[FLINK-AGENTS] Fix Java agents failing to connect to MCP servers without prompt support (#538)

integrations/mcp/src/main/java/org/apache/flink/agents/integrations/mcp/MCPServer.java

@@ -257,6 +257,17 @@ private void validateHttpUrl() {
         }
     }
 
+    /**
+     * Check if the MCP server supports prompts based on its declared capabilities.
+     *
+     * @return true if the server declared prompt capabilities during initialization
+     */
+    public boolean supportsPrompts() {
+        McpSyncClient mcpClient = getClient();
+        McpSchema.ServerCapabilities caps = mcpClient.getServerCapabilities();
+        return caps != null && caps.prompts() != null;
+    }
+
     /**
      * List available tools from the MCP server.
      *

integrations/mcp/src/test/java/org/apache/flink/agents/integrations/mcp/MCPServerTest.java

@@ -243,4 +243,16 @@ void testClose() {
         server.close();
         server.close(); // Calling twice should be safe
     }
+
+    @Test
+    @DisabledOnJre(JRE.JAVA_11)
+    @DisplayName("supportsPrompts method exists and is callable via reflection")
+    void testSupportsPromptsMethodExists() throws Exception {
+        MCPServer server = new MCPServer(DEFAULT_ENDPOINT);
+
+        // Verify the method exists (AgentPlan calls it via reflection)
+        java.lang.reflect.Method method = server.getClass().getMethod("supportsPrompts");
+        assertThat(method).isNotNull();
+        assertThat(method.getReturnType()).isEqualTo(boolean.class);
+    }
 }

plan/src/main/java/org/apache/flink/agents/plan/AgentPlan.java

@@ -432,18 +432,22 @@ private void extractJavaMCPServer(Method method) throws Exception {
                     JavaSerializableResourceProvider.createResourceProvider(toolName, TOOL, tool));
         }
 
-        // Call listPrompts() via reflection
-        Method listPromptsMethod = mcpServer.getClass().getMethod("listPrompts");
-        @SuppressWarnings("unchecked")
-        Iterable<? extends SerializableResource> prompts =
-                (Iterable<? extends SerializableResource>) listPromptsMethod.invoke(mcpServer);
-
-        for (SerializableResource prompt : prompts) {
-            Method getNameMethod = prompt.getClass().getMethod("getName");
-            String promptName = (String) getNameMethod.invoke(prompt);
-            addResourceProvider(
-                    JavaSerializableResourceProvider.createResourceProvider(
-                            promptName, PROMPT, prompt));
+        // Call listPrompts() only if the server supports prompts (optional per MCP spec).
+        // MCP servers like AgentCore Gateway only support tools, not prompts.
+        Method supportsPromptsMethod = mcpServer.getClass().getMethod("supportsPrompts");
+        if ((boolean) supportsPromptsMethod.invoke(mcpServer)) {
+            Method listPromptsMethod = mcpServer.getClass().getMethod("listPrompts");
+            @SuppressWarnings("unchecked")
+            Iterable<? extends SerializableResource> prompts =
+                    (Iterable<? extends SerializableResource>) listPromptsMethod.invoke(mcpServer);
+
+            for (SerializableResource prompt : prompts) {
+                Method getNameMethod = prompt.getClass().getMethod("getName");
+                String promptName = (String) getNameMethod.invoke(prompt);
+                addResourceProvider(
+                        JavaSerializableResourceProvider.createResourceProvider(
+                                promptName, PROMPT, prompt));
+            }
         }
 
         // Call close() via reflection