feat: Add default logging for MCP notification handlers

- Adds default logging for tools, resources and prompts change notifications.
- Introduces Utils class with collection and string helper methods.
- Ensures notification handlers are always registered with at least a default logging consumer.

Author: tzolov

spring-ai-mcp-core/src/main/java/org/springframework/ai/mcp/client/McpAsyncClient.java

@@ -40,6 +40,7 @@
 import org.springframework.ai.mcp.spec.McpSchema.PaginatedRequest;
 import org.springframework.ai.mcp.spec.McpSchema.Root;
 import org.springframework.ai.mcp.spec.McpTransport;
+import org.springframework.ai.mcp.util.Utils;
 
 /**
  * The Model Context Protocol (MCP) client implementation that provides asynchronous
@@ -85,29 +86,44 @@ public McpAsyncClient(McpTransport transport, Duration requestTimeout,
 			List<Consumer<List<McpSchema.Resource>>> resourcesChangeConsumers,
 			List<Consumer<List<McpSchema.Prompt>>> promptsChangeConsumers) {
 
+		// Request Handlers
 		Map<String, RequestHandler> requestHanlers = new HashMap<>();
 
+		// Roots List Request Handler
 		if (rootsListProviders != null && !rootsListProviders.isEmpty()) {
 			requestHanlers.put("roots/list", rootsListRequestHandler(rootsListProviders));
 			this.rootCapabilities = new McpSchema.ClientCapabilities.RootCapabilities(rootsListChangedNotification);
 		}
 
+		// Notification Handlers
 		Map<String, NotificationHandler> notificationHandlers = new HashMap<>();
 
-		if (toolsChangeConsumers != null && !toolsChangeConsumers.isEmpty()) {
-			notificationHandlers.put("notifications/tools/list_changed",
-					toolsChangeNotificationHandler(toolsChangeConsumers));
+		// Tools Change Notification
+		List<Consumer<List<McpSchema.Tool>>> toolsChangeConsumersFinal = new ArrayList<>();
+		toolsChangeConsumersFinal.add((notification) -> logger.info("Tools changed: {}", notification));
+		if (!Utils.isEmpty(toolsChangeConsumers)) {
+			toolsChangeConsumersFinal.addAll(toolsChangeConsumers);
 		}
-
-		if (resourcesChangeConsumers != null && !resourcesChangeConsumers.isEmpty()) {
-			notificationHandlers.put("notifications/resources/list_changed",
-					resourcesChangeNotificationHandler(resourcesChangeConsumers));
+		notificationHandlers.put("notifications/tools/list_changed",
+				toolsChangeNotificationHandler(toolsChangeConsumersFinal));
+
+		// Resources Change Notification
+		List<Consumer<List<McpSchema.Resource>>> resourcesChangeConsumersFinal = new ArrayList<>();
+		resourcesChangeConsumersFinal.add((notification) -> logger.info("Resources changed: {}", notification));
+		if (!Utils.isEmpty(resourcesChangeConsumers)) {
+			resourcesChangeConsumersFinal.addAll(resourcesChangeConsumers);
 		}
-
-		if (promptsChangeConsumers != null && !promptsChangeConsumers.isEmpty()) {
-			notificationHandlers.put("notifications/prompts/list_changed",
-					promptsChangeNotificationHandler(promptsChangeConsumers));
+		notificationHandlers.put("notifications/resources/list_changed",
+				resourcesChangeNotificationHandler(resourcesChangeConsumersFinal));
+
+		// Prompts Change Notification
+		List<Consumer<List<McpSchema.Prompt>>> promptsChangeConsumersFinal = new ArrayList<>();
+		promptsChangeConsumersFinal.add((notification) -> logger.info("Prompts changed: {}", notification));
+		if (!Utils.isEmpty(promptsChangeConsumers)) {
+			promptsChangeConsumersFinal.addAll(promptsChangeConsumers);
 		}
+		notificationHandlers.put("notifications/prompts/list_changed",
+				promptsChangeNotificationHandler(promptsChangeConsumersFinal));
 
 		this.mcpSession = new DefaultMcpSession(requestTimeout, transport, requestHanlers, notificationHandlers);
 

spring-ai-mcp-core/src/main/java/org/springframework/ai/mcp/util/Utils.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2024-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.ai.mcp.util;
+
+import java.util.Collection;
+import java.util.Map;
+
+import reactor.util.annotation.Nullable;
+
+import org.springframework.lang.Contract;
+
+/**
+ * @author Christian Tzolov
+ */
+
+public class Utils {
+
+	/**
+	 * Check whether the given {@code String} contains actual <em>text</em>.
+	 * <p>
+	 * More specifically, this method returns {@code true} if the {@code String} is not
+	 * {@code null}, its length is greater than 0, and it contains at least one
+	 * non-whitespace character.
+	 * @param str the {@code String} to check (may be {@code null})
+	 * @return {@code true} if the {@code String} is not {@code null}, its length is
+	 * greater than 0, and it does not contain whitespace only
+	 * @see Character#isWhitespace
+	 */
+	public static boolean hasText(@Nullable String str) {
+		return (str != null && !str.isBlank());
+	}
+
+	/**
+	 * Return {@code true} if the supplied Collection is {@code null} or empty. Otherwise,
+	 * return {@code false}.
+	 * @param collection the Collection to check
+	 * @return whether the given Collection is empty
+	 */
+	@Contract("null -> true")
+	public static boolean isEmpty(@Nullable Collection<?> collection) {
+		return (collection == null || collection.isEmpty());
+	}
+
+	/**
+	 * Return {@code true} if the supplied Map is {@code null} or empty. Otherwise, return
+	 * {@code false}.
+	 * @param map the Map to check
+	 * @return whether the given Map is empty
+	 */
+	@Contract("null -> true")
+	public static boolean isEmpty(@Nullable Map<?, ?> map) {
+		return (map == null || map.isEmpty());
+	}
+
+}