Java MCP server with Streamable HTTP, Netty transports, and stateless deployment

Tachyon MCP, a Java 21 Model Context Protocol server built on Netty 4.2, has been released with full support for the MCP 2025-11-25 spec including Streamable HTTP transport, session lifecycle, native I/O transports, and a stateless mode for serverless deployments. The server implements JSON-RPC 2.0, pagination, CORS, DNS rebinding protection, and features like tools, resources, prompts, tasks, and logging with extensible handlers.

Tachyon MCP — A Java 21 Model Context Protocol https://modelcontextprotocol.io MCP server built on Netty 4.2 https://netty.io . Fully implements MCP spec 2025-11-25 Streamable HTTP transport, session lifecycle, native I/O transports, and a stateless mode for serverless deployments. TL;DR python import dev.tachyonmcp.server.TachyonMcpServer; import dev.tachyonmcp.server.features.tools.AbstractSyncToolHandler; import dev.tachyonmcp.server.features.tools.ToolDescriptor; import dev.tachyonmcp.server.features.tools.ToolResult; import dev.tachyonmcp.server.session.McpContext; import tools.jackson.databind.node.JsonNodeFactory; void main { var schema = JsonNodeFactory.instance.objectNode ; schema.put "type", "object" ; schema.putObject "properties" .putObject "city" .put "type", "string" ; TachyonMcpServer.builder .name "weather-mcp" .tool new AbstractSyncToolHandler ToolDescriptor.builder "get forecast" .description "Get weather forecast" .inputSchema schema .build { @Override public Object handle McpContext ctx, Object args { return ToolResult.text "☀️ 22°C" ; } } .stateless true .port 8080 .bind ; } - JSON-RPC 2.0 — request/response/error/notification - Streamable HTTP — POST, GET SSE , DELETE, OPTIONS - Lifecycle — initialize → initialized → ACTIVE - Pagination — cursor-based across all list methods - Session state machine — INITIALIZING → ACTIVE → CLOSED - CORS & origin validation - DNS rebinding protection - Accept header strict validation 406 - Pending request timeout 60s - SSE resumability via Last-Event-ID tools/list — paginated with nextCursor tools/call — returns CallToolResult with isError outputSchema in listing annotations field execution.taskSupport forbidden/optional/required - Synchronous & asynchronous handler interfaces - Name validation 1–128 chars notifications/tools/list changed on add/remove- Inline notifications + logging during tool call - Input schema validation resources/list — paginated resources/read — text & blob content resources/templates/list — URI templates resources/subscribe / unsubscribe notifications/resources/list changed notifications/resources/updated to subscribers- Dynamic content via ResourceHandler interface prompts/list — paginated with nextCursor prompts/get — invokes prompt resolver notifications/prompts/list changed tasks/list , tasks/get , tasks/cancel , tasks/result - State machine enforcement — SUBMITTED → WORKING → COMPLETED/FAILED/CANCELLED notifications/tasks/status broadcast on every transition- Task Janitor for stale tasks execution.taskSupport per tool forbidden/optional/required TasksExtension SEP-1686 https://modelcontextprotocol.io/seps/1686-tasks — negotiable extension exposing create task tool + task://{id} resource template- Extension-gated tool visibility hidden from un-negotiated clients logging/setLevel per session notifications/message emitted above threshold- Progress notifications sampling/createMessage — server → client request- Elicitation — ✅ form mode; ❌ url mode notifications/cancelled — bidirectional notifications/tasks/status from client - Netty 4.2 - io uring / epoll / kqueue / nio auto-detection - Platform-thread event loops + virtual-thread handlers - TCP NODELAY, SO KEEPALIVE - Channel writability backpressure setAutoRead - Configurable idle timeouts reader/writer Stateless mode — skip sessions for serverless- IN MEMORY session store ConcurrentHashMap - Session Janitor — 5s sweep, 30s TTL - SSE disconnect ≠ session removal supports reconnect - Event log replay on reconnection Requirements : JDK 21+ <dependency <groupId dev.tachyonmcp</groupId <artifactId tachyon-server</artifactId <version 1.0.0-alpha.2</version </dependency git clone https://github.com/kpavlov/tachyon.git cd tachyon mvn install -pl tachyon-mcp-server -DskipTests python import dev.tachyonmcp.server.TachyonMcpServer; import dev.tachyonmcp.server.features.tools.AbstractSyncToolHandler; import dev.tachyonmcp.server.features.tools.ToolDescriptor; import dev.tachyonmcp.server.features.tools.ToolResult; import dev.tachyonmcp.server.session.McpContext; import tools.jackson.databind.node.JsonNodeFactory; void main { var schema = JsonNodeFactory.instance.objectNode ; schema.put "type", "object" ; schema.putObject "properties" .putObject "city" .put "type", "string" ; TachyonMcpServer.builder .name "weather-mcp" .tool new AbstractSyncToolHandler ToolDescriptor.builder "get forecast" .description "Get weather forecast" .inputSchema schema .build { @Override public Object handle McpContext ctx, Object args { return ToolResult.text "☀️ 22°C" ; } } .stateless true // start in stateless node no sessions .port 8080 // bind to 1270.0.1:8080 .bind ; } With TasksExtension negotiable - SEP-1686 https://modelcontextprotocol.io/seps/1686-tasks js var handle = TachyonMcpServer.builder .extension new TasksExtension // exposes create task tool + task://{id} resource .port 8080 .bind ; Clients that include "extensions": {"io.modelcontextprotocol/tasks": {}} in their initialize capabilities receive the extension's tool and resource template. Clients that don't negotiate the extension see standard MCP tasks via tasks/list / tasks/get . Handler interfaces ToolHandler , ResourceHandler , PromptHandler and descriptor types use stable domain types. When Tachyon upgrades to a new protocol version, only the internal mapper layer changes; handler implementations are unaffected. Domain types track the 2026-07-28 spec shape where it improves on 2025-11-25 e.g. Annotations.lastModified , ResourceLink in ContentBlock . Native transports — io uring epoll kqueue NIO auto-detect Write buffer watermarks — 32 KB low / 128 KB high, backpressure wired Batch flushing — ctx.write accumulates, single ctx.flush on boundary Minimal allocations — McpEndpointHandler is @Sharable , no per-request handler creation Virtual threads — handlers offloaded from event loop, no manual thread pools JSON-RPC — Jackson streaming codec, no ObjectMapper. - Rate limiting — Not yet implemented - URL elicitation mode / -32042 error — Form mode works, URL mode missing - 2026-07-28 draft protocol version — Not negotiable; version-gated features ready - Stale session on re-initialize — 30s TTL lingering, affects reconnect only Yes. Use stateless true to skip session persistence. Each invocation processes one request independently. Not yet. The current pipeline targets HTTP/1.1; HTTP/2 upgrade is a pipeline configuration change comming soon. Extend AbstractSyncToolHandler or AbstractAsyncToolHandler , passing a ToolDescriptor : class MyTool extends AbstractSyncToolHandler { MyTool { super ToolDescriptor.builder "my tool" .description "Does something useful" .inputSchema buildSchema .build ; } @Override public Object handle McpContext ctx, Object args throws Exception { return CallToolResult.ofText "done" ; } private static JsonNode buildSchema { var s = JsonNodeFactory.instance.objectNode ; s.put "type", "object" ; return s; } } server.resources .add ResourceDescriptor.of "custom://data" , ctx, req - new TextResourceContents "content", req.uri , "text/plain", null ; Tachyon MCP is available under the terms of the Apache 2.0 /kpavlov/tachyon/blob/main/LICENSE .