feat: Add support for Consumer and Supplier function callbacks

- Add support for Java Consumer and Supplier functional interfaces in function callbacks
- Handle void type inputs and outputs in function callbacks
- Add test cases for void responses, Consumer callbacks, and Supplier callbacks
- Update ModelOptionsUtils to properly handle void type schemas

Resolves #1718 and #1277

Author: tzolov

spring-ai-core/src/main/java/org/springframework/ai/model/ModelOptionsUtils.java

@@ -51,6 +51,7 @@
 import org.springframework.beans.BeanWrapper;
 import org.springframework.beans.BeanWrapperImpl;
 import org.springframework.util.Assert;
+import org.springframework.util.ClassUtils;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.ObjectUtils;
 
@@ -358,8 +359,13 @@ public static String getJsonSchema(Class<?> clazz, boolean toUpperCaseTypeValues
 		}
 
 		ObjectNode node = SCHEMA_GENERATOR_CACHE.get().generateSchema(clazz);
-		if (toUpperCaseTypeValues) { // Required for OpenAPI 3.0 (at least Vertex AI
-			// version of it).
+
+		if (ClassUtils.isVoidType(clazz) && node.get("properties") == null) {
+			node.putObject("properties");
+		}
+
+		// Required for OpenAPI 3.0 (at least Vertex AI version of it).
+		if (toUpperCaseTypeValues) {
 			toUpperCaseTypeValues(node);
 		}
 

spring-ai-core/src/main/java/org/springframework/ai/model/function/FunctionCallbackContext.java

@@ -17,7 +17,9 @@
 package org.springframework.ai.model.function;
 
 import java.util.function.BiFunction;
+import java.util.function.Consumer;
 import java.util.function.Function;
+import java.util.function.Supplier;
 
 import com.fasterxml.jackson.annotation.JsonClassDescription;
 import kotlin.jvm.functions.Function1;
@@ -129,6 +131,22 @@ else if (KotlinDelegate.isKotlinBiFunction(functionType.toClass())) {
 				.withInputType(functionInputClass)
 				.build();
 		}
+		if (bean instanceof Consumer<?> consumer) {
+			return FunctionCallbackWrapper.builder(consumer)
+				.withName(beanName)
+				.withSchemaType(this.schemaType)
+				.withDescription(functionDescription)
+				.withInputType(functionInputClass)
+				.build();
+		}
+		if (bean instanceof Supplier<?> supplier) {
+			return FunctionCallbackWrapper.builder(supplier)
+				.withName(beanName)
+				.withSchemaType(this.schemaType)
+				.withDescription(functionDescription)
+				.withInputType(functionInputClass)
+				.build();
+		}
 		else if (bean instanceof BiFunction<?, ?, ?>) {
 			return FunctionCallbackWrapper.builder((BiFunction<?, ToolContext, ?>) bean)
 				.withName(beanName)

spring-ai-core/src/main/java/org/springframework/ai/model/function/FunctionCallbackWrapper.java

@@ -17,7 +17,9 @@
 package org.springframework.ai.model.function;
 
 import java.util.function.BiFunction;
+import java.util.function.Consumer;
 import java.util.function.Function;
+import java.util.function.Supplier;
 
 import com.fasterxml.jackson.databind.DeserializationFeature;
 import com.fasterxml.jackson.databind.ObjectMapper;
@@ -59,6 +61,19 @@ public static <I, O> Builder<I, O> builder(Function<I, O> function) {
 		return new Builder<>(function);
 	}
 
+	public static <Void, O> Builder<Void, O> builder(Supplier<O> supplier) {
+		Function<Void, O> function = (input) -> supplier.get();
+		return new Builder<>(function);
+	}
+
+	public static <I, Void> Builder<I, Void> builder(Consumer<I> consumer) {
+		Function<I, Void> function = (input) -> {
+			consumer.accept(input);
+			return null;
+		};
+		return new Builder<>(function);
+	}
+
 	@Override
 	public O apply(I input, ToolContext context) {
 		return this.biFunction.apply(input, context);

spring-ai-core/src/main/java/org/springframework/ai/model/function/TypeResolverHelper.java

@@ -20,7 +20,9 @@
 import java.lang.reflect.Modifier;
 import java.util.Arrays;
 import java.util.function.BiFunction;
+import java.util.function.Consumer;
 import java.util.function.Function;
+import java.util.function.Supplier;
 
 import kotlin.jvm.functions.Function1;
 import kotlin.jvm.functions.Function2;
@@ -189,6 +191,12 @@ public static ResolvableType getFunctionArgumentType(ResolvableType functionType
 		else if (BiFunction.class.isAssignableFrom(resolvableClass)) {
 			functionArgumentResolvableType = functionType.as(BiFunction.class);
 		}
+		else if (Supplier.class.isAssignableFrom(resolvableClass)) {
+			return ResolvableType.forClass(Void.class);
+		}
+		else if (Consumer.class.isAssignableFrom(resolvableClass)) {
+			functionArgumentResolvableType = functionType.as(Consumer.class);
+		}
 		else if (KotlinDetector.isKotlinPresent()) {
 			if (KotlinDelegate.isKotlinFunction(resolvableClass)) {
 				functionArgumentResolvableType = KotlinDelegate.adaptToKotlinFunctionType(functionType);