feat: Add usage metadata to LLM Response model

It contains the number of tokens used by the model. This is in line with Python ADK and fixes #212.

PiperOrigin-RevId: 788041782

Author: google-genai-bot

core/src/main/java/com/google/adk/models/LlmResponse.java

@@ -28,6 +28,7 @@
 import com.google.genai.types.FinishReason;
 import com.google.genai.types.GenerateContentResponse;
 import com.google.genai.types.GenerateContentResponsePromptFeedback;
+import com.google.genai.types.GenerateContentResponseUsageMetadata;
 import com.google.genai.types.GroundingMetadata;
 import java.util.List;
 import java.util.Optional;
@@ -89,6 +90,10 @@ public abstract class LlmResponse extends JsonBaseModel {
   @JsonProperty("interrupted")
   public abstract Optional<Boolean> interrupted();
 
+  /** Usage metadata about the response(s). */
+  @JsonProperty("usageMetadata")
+  public abstract Optional<GenerateContentResponseUsageMetadata> usageMetadata();
+
   public abstract Builder toBuilder();
 
   /** Builder for constructing {@link LlmResponse} instances. */
@@ -134,6 +139,13 @@ static LlmResponse.Builder jacksonBuilder() {
 
     public abstract Builder errorMessage(Optional<String> errorMessage);
 
+    @JsonProperty("usageMetadata")
+    public abstract Builder usageMetadata(
+        @Nullable GenerateContentResponseUsageMetadata usageMetadata);
+
+    public abstract Builder usageMetadata(
+        Optional<GenerateContentResponseUsageMetadata> usageMetadata);
+
     @CanIgnoreReturnValue
     public final Builder response(GenerateContentResponse response) {
       Optional<List<Candidate>> candidatesOpt = response.candidates();
@@ -160,6 +172,7 @@ public final Builder response(GenerateContentResponse response) {
           this.errorMessage("Unknown error.");
         }
       }
+      this.usageMetadata(response.usageMetadata());
       return this;
     }
 

core/src/test/java/com/google/adk/models/LlmResponseTest.java

@@ -26,6 +26,7 @@
 import com.google.genai.types.Content;
 import com.google.genai.types.FinishReason;
 import com.google.genai.types.FunctionCall;
+import com.google.genai.types.GenerateContentResponseUsageMetadata;
 import com.google.genai.types.Part;
 import java.util.Optional;
 import org.junit.Before;
@@ -61,6 +62,12 @@ private Content createSampleFunctionCallContent(String functionName) {
   public void testSerializationAndDeserialization_allFieldsPresent()
       throws JsonProcessingException {
     Content sampleContent = createSampleContent("Hello, world!");
+    GenerateContentResponseUsageMetadata usageMetadata =
+        GenerateContentResponseUsageMetadata.builder()
+            .promptTokenCount(10)
+            .candidatesTokenCount(20)
+            .totalTokenCount(30)
+            .build();
     LlmResponse originalResponse =
         LlmResponse.builder()
             .content(sampleContent)
@@ -69,6 +76,7 @@ public void testSerializationAndDeserialization_allFieldsPresent()
             .errorCode(new FinishReason("ERR_123"))
             .errorMessage(Optional.of("An error occurred."))
             .interrupted(Optional.of(true))
+            .usageMetadata(usageMetadata)
             .build();
 
     String json = originalResponse.toJson();
@@ -83,6 +91,10 @@ public void testSerializationAndDeserialization_allFieldsPresent()
     assertThat(jsonNode.get("errorCode").asText()).isEqualTo("ERR_123");
     assertThat(jsonNode.get("errorMessage").asText()).isEqualTo("An error occurred.");
     assertThat(jsonNode.get("interrupted").asBoolean()).isTrue();
+    assertThat(jsonNode.has("usageMetadata")).isTrue();
+    assertThat(jsonNode.get("usageMetadata").get("promptTokenCount").asInt()).isEqualTo(10);
+    assertThat(jsonNode.get("usageMetadata").get("candidatesTokenCount").asInt()).isEqualTo(20);
+    assertThat(jsonNode.get("usageMetadata").get("totalTokenCount").asInt()).isEqualTo(30);
 
     LlmResponse deserializedResponse = LlmResponse.fromJsonString(json, LlmResponse.class);
 
@@ -93,6 +105,7 @@ public void testSerializationAndDeserialization_allFieldsPresent()
     assertThat(deserializedResponse.errorCode()).hasValue(new FinishReason("ERR_123"));
     assertThat(deserializedResponse.errorMessage()).hasValue("An error occurred.");
     assertThat(deserializedResponse.interrupted()).hasValue(true);
+    assertThat(deserializedResponse.usageMetadata()).hasValue(usageMetadata);
   }
 
   @Test
@@ -108,6 +121,7 @@ public void testSerializationAndDeserialization_optionalFieldsEmpty()
             .errorCode(Optional.empty())
             .errorMessage(Optional.empty())
             .interrupted(Optional.empty())
+            .usageMetadata(Optional.empty())
             .build();
 
     String json = originalResponse.toJson();
@@ -122,6 +136,7 @@ public void testSerializationAndDeserialization_optionalFieldsEmpty()
     assertThat(jsonNode.has("errorCode")).isFalse();
     assertThat(jsonNode.has("errorMessage")).isFalse();
     assertThat(jsonNode.has("interrupted")).isFalse();
+    assertThat(jsonNode.has("usageMetadata")).isFalse();
 
     LlmResponse deserializedResponse = LlmResponse.fromJsonString(json, LlmResponse.class);
 
@@ -133,6 +148,7 @@ public void testSerializationAndDeserialization_optionalFieldsEmpty()
     assertThat(deserializedResponse.errorCode()).isEmpty();
     assertThat(deserializedResponse.errorMessage()).isEmpty();
     assertThat(deserializedResponse.interrupted()).isEmpty();
+    assertThat(deserializedResponse.usageMetadata()).isEmpty();
   }
 
   @Test
@@ -146,7 +162,8 @@ public void testDeserialization_optionalFieldsNullInJson() throws JsonProcessing
             + "\"turnComplete\": true,"
             + "\"errorCode\": null,"
             + "\"errorMessage\": null,"
-            + "\"interrupted\": null"
+            + "\"interrupted\": null,"
+            + "\"usageMetadata\": null"
             + "}";
 
     LlmResponse deserializedResponse = LlmResponse.fromJsonString(jsonWithNulls, LlmResponse.class);
@@ -160,6 +177,7 @@ public void testDeserialization_optionalFieldsNullInJson() throws JsonProcessing
     assertThat(deserializedResponse.errorCode()).isEmpty();
     assertThat(deserializedResponse.errorMessage()).isEmpty();
     assertThat(deserializedResponse.interrupted()).isEmpty();
+    assertThat(deserializedResponse.usageMetadata()).isEmpty();
   }
 
   @Test
@@ -185,6 +203,7 @@ public void testDeserialization_someOptionalFieldsMissingSomePresent()
     assertThat(jsonNode.get("errorCode").asText()).isEqualTo("FATAL_ERROR");
     assertThat(jsonNode.has("errorMessage")).isFalse();
     assertThat(jsonNode.has("interrupted")).isFalse();
+    assertThat(jsonNode.has("usageMetadata")).isFalse();
 
     LlmResponse deserializedResponse = LlmResponse.fromJsonString(json, LlmResponse.class);
     assertThat(deserializedResponse).isEqualTo(originalResponse);
@@ -197,5 +216,6 @@ public void testDeserialization_someOptionalFieldsMissingSomePresent()
     assertThat(deserializedResponse.errorCode()).hasValue(new FinishReason("FATAL_ERROR"));
     assertThat(deserializedResponse.errorMessage()).isEmpty();
     assertThat(deserializedResponse.interrupted()).isEmpty();
+    assertThat(deserializedResponse.usageMetadata()).isEmpty();
   }
 }