19 mcp servers

Module 19: MCP Servers

Pass MCP server configurations to agents when creating sessions.

What You’ll Learn

• Passing McpServer configs via NewSessionRequest
• Three MCP server types: McpServerStdio, McpServerHttp, McpServerSse
• Checking agent MCP capabilities
• Receiving MCP configs on the agent side

The Code

Client: Pass MCP servers to agent

// Check what MCP transports the agent supports
NegotiatedCapabilities agentCaps = client.getAgentCapabilities();
System.out.println("HTTP: " + agentCaps.supportsMcpHttp());
System.out.println("SSE: " + agentCaps.supportsMcpSse());

// Session with STDIO MCP server
var session1 = client.newSession(new NewSessionRequest(cwd, List.of(
    new McpServerStdio(
        "filesystem",
        "npx",
        List.of("-y", "@modelcontextprotocol/server-filesystem", "/tmp"),
        List.of())
)));

// Session with multiple server types
var session2 = client.newSession(new NewSessionRequest(cwd, List.of(
    new McpServerStdio("git", "npx",
        List.of("-y", "@modelcontextprotocol/server-git"), List.of()),
    new McpServerHttp("weather-api",
        "https://api.weather.example.com/mcp", List.of()),
    new McpServerSse("live-data",
        "https://stream.example.com/mcp/events", List.of())
)));

Agent: Receive and advertise MCP support

.initializeHandler(req -> {
    var mcpCaps = new McpCapabilities(true, true); // HTTP and SSE
    var agentCaps = new AgentCapabilities(
        true, mcpCaps, new PromptCapabilities());
    return InitializeResponse.ok(agentCaps);
})

.newSessionHandler(req -> {
    // MCP servers arrive with the session
    List<McpServer> servers = req.mcpServers();
    for (McpServer server : servers) {
        switch (server) {
            case McpServerStdio s ->
                System.out.println("STDIO: " + s.name() + " " + s.command());
            case McpServerHttp h ->
                System.out.println("HTTP: " + h.name() + " " + h.url());
            case McpServerSse s ->
                System.out.println("SSE: " + s.name() + " " + s.url());
            default -> {}
        }
    }
    return new NewSessionResponse(sessionId, null, null);
})

MCP Server Types

Type	Transport	Use Case
McpServerStdio	Stdin/stdout subprocess	Local tools (filesystem, git)
McpServerHttp	HTTP endpoint	Remote APIs
McpServerSse	Server-sent events	Streaming data

The client tells the agent which MCP servers are available. The agent is responsible for connecting to them using an MCP client library. ACP handles the configuration exchange — not the MCP connection itself.

Source Code

View on GitHub

Running the Example

./mvnw package -pl module-19-mcp-servers -q
./mvnw exec:java -pl module-19-mcp-servers

Next Module

Module 21: Async Client — use the reactive, non-blocking client API.