[fel] add notification/tools/list_changed method in MCP server (#136)

* [fit] add notification/tools/list_changed method in MCP server

* [fel] add unit test for MCP server

Author: CodeCasterX

framework/fel/java/plugins/tool-mcp-server/pom.xml

@@ -32,9 +32,20 @@
         </dependency>
 
         <!-- Test -->
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>org.assertj</groupId>
             <artifactId>assertj-core</artifactId>
+            <scope>test</scope>
         </dependency>
     </dependencies>
 

framework/fel/java/plugins/tool-mcp-server/src/main/java/modelengine/fel/tool/mcp/server/McpController.java

@@ -48,14 +48,15 @@
  * @since 2025-05-13
  */
 @Component
-public class McpController {
+public class McpController implements McpServer.ToolsChangedObserver {
     private static final Logger log = Logger.get(McpController.class);
     private static final String MESSAGE_PATH = "/mcp/message";
     private static final String EVENT_ENDPOINT = "endpoint";
     private static final String EVENT_MESSAGE = "message";
     private static final String METHOD_INITIALIZE = "initialize";
     private static final String METHOD_TOOLS_LIST = "tools/list";
     private static final String METHOD_TOOLS_CALL = "tools/call";
+    private static final String METHOD_NOTIFICATION_TOOLS_CHANGED = "notifications/tools/list_changed";
     private static final String RESPONSE_OK = StringUtils.EMPTY;
 
     private final Map<String, Emitter<TextEvent>> emitters = new ConcurrentHashMap<>();
@@ -79,6 +80,7 @@ public McpController(@Value("${base-url}") String baseUrl, @Fit(alias = "json")
         this.baseUrl = notBlank(baseUrl, "The base URL for MCP server cannot be blank.");
         this.serializer = notNull(serializer, "The json serializer cannot be null.");
         notNull(mcpServer, "The MCP server cannot be null.");
+        mcpServer.registerToolsChangedObserver(this);
 
         this.methodHandlers.put(METHOD_INITIALIZE, new InitializeHandler(mcpServer));
         this.methodHandlers.put(METHOD_TOOLS_LIST, new ToolListHandler(mcpServer));
@@ -170,4 +172,16 @@ public Object receiveMcpMessage(@RequestQuery(name = "sessionId") String session
         log.info("Send MCP message. [response={}]", serialized);
         return RESPONSE_OK;
     }
+
+    @Override
+    public void onToolsChanged() {
+        JsonRpcEntity notification = new JsonRpcEntity();
+        notification.setMethod(METHOD_NOTIFICATION_TOOLS_CHANGED);
+        String serialized = this.serializer.serialize(notification);
+        this.emitters.forEach((sessionId, emitter) -> {
+            TextEvent textEvent = TextEvent.custom().id(sessionId).event(EVENT_MESSAGE).data(serialized).build();
+            emitter.emit(textEvent);
+            log.info("Send MCP notification: tools changed. [sessionId={}]", sessionId);
+        });
+    }
 }

framework/fel/java/plugins/tool-mcp-server/src/main/java/modelengine/fel/tool/mcp/server/McpServer.java

@@ -40,4 +40,21 @@ public interface McpServer {
      * @return The tool result as a {@link Object}.
      */
     Object callTool(String name, Map<String, Object> arguments);
+
+    /**
+     * Registers MCP Server Tools Changed Observer.
+     *
+     * @param observer The MCP Server Tools Changed Observer as a {@link ToolsChangedObserver}.
+     */
+    void registerToolsChangedObserver(ToolsChangedObserver observer);
+
+    /**
+     * Represents the MCP Server Tools Changed Observer.
+     */
+    interface ToolsChangedObserver {
+        /**
+         * Called when MCP Server Tools changed.
+         */
+        void onToolsChanged();
+    }
 }

framework/fel/java/plugins/tool-mcp-server/src/main/java/modelengine/fel/tool/mcp/server/handler/InitializeHandler.java

@@ -26,7 +26,7 @@ public class InitializeHandler extends AbstractMessageHandler<InitializeHandler.
      * Constructs a new instance of the InitializeHandler class.
      *
      * @param mcpServer The MCP server instance used to retrieve server information during request handling.
-     * @throws IllegalStateException If {@code mcpServer} is null.
+     * @throws IllegalArgumentException If {@code mcpServer} is null.
      */
     public InitializeHandler(McpServer mcpServer) {
         super(InitializeRequest.class);

framework/fel/java/plugins/tool-mcp-server/src/main/java/modelengine/fel/tool/mcp/server/handler/ToolCallHandler.java

@@ -38,7 +38,7 @@ public class ToolCallHandler extends AbstractMessageHandler<ToolCallHandler.Tool
      *
      * @param mcpServer The MCP server instance used to invoke tools during request handling.
      * @param jsonSerializer The serializer used to convert non-string results into JSON strings.
-     * @throws IllegalStateException If {@code mcpServer} or {@code jsonSerializer} is null.
+     * @throws IllegalArgumentException If {@code mcpServer} or {@code jsonSerializer} is null.
      */
     public ToolCallHandler(McpServer mcpServer, ObjectSerializer jsonSerializer) {
         super(ToolCallRequest.class);

framework/fel/java/plugins/tool-mcp-server/src/main/java/modelengine/fel/tool/mcp/server/handler/ToolListHandler.java

@@ -28,7 +28,7 @@ public class ToolListHandler extends AbstractMessageHandler<ToolListHandler.Tool
      * Constructs a new instance of the ToolListHandler class.
      *
      * @param mcpServer The MCP server instance used to retrieve the list of tools during request handling.
-     * @throws IllegalStateException If {@code mcpServer} is null.
+     * @throws IllegalArgumentException If {@code mcpServer} is null.
      */
     public ToolListHandler(McpServer mcpServer) {
         super(ToolListRequest.class);

framework/fel/java/plugins/tool-mcp-server/src/main/java/modelengine/fel/tool/mcp/server/support/DefaultMcpServer.java

@@ -18,6 +18,7 @@
 import modelengine.fitframework.util.MapUtils;
 import modelengine.fitframework.util.StringUtils;
 
+import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
@@ -34,12 +35,13 @@ public class DefaultMcpServer implements McpServer, ToolChangedObserver {
 
     private final ToolExecuteService toolExecuteService;
     private final Map<String, ToolEntity> tools = new ConcurrentHashMap<>();
+    private final List<ToolsChangedObserver> toolsChangedObservers = new ArrayList<>();
 
     /**
      * Constructs a new instance of the DefaultMcpServer class.
      *
      * @param toolExecuteService The service used to execute tools when handling tool call requests.
-     * @throws IllegalStateException If {@code toolExecuteService} is null.
+     * @throws IllegalArgumentException If {@code toolExecuteService} is null.
      */
     public DefaultMcpServer(ToolExecuteService toolExecuteService) {
         this.toolExecuteService = notNull(toolExecuteService, "The tool execute service cannot be null.");
@@ -72,6 +74,13 @@ public Object callTool(String name, Map<String, Object> arguments) {
         return result;
     }
 
+    @Override
+    public void registerToolsChangedObserver(ToolsChangedObserver observer) {
+        if (observer != null) {
+            this.toolsChangedObservers.add(observer);
+        }
+    }
+
     @Override
     public void onToolAdded(String name, String description, Map<String, Object> schema) {
         if (StringUtils.isBlank(name)) {
@@ -92,6 +101,7 @@ public void onToolAdded(String name, String description, Map<String, Object> sch
         tool.setInputSchema(schema);
         this.tools.put(name, tool);
         log.info("Tool added to MCP server. [toolName={}, description={}, schema={}]", name, description, schema);
+        this.toolsChangedObservers.forEach(ToolsChangedObserver::onToolsChanged);
     }
 
     @Override
@@ -102,5 +112,6 @@ public void onToolRemoved(String name) {
         }
         this.tools.remove(name);
         log.info("Tool removed from MCP server. [toolName={}]", name);
+        this.toolsChangedObservers.forEach(ToolsChangedObserver::onToolsChanged);
     }
 }

framework/fel/java/plugins/tool-mcp-server/src/test/java/modelengine/fel/tool/mcp/server/McpControllerTest.java

@@ -0,0 +1,72 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) 2025 Huawei Technologies Co., Ltd. All rights reserved.
+ *  This file is a part of the ModelEngine Project.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+package modelengine.fel.tool.mcp.server;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.catchThrowableOfType;
+import static org.mockito.Mockito.mock;
+
+import modelengine.fitframework.serialization.ObjectSerializer;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit test for {@link McpController}.
+ *
+ * @author 季聿阶
+ * @since 2025-05-20
+ */
+@DisplayName("Unit tests for McpController")
+public class McpControllerTest {
+    private ObjectSerializer objectSerializer;
+    private McpServer mcpServer;
+    private String baseUrl;
+
+    @BeforeEach
+    void setup() {
+        this.objectSerializer = mock(ObjectSerializer.class);
+        this.mcpServer = mock(McpServer.class);
+        this.baseUrl = "http://localhost:8080";
+    }
+
+    @Nested
+    @DisplayName("Constructor Tests")
+    class GivenConstructor {
+        @Test
+        @DisplayName("Should throw exception when base URL is null or blank")
+        void shouldThrowExceptionWhenBaseUrlIsNullOrEmpty() {
+            // Null
+            var exception1 = catchThrowableOfType(IllegalArgumentException.class,
+                    () -> new McpController(null, objectSerializer, mcpServer));
+            assertThat(exception1).hasMessage("The base URL for MCP server cannot be blank.");
+
+            // Blank
+            var exception2 = catchThrowableOfType(IllegalArgumentException.class,
+                    () -> new McpController("", objectSerializer, mcpServer));
+            assertThat(exception2).hasMessage("The base URL for MCP server cannot be blank.");
+        }
+
+        @Test
+        @DisplayName("Should throw exception when serializer is null")
+        void shouldThrowExceptionWhenSerializerIsNull() {
+            var exception = catchThrowableOfType(IllegalArgumentException.class,
+                    () -> new McpController(baseUrl, null, mcpServer));
+            assertThat(exception).hasMessage("The json serializer cannot be null.");
+        }
+
+        @Test
+        @DisplayName("Should throw exception when mcpServer is null")
+        void shouldThrowExceptionWhenMcpServerIsNull() {
+            var exception = catchThrowableOfType(IllegalArgumentException.class,
+                    () -> new McpController(baseUrl, objectSerializer, null));
+            assertThat(exception).hasMessage("The MCP server cannot be null.");
+        }
+    }
+}