refactor: introduce MCP client customization support

Add McpSyncClientCustomizer interface for customizing MCP sync clients
Replace McpClientDefinitions with McpSyncClientConfigurer
Refactor MCP client initialization to support customization
Remove redundant close() method from McpToolCallback
Fix conditional class dependencies in WebMvc/Flux configurations

Author: tzolov

mcp/common/src/main/java/org/springframework/ai/mcp/McpSyncClientCustomizer.java

@@ -0,0 +1,28 @@
+/*
+* 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;
+
+import io.modelcontextprotocol.client.McpClient;
+
+/**
+ * @author Christian Tzolov
+ * @since 1.0.0
+ */
+public interface McpSyncClientCustomizer {
+
+	void customize(String name, McpClient.SyncSpec sync);
+
+}

mcp/common/src/main/java/org/springframework/ai/mcp/McpToolCallback.java

@@ -112,8 +112,4 @@ public String call(String functionInput) {
 		return ModelOptionsUtils.toJsonString(response.content());
 	}
 
-	public void close() {
-		this.mcpClient.close();
-	}
-
 }

spring-ai-spring-boot-autoconfigure/src/main/java/org/springframework/ai/autoconfigure/mcp/client/stdio/McpClientDefinitions.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2025-2025 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.autoconfigure.mcp.client.stdio;
+
+import java.util.List;
+
+import io.modelcontextprotocol.client.McpClient;
+
+import org.springframework.ai.mcp.McpSyncClientCustomizer;
+
+public class McpSyncClientConfigurer {
+
+	private List<McpSyncClientCustomizer> customizers;
+
+	void setCustomizers(List<McpSyncClientCustomizer> customizers) {
+		this.customizers = customizers;
+	}
+
+	public McpClient.SyncSpec configure(String name, McpClient.SyncSpec spec) {
+		applyCustomizers(name, spec);
+		return spec;
+	}
+
+	private void applyCustomizers(String name, McpClient.SyncSpec spec) {
+		if (this.customizers != null) {
+			for (McpSyncClientCustomizer customizer : this.customizers) {
+				customizer.customize(name, spec);
+			}
+		}
+	}
+
+}

spring-ai-spring-boot-autoconfigure/src/main/java/org/springframework/ai/autoconfigure/mcp/client/stdio/McpSyncClientConfigurer.java

@@ -17,33 +17,26 @@
 package org.springframework.ai.autoconfigure.mcp.client.stdio;
 
 import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.function.Consumer;
-import java.util.function.Function;
 
 import io.modelcontextprotocol.client.McpClient;
 import io.modelcontextprotocol.client.McpSyncClient;
 import io.modelcontextprotocol.client.transport.ServerParameters;
 import io.modelcontextprotocol.client.transport.StdioClientTransport;
 import io.modelcontextprotocol.spec.McpSchema;
-import io.modelcontextprotocol.spec.McpSchema.CreateMessageRequest;
-import io.modelcontextprotocol.spec.McpSchema.CreateMessageResult;
-import io.modelcontextprotocol.spec.McpSchema.Root;
 
-import org.springframework.ai.autoconfigure.mcp.client.stdio.McpClientDefinitions.McpClientDefinition;
+import org.springframework.ai.mcp.McpSyncClientCustomizer;
 import org.springframework.ai.mcp.McpToolCallback;
-import org.springframework.ai.mcp.SyncMcpToolCallbackProvider;
+import org.springframework.ai.mcp.McpToolUtils;
+import org.springframework.ai.tool.ToolCallback;
 import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.autoconfigure.AutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.context.annotation.Bean;
-import org.springframework.core.log.LogAccessor;
-import org.springframework.util.CollectionUtils;
 
 /**
  * Auto-configuration for Model Context Protocol (MCP) STDIO clients.
@@ -81,19 +74,62 @@
 @ConditionalOnProperty(prefix = McpStdioClientProperties.CONFIG_PREFIX, name = "enabled", havingValue = "true")
 public class MpcStdioClientAutoConfiguration {
 
-	private static final LogAccessor logger = new LogAccessor(MpcStdioClientAutoConfiguration.class);
-
 	@Bean
-	public McpClientDefinitions mcpClientDefinitions(McpStdioClientProperties clientProperties) {
+	public List<McpSyncClient> mcpSyncClients(McpSyncClientConfigurer mcpSyncClientConfigurer,
+			McpStdioClientProperties clientProperties) {
 
-		Map<String, McpClientDefinition> definitions = new HashMap<>();
+		List<McpSyncClient> clients = new ArrayList<>();
 
 		for (Map.Entry<String, ServerParameters> serverParameters : clientProperties.toServerParameters().entrySet()) {
-			definitions.put(serverParameters.getKey(),
-					new McpClientDefinition(serverParameters.getKey(), serverParameters.getValue(), clientProperties));
+
+			var transport = new StdioClientTransport(serverParameters.getValue());
+
+			McpSchema.Implementation clientInfo = new McpSchema.Implementation(serverParameters.getKey(),
+					clientProperties.getVersion());
+
+			McpClient.SyncSpec syncSpec = McpClient.sync(transport)
+				.clientInfo(clientInfo)
+				.requestTimeout(clientProperties.getRequestTimeout());
+
+			syncSpec = mcpSyncClientConfigurer.configure(serverParameters.getKey(), syncSpec);
+
+			var syncClient = syncSpec.build();
+
+			if (clientProperties.isInitialize()) {
+				syncClient.initialize();
+			}
+
+			clients.add(syncClient);
+
+		}
+
+		return clients;
+	}
+
+	@Bean
+	public List<ToolCallback> toolCallbacks(List<McpSyncClient> mcpClients) {
+		return McpToolUtils.getToolCallbacks(mcpClients);
+	}
+
+	public record ClosebleMcpSyncClients(List<McpSyncClient> clients) implements AutoCloseable {
+
+		@Override
+		public void close() {
+			clients.forEach(McpSyncClient::close);
 		}
+	}
 
-		return new McpClientDefinitions(definitions);
+	@Bean
+	public ClosebleMcpSyncClients makeThemClosable(List<McpSyncClient> clients) {
+		return new ClosebleMcpSyncClients(clients);
+	}
+
+	@Bean
+	@ConditionalOnMissingBean
+	McpSyncClientConfigurer mcpSyncClientConfigurer(ObjectProvider<McpSyncClientCustomizer> customizerProvider) {
+		McpSyncClientConfigurer configurer = new McpSyncClientConfigurer();
+		configurer.setCustomizers(customizerProvider.orderedStream().toList());
+		return configurer;
 	}
 
 }

spring-ai-spring-boot-autoconfigure/src/main/java/org/springframework/ai/autoconfigure/mcp/client/stdio/MpcStdioClientAutoConfiguration.java

@@ -22,7 +22,8 @@
 /**
  * Configuration properties for the Model Context Protocol (MCP) server.
  * <p>
- * These properties control the behavior and configuration of the MCP server, including:
+ * These properties control the behavior and configuration of the MCP server,
+ * including:
  * <ul>
  * <li>Server identification (name and version)</li>
  * <li>Transport type (STDIO, WEBMVC, or WEBFLUX)</li>
@@ -44,7 +45,8 @@ public class McpServerProperties {
 	/**
 	 * Enable/disable the MCP server.
 	 * <p>
-	 * When set to false, the MCP server and all its components will not be initialized.
+	 * When set to false, the MCP server and all its components will not be
+	 * initialized.
 	 */
 	private boolean enabled = false;
 
@@ -63,16 +65,19 @@ public class McpServerProperties {
 	private String version = "1.0.0";
 
 	/**
-	 * Enable/disable notifications for resource changes. Only relevant for MCP servers
+	 * Enable/disable notifications for resource changes. Only relevant for MCP
+	 * servers
 	 * with resource capabilities.
 	 * <p>
-	 * When enabled, the server will notify clients when resources are added, updated, or
+	 * When enabled, the server will notify clients when resources are added,
+	 * updated, or
 	 * removed.
 	 */
 	private boolean resourceChangeNotification = true;
 
 	/**
-	 * Enable/disable notifications for tool changes. Only relevant for MCP servers with
+	 * Enable/disable notifications for tool changes. Only relevant for MCP servers
+	 * with
 	 * tool capabilities.
 	 * <p>
 	 * When enabled, the server will notify clients when tools are registered or
@@ -81,10 +86,12 @@ public class McpServerProperties {
 	private boolean toolChangeNotification = true;
 
 	/**
-	 * Enable/disable notifications for prompt changes. Only relevant for MCP servers with
+	 * Enable/disable notifications for prompt changes. Only relevant for MCP
+	 * servers with
 	 * prompt capabilities.
 	 * <p>
-	 * When enabled, the server will notify clients when prompt templates are modified.
+	 * When enabled, the server will notify clients when prompt templates are
+	 * modified.
 	 */
 	private boolean promptChangeNotification = true;
 
@@ -152,6 +159,7 @@ public enum ServerType {
 		 * Synchronous (McpSyncServer) server
 		 */
 		SYNC,
+
 		/**
 		 * Asynchronous (McpAsyncServer) server
 		 */

spring-ai-spring-boot-autoconfigure/src/main/java/org/springframework/ai/autoconfigure/mcp/server/McpServerProperties.java

@@ -137,37 +137,37 @@ public McpSyncServer mcpSyncServer(ServerMcpTransport transport,
 				serverProperties.getVersion());
 
 		// Create the server with both tool and resource capabilities
-		SyncSpec serverBilder = McpServer.sync(transport).serverInfo(serverInfo);
+		SyncSpec serverBuilder = McpServer.sync(transport).serverInfo(serverInfo);
 
 		tools.ifAvailable(toolsList -> {
-			serverBilder.tools(toolsList);
+			serverBuilder.tools(toolsList);
 			capabilitiesBuilder.tools(serverProperties.isToolChangeNotification());
 			logger.info("Registered tools" + toolsList.size() + " notification: "
 					+ serverProperties.isToolChangeNotification());
 		});
 
 		resources.ifAvailable(resourceList -> {
-			serverBilder.resources(resourceList);
+			serverBuilder.resources(resourceList);
 			capabilitiesBuilder.resources(false, serverProperties.isResourceChangeNotification());
 			logger.info("Registered resources" + resourceList.size() + " notification: "
 					+ serverProperties.isResourceChangeNotification());
 		});
 
 		prompts.ifAvailable(promptList -> {
-			serverBilder.prompts(promptList);
+			serverBuilder.prompts(promptList);
 			capabilitiesBuilder.prompts(serverProperties.isPromptChangeNotification());
 			logger.info("Registered prompts" + promptList.size() + " notification: "
 					+ serverProperties.isPromptChangeNotification());
 		});
 
 		rootsChangeConsumers.ifAvailable(consumer -> {
-			serverBilder.rootsChangeConsumer(consumer);
+			serverBuilder.rootsChangeConsumer(consumer);
 			logger.info("Registered roots change consumer");
 		});
 
-		serverBilder.capabilities(capabilitiesBuilder.build());
+		serverBuilder.capabilities(capabilitiesBuilder.build());
 
-		return serverBilder.build();
+		return serverBuilder.build();
 	}
 
 	@Bean

spring-ai-spring-boot-autoconfigure/src/main/java/org/springframework/ai/autoconfigure/mcp/server/MpcServerAutoConfiguration.java

@@ -63,7 +63,7 @@
  * @see WebFluxSseServerTransport
  */
 @AutoConfiguration
-@ConditionalOnClass({ WebFluxSseServerTransport.class, RouterFunction.class })
+@ConditionalOnClass({ WebFluxSseServerTransport.class })
 @ConditionalOnProperty(prefix = McpServerProperties.CONFIG_PREFIX, name = "transport", havingValue = "WEBFLUX")
 public class MpcWebFluxServerAutoConfiguration {