feat(vertex-ai-gemini): enhance jsonToStruct to support JSON arrays

- Improve the jsonToStruct method in VertexAiGeminiChatModel to handle JSON arrays
  in addition to JSON objects. When a JSON array is detected, it's now properly
  converted to a Protobuf Struct with an items field containing the array elements.
- Added test

Resolves #2647 , #2849

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>

Author: tzolov

models/spring-ai-vertex-ai-gemini/src/main/java/org/springframework/ai/vertexai/gemini/VertexAiGeminiChatModel.java

@@ -16,14 +16,14 @@
 
 package org.springframework.ai.vertexai.gemini;
 
-import com.google.cloud.vertexai.api.Tool.GoogleSearch;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
 
 import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.annotation.JsonInclude.Include;
+import com.fasterxml.jackson.databind.JsonNode;
 import com.google.cloud.vertexai.VertexAI;
 import com.google.cloud.vertexai.api.Candidate;
 import com.google.cloud.vertexai.api.Candidate.FinishReason;
@@ -33,15 +33,16 @@
 import com.google.cloud.vertexai.api.FunctionResponse;
 import com.google.cloud.vertexai.api.GenerateContentResponse;
 import com.google.cloud.vertexai.api.GenerationConfig;
-import com.google.cloud.vertexai.api.GoogleSearchRetrieval;
 import com.google.cloud.vertexai.api.Part;
 import com.google.cloud.vertexai.api.SafetySetting;
 import com.google.cloud.vertexai.api.Schema;
 import com.google.cloud.vertexai.api.Tool;
+import com.google.cloud.vertexai.api.Tool.GoogleSearch;
 import com.google.cloud.vertexai.generativeai.GenerativeModel;
 import com.google.cloud.vertexai.generativeai.PartMaker;
 import com.google.cloud.vertexai.generativeai.ResponseStream;
 import com.google.protobuf.Struct;
+import com.google.protobuf.Value;
 import com.google.protobuf.util.JsonFormat;
 import io.micrometer.observation.Observation;
 import io.micrometer.observation.ObservationRegistry;
@@ -226,7 +227,8 @@ public VertexAiGeminiChatModel(VertexAI vertexAI, VertexAiGeminiChatOptions defa
 		this.observationRegistry = observationRegistry;
 		this.toolExecutionEligibilityPredicate = toolExecutionEligibilityPredicate;
 
-		// Wrap the provided tool calling manager in a VertexToolCallingManager to ensure
+		// Wrap the provided tool calling manager in a VertexToolCallingManager to
+		// ensure
 		// compatibility with Vertex AI's OpenAPI schema format.
 		if (toolCallingManager instanceof VertexToolCallingManager) {
 			this.toolCallingManager = toolCallingManager;
@@ -334,8 +336,34 @@ private static String structToJson(Struct struct) {
 
 	private static Struct jsonToStruct(String json) {
 		try {
-			var structBuilder = Struct.newBuilder();
-			JsonFormat.parser().ignoringUnknownFields().merge(json, structBuilder);
+			JsonNode rootNode = ModelOptionsUtils.OBJECT_MAPPER.readTree(json);
+
+			Struct.Builder structBuilder = Struct.newBuilder();
+
+			if (rootNode.isArray()) {
+				// Handle JSON array
+				List<Value> values = new ArrayList<>();
+
+				for (JsonNode element : rootNode) {
+					String elementJson = element.toString();
+					Struct.Builder elementBuilder = Struct.newBuilder();
+					JsonFormat.parser().ignoringUnknownFields().merge(elementJson, elementBuilder);
+
+					// Add each parsed object as a value in an array field
+					values.add(Value.newBuilder().setStructValue(elementBuilder.build()).build());
+				}
+
+				// Add the array to the main struct with a field name like "items"
+				structBuilder.putFields("items",
+						Value.newBuilder()
+							.setListValue(com.google.protobuf.ListValue.newBuilder().addAllValues(values).build())
+							.build());
+			}
+			else {
+				// Original behavior for single JSON object
+				JsonFormat.parser().ignoringUnknownFields().merge(json, structBuilder);
+			}
+
 			return structBuilder.build();
 		}
 		catch (Exception e) {

models/spring-ai-vertex-ai-gemini/src/test/java/org/springframework/ai/vertexai/gemini/VertexAiGeminiChatModelIT.java

@@ -25,11 +25,13 @@
 
 import com.google.cloud.vertexai.Transport;
 import com.google.cloud.vertexai.VertexAI;
+import io.micrometer.observation.ObservationRegistry;
 import org.jetbrains.annotations.NotNull;
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.condition.EnabledIfEnvironmentVariable;
 
+import org.springframework.ai.chat.client.ChatClient;
 import org.springframework.ai.chat.messages.AssistantMessage;
 import org.springframework.ai.chat.messages.Message;
 import org.springframework.ai.chat.messages.UserMessage;
@@ -42,6 +44,8 @@
 import org.springframework.ai.converter.BeanOutputConverter;
 import org.springframework.ai.converter.ListOutputConverter;
 import org.springframework.ai.converter.MapOutputConverter;
+import org.springframework.ai.model.tool.ToolCallingManager;
+import org.springframework.ai.tool.annotation.Tool;
 import org.springframework.ai.vertexai.gemini.VertexAiGeminiChatModel.ChatModel;
 import org.springframework.ai.vertexai.gemini.common.VertexAiGeminiSafetySetting;
 import org.springframework.beans.factory.annotation.Autowired;
@@ -293,6 +297,70 @@ void multiModalityPdfTest() throws IOException {
 		assertThat(response.getResult().getOutput().getText()).containsAnyOf("Spring AI", "portable API");
 	}
 
+	/**
+	 * Helper method to create a VertexAI instance for tests
+	 */
+	private VertexAI vertexAiApi() {
+		String projectId = System.getenv("VERTEX_AI_GEMINI_PROJECT_ID");
+		String location = System.getenv("VERTEX_AI_GEMINI_LOCATION");
+		return new VertexAI.Builder().setProjectId(projectId)
+			.setLocation(location)
+			.setTransport(Transport.REST)
+			.build();
+	}
+
+	@Test
+	void jsonArrayToolCallingTest() {
+		// Test for the improved jsonToStruct method that handles JSON arrays in tool
+		// calling
+
+		ToolCallingManager toolCallingManager = ToolCallingManager.builder()
+			.observationRegistry(ObservationRegistry.NOOP)
+			.build();
+
+		VertexAiGeminiChatModel chatModelWithTools = VertexAiGeminiChatModel.builder()
+			.vertexAI(vertexAiApi())
+			.toolCallingManager(toolCallingManager)
+			.defaultOptions(VertexAiGeminiChatOptions.builder()
+				.model(VertexAiGeminiChatModel.ChatModel.GEMINI_2_0_FLASH)
+				.temperature(0.1)
+				.build())
+			.build();
+
+		ChatClient chatClient = ChatClient.builder(chatModelWithTools).build();
+
+		// Create a prompt that will trigger the tool call with a specific request that
+		// should invoke the tool
+		String response = chatClient.prompt()
+			.tools(new ScientistTools())
+			.user("List 3 famous scientists and their discoveries. Make sure to use the tool to get this information.")
+			.call()
+			.content();
+
+		assertThat(response).isNotEmpty();
+
+		assertThat(response).satisfiesAnyOf(content -> assertThat(content).contains("Einstein"),
+				content -> assertThat(content).contains("Newton"), content -> assertThat(content).contains("Curie"));
+
+	}
+
+	/**
+	 * Tool class that returns a JSON array to test the jsonToStruct method's ability to
+	 * handle JSON arrays. This specifically tests the PR changes that improve the
+	 * jsonToStruct method to handle JSON arrays in addition to JSON objects.
+	 */
+	public static class ScientistTools {
+
+		@Tool(description = "Get information about famous scientists and their discoveries")
+		public List<Map<String, String>> getScientists() {
+			// Return a JSON array with scientist information
+			return List.of(Map.of("name", "Albert Einstein", "discovery", "Theory of Relativity"),
+					Map.of("name", "Isaac Newton", "discovery", "Laws of Motion"),
+					Map.of("name", "Marie Curie", "discovery", "Radioactivity"));
+		}
+
+	}
+
 	record ActorsFilmsRecord(String actor, List<String> movies) {
 
 	}

models/spring-ai-vertex-ai-gemini/src/test/java/org/springframework/ai/vertexai/gemini/tool/VertexAiGeminiChatModelToolCallingIT.java

@@ -126,7 +126,7 @@ public void functionCallTestInferredOpenApiSchema() {
 
 		assertThat(chatResponse.getMetadata()).isNotNull();
 		assertThat(chatResponse.getMetadata().getUsage()).isNotNull();
-		assertThat(chatResponse.getMetadata().getUsage().getTotalTokens()).isGreaterThan(150).isLessThan(310);
+		assertThat(chatResponse.getMetadata().getUsage().getTotalTokens()).isGreaterThan(150).isLessThan(330);
 
 		ChatResponse response2 = this.chatModel
 			.call(new Prompt("What is the payment status for transaction 696?", promptOptions));
@@ -201,7 +201,7 @@ public void functionCallUsageTestInferredOpenApiSchemaStream() {
 		assertThat(chatResponse).isNotNull();
 		assertThat(chatResponse.getMetadata()).isNotNull();
 		assertThat(chatResponse.getMetadata().getUsage()).isNotNull();
-		assertThat(chatResponse.getMetadata().getUsage().getTotalTokens()).isGreaterThan(150).isLessThan(310);
+		assertThat(chatResponse.getMetadata().getUsage().getTotalTokens()).isGreaterThan(150).isLessThan(330);
 
 	}
 

spring-ai-model/src/main/java/org/springframework/ai/converter/ListOutputConverter.java

@@ -31,6 +31,10 @@
  */
 public class ListOutputConverter extends AbstractConversionServiceOutputConverter<List<String>> {
 
+	public ListOutputConverter() {
+		this(new DefaultConversionService());
+	}
+
 	public ListOutputConverter(DefaultConversionService defaultConversionService) {
 		super(defaultConversionService);
 	}