Initializing the Protocol

After creating a client, call initialize() before sending any other protocol request. It starts the transport, negotiates the protocol version and capabilities, and sends the notifications/initialized notification.

The Initialize method:

1. Sends an initialize request to the server
2. Logs the server's initialization result
3. Sends an "initialized" notification

After successful initialization, the client can make other requests to the server.

The server validates the initialize payload before negotiation. params and capabilities must be JSON objects; protocolVersion, clientInfo.name, and clientInfo.version must be non-empty strings. Invalid client input is reported as JSON-RPC INVALID_PARAMS instead of an internal error.

Register client capabilities before calling initialize(). For example, call setRoots(...), setSamplingHandler(...), or setElicitationHandler(...) first; only registered handlers are advertised. A server-side call to Roots or Sampling is rejected locally when the target session did not advertise that capability.

Call initialize() immediately after building the McpClient. Initialization uses the configured requestTimeout; zero means wait indefinitely.

McpClient mcpClient = McpClient.builder()
        .clientName("my-host")
        .clientVersion("1.2")
        .transport(sseTransport)
        .build();
        
mcpClient.initialize();