n    public static class DemoTools {\n\n        @McpTool\n        public String hello(@McpToolParam String name) {\n            return \"Hello, \" + name;\n        }\n\n    }\n}\n\n```\n\n```yaml\nspring:\n  ai:\n    mcp:\n      server:\n        enabled: true\n        type: sync\n        protocol: stateless\n        annotation-scanner:\n          enabled: true\n        streamable-http:\n          mcp-endpoint: /mcp\n        capabilities:\n          completion: false\n          prompt: false\n          resource: false\n          tool: true\n```\n\n```xml\n\u003c?xml version=\"1.0\" encoding=\"UTF-8\"?\u003e\n\u003cproject xmlns=\"http://maven.apache.org/POM/4.0.0\" xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\"\n         xsi:schemaLocation=\"http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd\"\u003e\n    \u003cmodelVersion\u003e4.0.0\u003c/modelVersion\u003e\n    \u003cparent\u003e\n        \u003cgroupId\u003eorg.springframework.boot\u003c/groupId\u003e\n        \u003cartifactId\u003espring-boot-starter-parent\u003c/artifactId\u003e\n        \u003cversion\u003e4.0.2\u003c/version\u003e\n        \u003crelativePath/\u003e \u003c!-- lookup parent from repository --\u003e\n    \u003c/parent\u003e\n\n    \u003cgroupId\u003ecom.example\u003c/groupId\u003e\n    \u003cartifactId\u003edemo\u003c/artifactId\u003e\n    \u003cversion\u003e0.0.1-SNAPSHOT\u003c/version\u003e\n    \u003cname\u003edemo\u003c/name\u003e\n    \u003cdescription\u003eDemo project for Spring Boot\u003c/description\u003e\n\n    \u003cproperties\u003e\n        \u003cjava.version\u003e21\u003c/java.version\u003e\n        \u003cspring-ai.version\u003e2.0.0-M2\u003c/spring-ai.version\u003e\n    \u003c/properties\u003e\n\n    \u003cdependencyManagement\u003e\n        \u003cdependencies\u003e\n            \u003cdependency\u003e\n                \u003cgroupId\u003eorg.springframework.ai\u003c/groupId\u003e\n                \u003cartifactId\u003espring-ai-bom\u003c/artifactId\u003e\n                \u003cversion\u003e${spring-ai.version}\u003c/version\u003e\n                \u003ctype\u003epom\u003c/type\u003e\n                \u003cscope\u003eimport\u003c/scope\u003e\n            \u003c/dependency\u003e\n            \u003cdependency\u003e\n                \u003cgroupId\u003eio.modelcontextprotocol.sdk\u003c/groupId\u003e\n                \u003cartifactId\u003emcp-bom\u003c/artifactId\u003e\n                \u003cversion\u003e0.17.2\u003c/version\u003e\n                \u003ctype\u003epom\u003c/type\u003e\n                \u003cscope\u003eimport\u003c/scope\u003e\n            \u003c/dependency\u003e\n        \u003c/dependencies\u003e\n    \u003c/dependencyManagement\u003e\n\n    \u003cdependencies\u003e\n        \u003cdependency\u003e\n            \u003cgroupId\u003eorg.springframework.ai\u003c/groupId\u003e\n            \u003cartifactId\u003espring-ai-starter-mcp-server\u003c/artifactId\u003e\n        \u003c/dependency\u003e\n        \u003cdependency\u003e\n            \u003cgroupId\u003eorg.springframework.ai\u003c/groupId\u003e\n            \u003cartifactId\u003espring-ai-starter-mcp-server-webmvc\u003c/artifactId\u003e\n        \u003c/dependency\u003e\n\n        \u003cdependency\u003e\n            \u003cgroupId\u003eorg.springframework.boot\u003c/groupId\u003e\n            \u003cartifactId\u003espring-boot-starter-test\u003c/artifactId\u003e\n            \u003cscope\u003etest\u003c/scope\u003e\n        \u003c/dependency\u003e\n    \u003c/dependencies\u003e\n\n    \u003cbuild\u003e\n        \u003cplugins\u003e\n            \u003cplugin\u003e\n                \u003cgroupId\u003eorg.springframework.boot\u003c/groupId\u003e\n                \u003cartifactId\u003espring-boot-maven-plugin\u003c/artifactId\u003e\n            \u003c/plugin\u003e\n        \u003c/plugins\u003e\n    \u003c/build\u003e\n\u003c/project\u003e\n```\n\nRunning a `resources/list` command against this server returns a JSON stack trace instead of a JSON-RPC response:\n\n```\n$ curl -H \"Accept: application/json, text/event-stream\" -H \"Content-Type: application/json\" -X POST http://localhost:8080/mcp -d '{\"jsonrpc\": \"2.0\", \"method\": \"resources/list\", \"id\": 1}' | jq\n{\n  \"cause\": null,\n  \"jsonRpcError\": null,\n  \"localizedMessage\": \"Failed to handle request: Missing handler for request type: resources/list\",\n  \"message\": \"Failed to handle request: Missing handler for request type: resources/list\",\n  \"stackTrace\": [\n    {\n      \"classLoaderName\": \"app\",\n      \"className\": \"io.modelcontextprotocol.server.transport.WebMvcStatelessServerTransport\",\n      \"fileName\": \"WebMvcStatelessServerTransport.java\",\n      \"lineNumber\": 126,\n      \"methodName\": \"handlePost\",\n      \"moduleName\": null,\n      \"moduleVersion\": null,\n      \"nativeMethod\": false\n    },\n    {\n      \"classLoaderName\": \"app\",\n      \"className\": \"org.springframework.web.servlet.function.support.HandlerFunctionAdapter\",\n      \"fileName\": \"HandlerFunctionAdapter.java\",\n      // ...\n    },\n    // ...\n  ],\n  \"suppressed\": []\n}\n```","author":{"url":"https://github.com/maff","@type":"Person","name":"maff"},"datePublished":"2026-02-12T20:04:10.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/784/java-sdk/issues/784"}