fix: support customized sse endpoint in WebFluxSseClientTransport

mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/client/transport/WebFluxSseClientTransport.java

@@ -79,7 +79,7 @@ public class WebFluxSseClientTransport implements McpClientTransport {
 	 * Default SSE endpoint path as specified by the MCP transport specification. This
 	 * endpoint is used to establish the SSE connection with the server.
 	 */
-	private static final String SSE_ENDPOINT = "/sse";
+	private static final String DEFAULT_SSE_ENDPOINT = "/sse";
 
 	/**
 	 * Type reference for parsing SSE events containing string data.
@@ -92,6 +92,10 @@ public class WebFluxSseClientTransport implements McpClientTransport {
 	 * for establishing the SSE connection and sending outbound messages.
 	 */
 	private final WebClient webClient;
+	/**
+	 * The SSE endpoint URI provided by the server.
+	 */
+	private final String sseEndpoint;
 
 	/**
 	 * ObjectMapper for serializing outbound messages and deserializing inbound messages.
@@ -137,11 +141,26 @@ public WebFluxSseClientTransport(WebClient.Builder webClientBuilder) {
 	 * @throws IllegalArgumentException if either parameter is null
 	 */
 	public WebFluxSseClientTransport(WebClient.Builder webClientBuilder, ObjectMapper objectMapper) {
+		this(webClientBuilder, objectMapper, DEFAULT_SSE_ENDPOINT);
+	}
+
+	/**
+	 * Constructs a new SseClientTransport with the specified WebClient builder and
+	 * ObjectMapper. Initializes both inbound and outbound message processing pipelines.
+	 * @param webClientBuilder the WebClient.Builder to use for creating the WebClient
+	 * instance
+	 * @param objectMapper the ObjectMapper to use for JSON processing
+	 * @param sseEndpoint the SSE endpoint URI to use for establishing the connection
+	 * @throws IllegalArgumentException if either parameter is null
+	 */
+	public WebFluxSseClientTransport(WebClient.Builder webClientBuilder, ObjectMapper objectMapper, String sseEndpoint) {
 		Assert.notNull(objectMapper, "ObjectMapper must not be null");
 		Assert.notNull(webClientBuilder, "WebClient.Builder must not be null");
+		Assert.notNull(sseEndpoint, "SSE endpoint must not be null");
 
 		this.objectMapper = objectMapper;
 		this.webClient = webClientBuilder.build();
+		this.sseEndpoint = sseEndpoint;
 	}
 
 	/**
@@ -254,7 +273,7 @@ public Mono<Void> sendMessage(JSONRPCMessage message) {
 	protected Flux<ServerSentEvent<String>> eventStream() {// @formatter:off
 		return this.webClient
 			.get()
-			.uri(SSE_ENDPOINT)
+			.uri(sseEndpoint)
 			.accept(MediaType.TEXT_EVENT_STREAM)
 			.retrieve()
 			.bodyToFlux(SSE_TYPE)