refactor: introduce session-based architecture for MCP server (#31)

This commit introduces a major refactoring of the MCP Java SDK to implement a session-based architecture
for server-side implementations. The changes improve the SDK's ability to handle multiple concurrent
client connections and provide an API better aligned with the MCP specification.

Key changes:

- Introduce McpServerTransportProvider interface to manage client connections
- Rename ClientMcpTransport to McpClientTransport and ServerMcpTransport to McpServerTransport
- Add exchange objects (McpAsyncServerExchange, McpSyncServerExchange) for client interaction
- Update handler signatures to include exchange parameter: (args) -> result to (exchange, args) -> result
- Rename Registration classes to Specification classes
- Update method names (e.g., rootsChangeConsumers to rootsChangeHandlers)
- Deprecate old interfaces and classes for removal in 0.9.0
- Add migration guide (migration-0.8.0.md)

Resolves #9, #15

Co-authored-by: Christian Tzolov <[email protected]>
Signed-off-by: Christian Tzolov <[email protected]>

Author: chemicL

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

@@ -9,7 +9,7 @@
 
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.ObjectMapper;
-import io.modelcontextprotocol.spec.ClientMcpTransport;
+import io.modelcontextprotocol.spec.McpClientTransport;
 import io.modelcontextprotocol.spec.McpError;
 import io.modelcontextprotocol.spec.McpSchema;
 import io.modelcontextprotocol.spec.McpSchema.JSONRPCMessage;
@@ -58,7 +58,7 @@
  * "https://spec.modelcontextprotocol.io/specification/basic/transports/#http-with-sse">MCP
  * HTTP with SSE Transport Specification</a>
  */
-public class WebFluxSseClientTransport implements ClientMcpTransport {
+public class WebFluxSseClientTransport implements McpClientTransport {
 
 	private static final Logger logger = LoggerFactory.getLogger(WebFluxSseClientTransport.class);
 

mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/server/transport/WebFluxSseServerTransport.java

@@ -60,7 +60,10 @@
  * @author Alexandros Pappas
  * @see ServerMcpTransport
  * @see ServerSentEvent
+ * @deprecated This class will be removed in 0.9.0. Use
+ * {@link WebFluxSseServerTransportProvider}.
  */
+@Deprecated
 public class WebFluxSseServerTransport implements ServerMcpTransport {
 
 	private static final Logger logger = LoggerFactory.getLogger(WebFluxSseServerTransport.class);
@@ -182,16 +185,16 @@ public Mono<Void> sendMessage(McpSchema.JSONRPCMessage message) {
 			try {// @formatter:off
 				String jsonText = objectMapper.writeValueAsString(message);
 				ServerSentEvent<Object> event = ServerSentEvent.builder()
-					.event(MESSAGE_EVENT_TYPE)
-					.data(jsonText)
-					.build();
+				                                               .event(MESSAGE_EVENT_TYPE)
+				                                               .data(jsonText)
+				                                               .build();
 
 				logger.debug("Attempting to broadcast message to {} active sessions", sessions.size());
 
 				List<String> failedSessions = sessions.values().stream()
-					.filter(session -> session.messageSink.tryEmitNext(event).isFailure())
-					.map(session -> session.id)
-					.toList();
+				                                      .filter(session -> session.messageSink.tryEmitNext(event).isFailure())
+				                                      .map(session -> session.id)
+				                                      .toList();
 
 				if (failedSessions.isEmpty()) {
 					logger.debug("Successfully broadcast message to all sessions");
@@ -407,4 +410,4 @@ void close() {
 
 	}
 
-}
+}