init fails for Streamable http for java

[anandkrrai]

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Your Question

HI Team,
I am trying to initialize the MCP sync client for streamable http transport. I am doing following :

		HttpClientStreamableHttpTransport streamableHttpTransport = HttpClientStreamableHttpTransport
			.builder("https://qbiz-mcp.abhjaw.people.aws.dev")
			.build();
			
		McpSyncClient client = McpClient.sync(streamableHttpTransport)
			.requestTimeout(Duration.ofSeconds(10))
			.capabilities(McpSchema.ClientCapabilities.builder()
				.roots(true)      // Enable roots capability
				.sampling()       // Enable sampling capability
				.build())
			.build();

		// Initialize connection
		client.initialize();

		// List available tools
		McpSchema.ListToolsResult tools = client.listTools();

I have updated the DEFAULT_ENDPOINT in the HttpClientStreamableHttpTransport to /mcp/ to aoid any redirects.

From the following logs, i have made sure that that the notifications/initialized call sends a 202 response.

2025-07-18 01:24:15 [HttpClient-1-Worker-0] INFO  i.m.c.t.HttpClientStreamableHttpTransport - Sending sessionId 4e66d9e48d154e1290c96662e5d71754
2025-07-18 01:24:15 [HttpClient-1-Worker-0] INFO  i.m.c.t.HttpClientStreamableHttpTransport - uri https://qbiz-mcp.abhjaw.people.aws.dev/mcp/
2025-07-18 01:24:15 [HttpClient-1-Worker-0] INFO  i.m.c.t.HttpClientStreamableHttpTransport - Sending request https://qbiz-mcp.abhjaw.people.aws.dev/mcp/ POST
2025-07-18 01:24:15 [HttpClient-1-Worker-0] INFO  i.m.c.t.HttpClientStreamableHttpTransport - Sending request uri https://qbiz-mcp.abhjaw.people.aws.dev/mcp/
2025-07-18 01:24:15 [HttpClient-1-Worker-0] INFO  i.m.c.t.HttpClientStreamableHttpTransport - Sending request headers java.net.http.HttpHeaders@f64cc5b8 { {Accept=[text/event-stream, application/json], Cache-Control=[no-cache], Content-Type=[application/json], mcp-session-id=[4e66d9e48d154e1290c96662e5d71754]} }
2025-07-18 01:24:15 [HttpClient-1-Worker-0] INFO  i.m.c.t.HttpClientStreamableHttpTransport - Sending request body Optional[jdk.internal.net.http.RequestPublishers$StringPublisher@303bfa30]
2025-07-18 01:24:15 [HttpClient-1-Worker-0] INFO  i.m.c.t.HttpClientStreamableHttpTransport - Sending request jsonBody {"jsonrpc":"2.0","method":"notifications/initialized","params":{"protocolVersion":"2025-06-18","capabilities":{"roots":{"listChanged":true},"sampling":{}},"clientInfo":{"name":"Java SDK MCP Client","version":"1.0.0"}}}
2025-07-18 01:24:15 [HttpClient-1-Worker-0] INFO  i.m.c.t.HttpClientStreamableHttpTransport - response body handler io.modelcontextprotocol.client.transport.HttpClientStreamableHttpTransport$$Lambda/0x000007f8013cade8@59c44cae
2025-07-18 01:24:15 [HttpClient-1-Worker-0] INFO  i.m.c.t.HttpClientStreamableHttpTransport - SendMessage finally: onComplete
2025-07-18 01:24:15 [ForkJoinPool.commonPool-worker-1] INFO  i.m.c.t.HttpClientStreamableHttpTransport - Streamable connection established successfully. respons = (POST https://qbiz-mcp.abhjaw.people.aws.dev/mcp/) 200
2025-07-18 01:24:16 [HttpClient-1-Worker-0] INFO  i.m.c.t.HttpClientStreamableHttpTransport - Received response, using string subscriber
2025-07-18 01:24:16 [HttpClient-1-Worker-0] INFO  i.m.c.t.HttpClientStreamableHttpTransport - SendMessage finally: onComplete
2025-07-18 01:24:16 [ForkJoinPool.commonPool-worker-1] INFO  i.m.c.t.HttpClientStreamableHttpTransport - Streamable connection established successfully. respons = (POST https://qbiz-mcp.abhjaw.people.aws.dev/mcp/) 202

After 20 seconds(the time out), the server init fails with following :

2025-07-18 01:24:34 [parallel-1] WARN  i.m.client.LifecycleInitializer - Failed to initialize
java.util.concurrent.TimeoutException: Did not observe any item or terminal signal within 20000ms in 'map' (and no fallback has been configured)
	at reactor.core.publisher.FluxTimeout$TimeoutMainSubscriber.handleTimeout(FluxTimeout.java:296)
	at reactor.core.publisher.FluxTimeout$TimeoutMainSubscriber.doTimeout(FluxTimeout.java:281)
	at reactor.core.publisher.FluxTimeout$TimeoutTimeoutSubscriber.onNext(FluxTimeout.java:420)
	at reactor.core.publisher.FluxOnErrorReturn$ReturnSubscriber.onNext(FluxOnErrorReturn.java:162)
	at reactor.core.publisher.MonoDelay$MonoDelayRunnable.propagateDelay(MonoDelay.java:270)
	at reactor.core.publisher.MonoDelay$MonoDelayRunnable.run(MonoDelay.java:285)
	at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:68)
	at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:28)

I am not sure hot to fix this for Java SDK. Any support is much appreciated.