feat: automatically parse a java.lang.reflect.Method instance into a FunctionDeclaration when users pass it in as a Tool.

PiperOrigin-RevId: 756851696

Author: yyyu-google

examples/pom.xml

@@ -14,6 +14,22 @@
     <maven.compiler.target>1.8</maven.compiler.target>
     <google-genai.version>0.8.0-SNAPSHOT</google-genai.version><!-- {x-version-update:google-genai:current} -->
   </properties>
+  <build>
+    <pluginManagement>
+      <plugins>
+        <plugin>
+          <groupId>org.apache.maven.plugins</groupId>
+          <artifactId>maven-compiler-plugin</artifactId>
+          <version>3.14.0</version>
+          <configuration>
+            <compilerArgs>
+              <arg>-parameters</arg>
+            </compilerArgs>
+          </configuration>
+        </plugin>
+      </plugins>
+    </pluginManagement>
+  </build>
 
   <dependencies>
     <dependency>

examples/src/main/java/com/google/genai/examples/GenerateContentWithFunctionCall.java

@@ -40,52 +40,38 @@
 package com.google.genai.examples;
 
 import com.google.common.collect.ImmutableList;
-import com.google.common.collect.ImmutableMap;
 import com.google.genai.Client;
-import com.google.genai.types.FunctionDeclaration;
 import com.google.genai.types.GenerateContentConfig;
 import com.google.genai.types.GenerateContentResponse;
-import com.google.genai.types.Schema;
-import com.google.genai.types.Type;
+import com.google.genai.types.Tool;
+import java.lang.reflect.Method;
 
 /** An example of using the Unified Gen AI Java SDK to generate content with function calling. */
 public class GenerateContentWithFunctionCall {
-  public static void main(String[] args) {
+  public static String getCurrentWeather(String location, String unit) {
+    return "The weather in " + location + " is " + "very nice.";
+  }
+  public static void main(String[] args) throws NoSuchMethodException {
     // Instantiate the client using Gemini Developer API.
     Client client = new Client();
 
-    FunctionDeclaration functionDeclaration =
-        FunctionDeclaration.builder()
-            .name("get_current_weather")
-            .parameters(
-                Schema.builder()
-                    .type(Type.Known.OBJECT)
-                    .properties(
-                        ImmutableMap.of(
-                            "location",
-                            Schema.builder()
-                                .type(Type.Known.STRING)
-                                .description("The location to get the weather for.")
-                                .build(),
-                            "unit",
-                            Schema.builder()
-                                .type(Type.Known.STRING)
-                                .description("The unit to return the weather in, e.g. 'celsius'.")
-                                .build()))
-                    .required(ImmutableList.of("location", "unit"))
-                    .build())
-            .build();
+    Method method = GenerateContentWithFunctionCall.class.getMethod(
+        "getCurrentWeather", String.class, String.class);
 
     GenerateContentConfig config =
-        GenerateContentConfig.fromJson(
-            String.format(
-                "{\"tools\":[{\"functionDeclarations\":[%s]}]}", functionDeclaration.toJson()));
+        GenerateContentConfig.builder()
+            .tools(ImmutableList.of(
+                Tool.builder()
+                .functions(ImmutableList.of(method))
+                .build()
+            ))
+            .build();
 
     GenerateContentResponse response =
         client.models.generateContent(
             "gemini-2.0-flash-001", "What is the weather in Vancouver?", config);
 
-    // Gets the function calls from the response by the quick accessor method `functionCalls()`.
-    System.out.println("Response: " + response.functionCalls());
+    // to look into what arguments were passed to call the getCurrentWeather function.
+    System.out.println("Function call arguments: " + response.functionCalls());
   }
 }

pom.xml

@@ -256,6 +256,17 @@
           </executions>
         </plugin>
         <plugin>
+          <groupId>org.apache.maven.plugins</groupId>
+          <artifactId>maven-compiler-plugin</artifactId>
+          <version>3.14.0</version>
+          <configuration>
+            <compilerArgs>
+              <arg>-parameters</arg>
+            </compilerArgs>
+          </configuration>
+        </plugin>
+        <plugin>
+          <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-javadoc-plugin</artifactId>
           <version>3.6.3</version>
           <configuration>

src/main/java/com/google/genai/AfcUtil.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2025 Google LLC
+ *
+ * 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 com.google.genai;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import com.google.common.collect.ImmutableList;
+import com.google.genai.types.GenerateContentConfig;
+import com.google.genai.types.Tool;
+
+final class AfcUtil {
+
+  static GenerateContentConfig transformGenerateContentConfig(
+      ApiClient apiClient, GenerateContentConfig config) {
+    GenerateContentConfig transformedConfig;
+    if (config != null && config.tools().isPresent() && !config.tools().get().isEmpty()) {
+      ImmutableList<Tool> transformedTools =
+          config.tools().get().stream()
+              .map(tool -> Transformers.tTool(apiClient, tool))
+              .collect(toImmutableList());
+      ObjectNode configNode = JsonSerializable.objectMapper.valueToTree(config);
+      configNode.set("tools", JsonSerializable.objectMapper.valueToTree(transformedTools));
+      transformedConfig = JsonSerializable.fromJsonNode(configNode, GenerateContentConfig.class);
+    } else {
+      transformedConfig = config;
+    }
+    return transformedConfig;
+  }
+
+  private AfcUtil() {}
+}

src/main/java/com/google/genai/Models.java

@@ -4576,7 +4576,9 @@ public GenerateVideosOperation generateVideos(
    */
   public GenerateContentResponse generateContent(
       String model, List<Content> contents, GenerateContentConfig config) {
-    return privateGenerateContent(model, contents, config);
+    GenerateContentConfig transformedConfig =
+        AfcUtil.transformGenerateContentConfig(apiClient, config);
+    return privateGenerateContent(model, contents, transformedConfig);
   }
 
   /**
@@ -4591,8 +4593,7 @@ public GenerateContentResponse generateContent(
    */
   public GenerateContentResponse generateContent(
       String model, Content content, GenerateContentConfig config) {
-    return privateGenerateContent(
-        model, Transformers.tContents(this.apiClient, (Object) content), config);
+    return generateContent(model, Transformers.tContents(this.apiClient, (Object) content), config);
   }
 
   /**
@@ -4607,8 +4608,7 @@ public GenerateContentResponse generateContent(
    */
   public GenerateContentResponse generateContent(
       String model, String text, GenerateContentConfig config) {
-    return privateGenerateContent(
-        model, Transformers.tContents(this.apiClient, (Object) text), config);
+    return generateContent(model, Transformers.tContents(this.apiClient, (Object) text), config);
   }
 
   /**
@@ -4623,7 +4623,9 @@ public GenerateContentResponse generateContent(
    */
   public ResponseStream<GenerateContentResponse> generateContentStream(
       String model, List<Content> contents, GenerateContentConfig config) {
-    return privateGenerateContentStream(model, contents, config);
+    GenerateContentConfig transformedConfig =
+        AfcUtil.transformGenerateContentConfig(apiClient, config);
+    return privateGenerateContentStream(model, contents, transformedConfig);
   }
 
   /**
@@ -4638,7 +4640,7 @@ public ResponseStream<GenerateContentResponse> generateContentStream(
    */
   public ResponseStream<GenerateContentResponse> generateContentStream(
       String model, Content content, GenerateContentConfig config) {
-    return privateGenerateContentStream(
+    return generateContentStream(
         model, Transformers.tContents(this.apiClient, (Object) content), config);
   }
 
@@ -4654,7 +4656,7 @@ public ResponseStream<GenerateContentResponse> generateContentStream(
    */
   public ResponseStream<GenerateContentResponse> generateContentStream(
       String model, String text, GenerateContentConfig config) {
-    return privateGenerateContentStream(
+    return generateContentStream(
         model, Transformers.tContents(this.apiClient, (Object) text), config);
   }
 

src/main/java/com/google/genai/Transformers.java

@@ -20,15 +20,18 @@
 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.node.ArrayNode;
 import com.fasterxml.jackson.databind.node.JsonNodeFactory;
+import com.fasterxml.jackson.databind.node.ObjectNode;
 import com.google.common.collect.ImmutableList;
 import com.google.genai.types.Blob;
 import com.google.genai.types.Content;
+import com.google.genai.types.FunctionDeclaration;
 import com.google.genai.types.Part;
 import com.google.genai.types.PrebuiltVoiceConfig;
 import com.google.genai.types.Schema;
 import com.google.genai.types.SpeechConfig;
 import com.google.genai.types.Tool;
 import com.google.genai.types.VoiceConfig;
+import java.lang.reflect.Method;
 import java.util.ArrayList;
 import java.util.List;
 import org.jspecify.annotations.Nullable;
@@ -171,7 +174,12 @@ public static List<Tool> tTools(ApiClient apiClient, Object origin) {
     if (origin == null) {
       return null;
     } else if (origin instanceof List) {
-      return (List<Tool>) origin;
+      List<Tool> tools = (List<Tool>) origin;
+      List<Tool> transformedTools = new ArrayList<>();
+      for (Tool tool : tools) {
+        transformedTools.add(tTool(apiClient, tool));
+      }
+      return transformedTools;
     } else if (origin instanceof JsonNode) {
       return JsonSerializable.objectMapper.convertValue(
           (JsonNode) origin, new TypeReference<List<Tool>>() {});
@@ -185,10 +193,30 @@ public static Tool tTool(ApiClient apiClient, Object origin) {
     if (origin == null) {
       return null;
     } else if (origin instanceof Tool) {
-      return (Tool) origin;
+      Tool tool = (Tool) origin;
+      if (!tool.functions().isPresent()) {
+        return tool;
+      }
+      List<FunctionDeclaration> combinedFunctionDeclarations = new ArrayList<>();
+      for (Method method : tool.functions().get()) {
+        combinedFunctionDeclarations.add(FunctionDeclaration.fromMethod(method));
+      }
+      if (tool.functionDeclarations().isPresent()) {
+        combinedFunctionDeclarations.addAll(tool.functionDeclarations().get());
+      }
+      ObjectNode toolNode = JsonSerializable.objectMapper.valueToTree(tool);
+      toolNode.remove("functions");
+      toolNode.set(
+          "functionDeclarations",
+          JsonSerializable.objectMapper.valueToTree(combinedFunctionDeclarations));
+      return JsonSerializable.fromJsonNode(toolNode, Tool.class);
     } else if (origin instanceof JsonNode) {
-      return JsonSerializable.objectMapper.convertValue(
-          (JsonNode) origin, new TypeReference<Tool>() {});
+      // in case reflectMethods is present in the json node, call tTool to parse it and remove it
+      // from the json node.
+      return tTool(
+          apiClient,
+          JsonSerializable.objectMapper.convertValue(
+              (JsonNode) origin, new TypeReference<Tool>() {}));
     }
 
     throw new IllegalArgumentException("Unsupported tool type: " + origin.getClass());

src/main/java/com/google/genai/types/Tool.java

@@ -19,10 +19,12 @@
 package com.google.genai.types;
 
 import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
 import com.google.auto.value.AutoValue;
 import com.google.genai.JsonSerializable;
+import java.lang.reflect.Method;
 import java.util.List;
 import java.util.Optional;
 
@@ -62,6 +64,13 @@ public abstract class Tool extends JsonSerializable {
   @JsonProperty("googleMaps")
   public abstract Optional<GoogleMaps> googleMaps();
 
+  /**
+   * The java.lang.reflect.Method instance. If provided, it will to be parsed into a list of
+   * FunctionDeclaration instances, and be assigned to the functionDeclarations field.
+   */
+  @JsonIgnore
+  public abstract Optional<List<Method>> functions();
+
   /**
    * Optional. CodeExecution tool type. Enables the model to execute code as part of generation.
    * This field is only used by the Gemini Developer API services.
@@ -111,6 +120,9 @@ private static Builder create() {
     @JsonProperty("googleMaps")
     public abstract Builder googleMaps(GoogleMaps googleMaps);
 
+    @JsonIgnore
+    public abstract Builder functions(List<Method> functions);
+
     @JsonProperty("codeExecution")
     public abstract Builder codeExecution(ToolCodeExecution codeExecution);