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MCP Integration

Spring Prism now protects Java applications acting as MCP clients.

Tooling Guides​

If you want a practical setup guide for real tools, start here:

What Ships Today​

The current MCP support lives in prism-mcp and focuses on the client boundary first:

  • outbound payload sanitization before JSON-RPC requests leave the trusted application
  • inbound token restoration after MCP responses return
  • recursive walking of strings inside nested maps, lists, prompt fields, tool arguments, and textual result payloads
  • protocol-aware handling for common MCP shapes such as tool arguments, message content blocks, and JSON-encoded structured argument payloads
  • stronger Streamable HTTP event parsing for multi-line data: frames, progress events, request-id correlation, and [DONE] style trailers
  • fail-open behavior by default, with strict mode available through starter properties
  • runtime metrics aligned with the existing Spring AI and LangChain4j integrations
  • dashboard timing cards and history rollups now include MCP transport activity instead of treating MCP traffic as invisible background load

Supported Transports​

Spring Prism currently supports the two standard MCP transport shapes:

  • stdio for local subprocess servers launched via npx, binaries, or scripts
  • Streamable HTTP for hosted, internal, or containerized MCP servers

Docker is treated as a deployment detail on top of those transports, not as a separate Prism integration layer.

Starter Properties​

spring:
  prism:
    mcp:
      enabled: true
      transport: stdio
      stdio:
        command: java
        args:
          - -jar
          - fake-mcp-server.jar

For hosted MCP endpoints:

spring:
  prism:
    mcp:
      enabled: true
      transport: streamable-http
      http:
        base-url: http://localhost:8081/mcp

Available MCP-specific settings:

  • spring.prism.mcp.enabled
  • spring.prism.mcp.transport
  • spring.prism.mcp.http.base-url
  • spring.prism.mcp.stdio.command
  • spring.prism.mcp.stdio.args
  • spring.prism.mcp.stdio.working-directory
  • spring.prism.mcp.stdio.env[...]
Deprecation

Property spring.prism.mcp.security-strict-mode is deprecated and will be removed in v2.0.0. Use the top-level spring.prism.failure-mode instead.

If spring.prism.mcp.security-strict-mode is not set, the starter inherits the global spring.prism.failure-mode value.

Example App​

The runnable sample lives in prism-examples/mcp-example.

Its integration test uses a fake local stdio MCP server to prove:

  • the external MCP server only sees tokenized values
  • the application receives restored PII on the way back in
  • the embedded dashboard and /actuator/prism surface still work with MCP traffic in the mix

Current Boundary​

This milestone intentionally covers the MCP client role first.

Deferred MCP work:

  • full server-side interception wiring, although a reusable server interceptor foundation now exists in prism-mcp
  • binary payload rewriting
  • richer long-lived streaming response session management beyond the current request-correlated transport support