feat(examples): add Java WebFlux MCP server example

[apappascs]

• Spring Boot 3.5 + MCP Java SDK 0.17.2 with WebFlux Streamable HTTP transport
• calculate tool with add, subtract, multiply, divide operations
• interactive calculator UI via ext-apps SDK (CDN)
• 3 MCP prompts: quick-calc, compare-numbers, percentage
• CSP metadata on content items for unpkg.com script loading

Summary

Add a Java WebFlux example server demonstrating the MCP Java SDK with Spring Boot and Streamable HTTP transport.

Motivation and Context

The existing examples are all TypeScript/Python. This adds the first Java example, showing how to build an MCP Apps server using the official MCP Java SDK (mcp-spring-webflux) with Spring Boot WebFlux and Streamable HTTP transport. It serves as a starter template for Java developers.

How Has This Been Tested?

• 18 unit tests (16 tool tests, 2 resource tests)
• End-to-end verification against all MCP endpoints (initialize, tools/list, tools/call, resources/list, resources/read, prompts/list, prompts/get)
• Tested with MCP Inspector
• Tested through Claude.ai web page via Cloudflare tunnel

Breaking Changes

None. This is a new example — no existing code is modified.

Types of changes

• New Example (non-breaking change which adds functionality)

Checklist

• I have read the https://modelcontextprotocol.io
• 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

• Uses MCP Java SDK 0.17.2 (io.modelcontextprotocol.sdk:mcp-spring-webflux)
• Spring Boot 3.5.10 with WebFlux (Netty) — HTTP only, no stdio support
• Clean separation: McpConfig, CalculatorTools, CalculatorResources, CalculatorPrompts
• View HTML loads ext-apps SDK from CDN (unpkg.com) with proper CSP metadata on contents[]._meta
• Maven wrapper included — only requires Java 17+, no global Maven install

[apappascs]

cc: @tzolov

[schlpbch]

Here's my Open Source example example using Java 25 with Virtual Threads and Spring Boot 4.0 / Spring AI 2.0.

https://github.com/schlpbch/open-meteo-mcp-java

The Open-Meteo MCP Java server provides weather, air quality, and conversational AI capabilities through three distinct API endpoints with enterprise-grade security and real-time streaming in a modular, containerized architecture:

🔌 Three API Endpoints
🌐 REST API - Traditional HTTP REST endpoints for direct integration
🔗 MCP API - Model Context Protocol for AI tool integration (Claude Desktop, IDEs)
💬 Chat API - Conversational interface with weather expertise and memory
📡 Streaming API - Real-time SSE streaming for weather data and AI chat responses

[schlpbch]

If interested I gladly extract only the MCP part and contribute!