feat(google-genai): add Gemini Text-to-Speech (TTS) implementation

This commit adds comprehensive Text-to-Speech support for Google GenAI (Gemini) with the following components: ## API Client Layer - GeminiTtsApi: Low-level REST client for Gemini TTS API - Support for single-speaker and multi-speaker (conversational) TTS - PCM audio format (s16le, 24kHz, mono) - Request/response POJOs with Jackson annotations - Convenience factory methods for simpler API usage ## Model Layer - GeminiTtsModel: Spring AI TextToSpeechModel implementation - GeminiTtsOptions: Builder-based configuration with runtime overrides - Support for 30+ voices across 24+ languages - Prompt-based style control (accent, pace, delivery) ## Spring Boot Integration - Auto-configuration with properties binding - Dedicated starter: spring-ai-starter-model-google-genai-tts - Configuration prefix: spring.ai.google.genai.tts - Conditional bean creation based on spring.ai.model.audio.speech property Signed-off-by: Alexandros Pappas <apappascs@gmail.com>

Author: apappascs

auto-configurations/models/spring-ai-autoconfigure-model-google-genai/src/main/java/org/springframework/ai/model/google/genai/autoconfigure/tts/GoogleGenAiTtsAutoConfiguration.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2023-2025 the original author or authors.
+ *
+ * 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 org.springframework.ai.model.google.genai.autoconfigure.tts;
+
+import org.springframework.ai.google.genai.tts.GeminiTtsModel;
+import org.springframework.ai.google.genai.tts.api.GeminiTtsApi;
+import org.springframework.ai.model.SpringAIModelProperties;
+import org.springframework.ai.model.SpringAIModels;
+import org.springframework.ai.retry.autoconfigure.SpringAiRetryAutoConfiguration;
+import org.springframework.boot.autoconfigure.AutoConfiguration;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.context.annotation.Bean;
+import org.springframework.core.retry.RetryTemplate;
+import org.springframework.util.Assert;
+import org.springframework.util.StringUtils;
+
+/**
+ * Auto-configuration for Google GenAI Text-to-Speech.
+ *
+ * @author Alexandros Pappas
+ * @since 1.1.0
+ */
+@AutoConfiguration(after = SpringAiRetryAutoConfiguration.class)
+@ConditionalOnClass({ GeminiTtsApi.class, GeminiTtsModel.class })
+@ConditionalOnProperty(name = SpringAIModelProperties.AUDIO_SPEECH_MODEL, havingValue = SpringAIModels.GOOGLE_GEN_AI,
+matchIfMissing = false)
+@EnableConfigurationProperties({ GoogleGenAiTtsProperties.class, GoogleGenAiTtsConnectionProperties.class })
+public class GoogleGenAiTtsAutoConfiguration {
+
+@Bean
+@ConditionalOnMissingBean
+public GeminiTtsApi geminiTtsApi(GoogleGenAiTtsConnectionProperties connectionProperties) {
+Assert.hasText(connectionProperties.getApiKey(), "Google GenAI API key must be set!");
+
+if (StringUtils.hasText(connectionProperties.getBaseUrl())) {
+return new GeminiTtsApi(connectionProperties.getApiKey(), connectionProperties.getBaseUrl());
+}
+
+return new GeminiTtsApi(connectionProperties.getApiKey());
+}
+
+@Bean
+@ConditionalOnMissingBean
+public GeminiTtsModel geminiTtsModel(GeminiTtsApi geminiTtsApi, GoogleGenAiTtsProperties ttsProperties,
+RetryTemplate retryTemplate) {
+
+return GeminiTtsModel.builder()
+.geminiTtsApi(geminiTtsApi)
+.defaultOptions(ttsProperties.getOptions())
+.retryTemplate(retryTemplate)
+.build();
+}
+
+}

auto-configurations/models/spring-ai-autoconfigure-model-google-genai/src/main/java/org/springframework/ai/model/google/genai/autoconfigure/tts/GoogleGenAiTtsConnectionProperties.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2023-2025 the original author or authors.
+ *
+ * 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 org.springframework.ai.model.google.genai.autoconfigure.tts;
+
+import org.springframework.boot.context.properties.ConfigurationProperties;
+
+/**
+ * Connection properties for Google GenAI TTS.
+ *
+ * @author Alexandros Pappas
+ * @since 1.1.0
+ */
+@ConfigurationProperties(GoogleGenAiTtsConnectionProperties.CONFIG_PREFIX)
+public class GoogleGenAiTtsConnectionProperties {
+
+public static final String CONFIG_PREFIX = "spring.ai.google.genai";
+
+/**
+ * Google GenAI API Key for TTS.
+ */
+private String apiKey;
+
+/**
+ * Base URL for the Google GenAI TTS API.
+ */
+private String baseUrl = "https://generativelanguage.googleapis.com";
+
+public String getApiKey() {
+return this.apiKey;
+}
+
+public void setApiKey(String apiKey) {
+this.apiKey = apiKey;
+}
+
+public String getBaseUrl() {
+return this.baseUrl;
+}
+
+public void setBaseUrl(String baseUrl) {
+this.baseUrl = baseUrl;
+}
+
+}

auto-configurations/models/spring-ai-autoconfigure-model-google-genai/src/main/java/org/springframework/ai/model/google/genai/autoconfigure/tts/GoogleGenAiTtsProperties.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2025-2025 the original author or authors.
+ *
+ * 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 org.springframework.ai.model.google.genai.autoconfigure.tts;
+
+import org.springframework.ai.google.genai.tts.GeminiTtsOptions;
+import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.boot.context.properties.NestedConfigurationProperty;
+
+/**
+ * Configuration properties for Google GenAI Text-to-Speech.
+ *
+ * @author Alexandros Pappas
+ * @since 1.1.0
+ */
+@ConfigurationProperties(GoogleGenAiTtsProperties.CONFIG_PREFIX)
+public class GoogleGenAiTtsProperties {
+
+public static final String CONFIG_PREFIX = "spring.ai.google.genai.tts";
+
+public static final String DEFAULT_MODEL = "gemini-2.5-flash-preview-tts";
+
+public static final String DEFAULT_VOICE = "Kore";
+
+/**
+ * Google GenAI TTS options.
+ */
+@NestedConfigurationProperty
+private final GeminiTtsOptions options = GeminiTtsOptions.builder()
+.model(DEFAULT_MODEL)
+.voice(DEFAULT_VOICE)
+.build();
+
+public GeminiTtsOptions getOptions() {
+return this.options;
+}
+
+}

auto-configurations/models/spring-ai-autoconfigure-model-google-genai/src/main/resources/META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports

@@ -16,3 +16,4 @@
 org.springframework.ai.model.google.genai.autoconfigure.chat.GoogleGenAiChatAutoConfiguration
 org.springframework.ai.model.google.genai.autoconfigure.embedding.GoogleGenAiEmbeddingConnectionAutoConfiguration
 org.springframework.ai.model.google.genai.autoconfigure.embedding.GoogleGenAiTextEmbeddingAutoConfiguration
+org.springframework.ai.model.google.genai.autoconfigure.tts.GoogleGenAiTtsAutoConfiguration

auto-configurations/models/spring-ai-autoconfigure-model-google-genai/src/test/java/org/springframework/ai/model/google/genai/autoconfigure/tts/GoogleGenAiTtsAutoConfigurationIT.java

@@ -0,0 +1,83 @@
+/*
+ * Copyright 2025-2025 the original author or authors.
+ *
+ * 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 org.springframework.ai.model.google.genai.autoconfigure.tts;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.EnabledIfEnvironmentVariable;
+
+import org.springframework.ai.google.genai.tts.GeminiTtsModel;
+import org.springframework.ai.utils.SpringAiTestAutoConfigurations;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Integration tests for the {@link GoogleGenAiTtsAutoConfiguration}.
+ *
+ * @author Alexandros Pappas
+ */
+@EnabledIfEnvironmentVariable(named = "GOOGLE_API_KEY", matches = ".*")
+public class GoogleGenAiTtsAutoConfigurationIT {
+
+private static final org.apache.commons.logging.Log logger = org.apache.commons.logging.LogFactory
+.getLog(GoogleGenAiTtsAutoConfigurationIT.class);
+
+private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
+.withPropertyValues("spring.ai.google.genai.api-key=" + System.getenv("GOOGLE_API_KEY"),
+"spring.ai.model.audio.speech=google-genai")
+.withConfiguration(SpringAiTestAutoConfigurations.of(GoogleGenAiTtsAutoConfiguration.class));
+
+@Test
+void ttsModelBeanCreation() {
+this.contextRunner.run(context -> {
+assertThat(context).hasSingleBean(GeminiTtsModel.class);
+GeminiTtsModel ttsModel = context.getBean(GeminiTtsModel.class);
+assertThat(ttsModel).isNotNull();
+});
+}
+
+@Test
+void ttsModelApiCall() {
+this.contextRunner.run(context -> {
+GeminiTtsModel ttsModel = context.getBean(GeminiTtsModel.class);
+byte[] response = ttsModel.call("Hello");
+
+assertThat(response).isNotNull();
+assertThat(response).isNotEmpty();
+// PCM audio should be substantial (24kHz * 2 bytes/sample * ~1 second)
+assertThat(response.length).isGreaterThan(1000);
+
+logger.debug("PCM audio response size: " + response.length + " bytes");
+});
+}
+
+@Test
+void ttsModelWithCustomVoice() {
+this.contextRunner
+.withPropertyValues("spring.ai.google.genai.tts.options.voice=Puck",
+"spring.ai.google.genai.tts.options.model=gemini-2.5-flash-preview-tts")
+.run(context -> {
+GeminiTtsModel ttsModel = context.getBean(GeminiTtsModel.class);
+byte[] response = ttsModel.call("Testing custom voice");
+
+assertThat(response).isNotNull();
+assertThat(response).isNotEmpty();
+assertThat(response.length).isGreaterThan(1000);
+});
+}
+
+}

auto-configurations/models/spring-ai-autoconfigure-model-google-genai/src/test/java/org/springframework/ai/model/google/genai/autoconfigure/tts/GoogleGenAiTtsPropertiesTests.java

@@ -0,0 +1,89 @@
+/*
+ * Copyright 2025-2025 the original author or authors.
+ *
+ * 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 org.springframework.ai.model.google.genai.autoconfigure.tts;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.context.annotation.Configuration;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Unit tests for Google GenAI TTS properties binding.
+ *
+ * @author Alexandros Pappas
+ */
+public class GoogleGenAiTtsPropertiesTests {
+
+private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
+.withUserConfiguration(PropertiesTestConfiguration.class);
+
+@Test
+void connectionPropertiesBinding() {
+this.contextRunner
+.withPropertyValues("spring.ai.google.genai.api-key=test-tts-key",
+"spring.ai.google.genai.base-url=https://test.api.google.com")
+.run(context -> {
+GoogleGenAiTtsConnectionProperties connectionProperties = context
+.getBean(GoogleGenAiTtsConnectionProperties.class);
+assertThat(connectionProperties.getApiKey()).isEqualTo("test-tts-key");
+assertThat(connectionProperties.getBaseUrl()).isEqualTo("https://test.api.google.com");
+});
+}
+
+@Test
+void ttsPropertiesBinding() {
+this.contextRunner
+.withPropertyValues("spring.ai.google.genai.tts.options.model=gemini-2.5-pro-preview-tts",
+"spring.ai.google.genai.tts.options.voice=Puck", "spring.ai.google.genai.tts.options.speed=1.2")
+.run(context -> {
+GoogleGenAiTtsProperties ttsProperties = context.getBean(GoogleGenAiTtsProperties.class);
+assertThat(ttsProperties.getOptions().getModel()).isEqualTo("gemini-2.5-pro-preview-tts");
+assertThat(ttsProperties.getOptions().getVoice()).isEqualTo("Puck");
+assertThat(ttsProperties.getOptions().getSpeed()).isEqualTo(1.2);
+});
+}
+
+@Test
+void ttsDefaultValuesBinding() {
+// Test that defaults are applied when not specified
+this.contextRunner.run(context -> {
+GoogleGenAiTtsProperties ttsProperties = context.getBean(GoogleGenAiTtsProperties.class);
+assertThat(ttsProperties.getOptions().getModel()).isEqualTo("gemini-2.5-flash-preview-tts");
+assertThat(ttsProperties.getOptions().getVoice()).isEqualTo("Kore");
+assertThat(ttsProperties.getOptions().getFormat()).isEqualTo("pcm");
+});
+}
+
+@Test
+void connectionDefaultBaseUrl() {
+this.contextRunner.withPropertyValues("spring.ai.google.genai.api-key=test-key").run(context -> {
+GoogleGenAiTtsConnectionProperties connectionProperties = context
+.getBean(GoogleGenAiTtsConnectionProperties.class);
+assertThat(connectionProperties.getBaseUrl()).isEqualTo("https://generativelanguage.googleapis.com");
+});
+}
+
+@Configuration
+@EnableConfigurationProperties({ GoogleGenAiTtsConnectionProperties.class, GoogleGenAiTtsProperties.class })
+static class PropertiesTestConfiguration {
+
+}
+
+}