feat(spring-ai): Introduce FunctionCallback.Builder

- Introduce FunctionCallback.Builder interface for improved builder pattern.
- Add support for generic type parameters via ResolvableType.
  Enhance function callbacks with generic type support.
- Move CustomizedTypeReference to ModelOptionsUtils for broader reuse.
- Deprecate old FunctionCallbackWrapper.Builder in favor of DefaultFunctionCallbackBuilder.
- Add JSON schema generation support for ResolvableType.

Resolves #1731

Author: tzolov

spring-ai-core/src/main/java/org/springframework/ai/converter/BeanOutputConverter.java

@@ -16,7 +16,6 @@
 
 package org.springframework.ai.converter;
 
-import java.lang.reflect.Type;
 import java.util.Objects;
 
 import com.fasterxml.jackson.core.JsonProcessingException;
@@ -37,6 +36,7 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import org.springframework.ai.model.ModelOptionsUtils.CustomizedTypeReference;
 import org.springframework.ai.util.JacksonUtils;
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.lang.NonNull;
@@ -94,7 +94,7 @@ public BeanOutputConverter(Class<T> clazz, ObjectMapper objectMapper) {
 	 * @param typeRef The target class type reference.
 	 */
 	public BeanOutputConverter(ParameterizedTypeReference<T> typeRef) {
-		this(new CustomizedTypeReference<>(typeRef), null);
+		this(CustomizedTypeReference.forType(typeRef), null);
 	}
 
 	/**
@@ -105,7 +105,7 @@ public BeanOutputConverter(ParameterizedTypeReference<T> typeRef) {
 	 * @param objectMapper Custom object mapper for JSON operations. endings.
 	 */
 	public BeanOutputConverter(ParameterizedTypeReference<T> typeRef, ObjectMapper objectMapper) {
-		this(new CustomizedTypeReference<>(typeRef), objectMapper);
+		this(CustomizedTypeReference.forType(typeRef), objectMapper);
 	}
 
 	/**
@@ -220,19 +220,4 @@ public String getJsonSchema() {
 		return this.jsonSchema;
 	}
 
-	private static class CustomizedTypeReference<T> extends TypeReference<T> {
-
-		private final Type type;
-
-		CustomizedTypeReference(ParameterizedTypeReference<T> typeRef) {
-			this.type = typeRef.getType();
-		}
-
-		@Override
-		public Type getType() {
-			return this.type;
-		}
-
-	}
-
 }

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

@@ -18,6 +18,7 @@
 
 import java.beans.PropertyDescriptor;
 import java.lang.reflect.Field;
+import java.lang.reflect.Type;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
@@ -50,6 +51,8 @@
 import org.springframework.ai.util.JacksonUtils;
 import org.springframework.beans.BeanWrapper;
 import org.springframework.beans.BeanWrapperImpl;
+import org.springframework.core.ParameterizedTypeReference;
+import org.springframework.core.ResolvableType;
 import org.springframework.util.Assert;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.ObjectUtils;
@@ -366,6 +369,41 @@ public static String getJsonSchema(Class<?> clazz, boolean toUpperCaseTypeValues
 		return node.toPrettyString();
 	}
 
+	/**
+	 * Generates JSON Schema (version 2020_12) for the given class.
+	 * @param clazz the class to generate JSON Schema for.
+	 * @param toUpperCaseTypeValues if true, the type values are converted to upper case.
+	 * @return the generated JSON Schema as a String.
+	 */
+	public static String getJsonSchema(ResolvableType inputType, boolean toUpperCaseTypeValues) {
+
+		if (SCHEMA_GENERATOR_CACHE.get() == null) {
+
+			JacksonModule jacksonModule = new JacksonModule(JacksonOption.RESPECT_JSONPROPERTY_REQUIRED);
+			Swagger2Module swaggerModule = new Swagger2Module();
+
+			SchemaGeneratorConfigBuilder configBuilder = new SchemaGeneratorConfigBuilder(SchemaVersion.DRAFT_2020_12,
+					OptionPreset.PLAIN_JSON)
+				.with(Option.EXTRA_OPEN_API_FORMAT_VALUES)
+				.with(Option.PLAIN_DEFINITION_KEYS)
+				.with(swaggerModule)
+				.with(jacksonModule);
+
+			SchemaGeneratorConfig config = configBuilder.build();
+			SchemaGenerator generator = new SchemaGenerator(config);
+			SCHEMA_GENERATOR_CACHE.compareAndSet(null, generator);
+		}
+
+		ObjectNode node = SCHEMA_GENERATOR_CACHE.get()
+			.generateSchema(CustomizedTypeReference.forType(inputType).getType());
+		if (toUpperCaseTypeValues) { // Required for OpenAPI 3.0 (at least Vertex AI
+			// version of it).
+			toUpperCaseTypeValues(node);
+		}
+
+		return node.toPrettyString();
+	}
+
 	public static void toUpperCaseTypeValues(ObjectNode node) {
 		if (node == null) {
 			return;
@@ -405,4 +443,27 @@ public static <T> T mergeOption(T runtimeValue, T defaultValue) {
 		return ObjectUtils.isEmpty(runtimeValue) ? defaultValue : runtimeValue;
 	}
 
+	public static class CustomizedTypeReference<T> extends TypeReference<T> {
+
+		private final Type type;
+
+		public CustomizedTypeReference(ParameterizedTypeReference<T> typeRef) {
+			this.type = typeRef.getType();
+		}
+
+		@Override
+		public Type getType() {
+			return this.type;
+		}
+
+		public static <T> CustomizedTypeReference<T> forType(ParameterizedTypeReference<T> typeRef) {
+			return new CustomizedTypeReference<>(typeRef);
+		}
+
+		public static <T> CustomizedTypeReference<T> forType(ResolvableType resolvableType) {
+			return new CustomizedTypeReference<>(ParameterizedTypeReference.forType(resolvableType.getType()));
+		}
+
+	}
+
 }

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

@@ -24,6 +24,8 @@
 import com.fasterxml.jackson.databind.ObjectMapper;
 
 import org.springframework.ai.chat.model.ToolContext;
+import org.springframework.ai.model.ModelOptionsUtils.CustomizedTypeReference;
+import org.springframework.core.ResolvableType;
 import org.springframework.util.Assert;
 
 /**
@@ -47,7 +49,7 @@ abstract class AbstractFunctionCallback<I, O> implements BiFunction<I, ToolConte
 
 	private final String description;
 
-	private final Class<I> inputType;
+	private final ResolvableType inputType;
 
 	private final String inputTypeSchema;
 
@@ -72,6 +74,26 @@ abstract class AbstractFunctionCallback<I, O> implements BiFunction<I, ToolConte
 	 */
 	protected AbstractFunctionCallback(String name, String description, String inputTypeSchema, Class<I> inputType,
 			Function<O, String> responseConverter, ObjectMapper objectMapper) {
+		this(name, description, inputTypeSchema, ResolvableType.forClass(inputType), responseConverter, objectMapper);
+	}
+
+	/**
+	 * Constructs a new {@link AbstractFunctionCallback} with the given name, description,
+	 * input type and default object mapper.
+	 * @param name Function name. Should be unique within the ChatModel's function
+	 * registry.
+	 * @param description Function description. Used as a "system prompt" by the model to
+	 * decide if the function should be called.
+	 * @param inputTypeSchema Used to compute, the argument's Schema (such as JSON Schema
+	 * or OpenAPI Schema)required by the Model's function calling protocol.
+	 * @param inputType Used to compute, the argument's JSON schema required by the
+	 * Model's function calling protocol.
+	 * @param responseConverter Used to convert the function's output type to a string.
+	 * @param objectMapper Used to convert the function's input and output types to and
+	 * from JSON.
+	 */
+	protected AbstractFunctionCallback(String name, String description, String inputTypeSchema,
+			ResolvableType inputType, Function<O, String> responseConverter, ObjectMapper objectMapper) {
 		Assert.notNull(name, "Name must not be null");
 		Assert.notNull(description, "Description must not be null");
 		Assert.notNull(inputType, "InputType must not be null");
@@ -116,9 +138,9 @@ public String call(String functionArguments) {
 		return this.andThen(this.responseConverter).apply(request, null);
 	}
 
-	private <T> T fromJson(String json, Class<T> targetClass) {
+	private <T> T fromJson(String json, ResolvableType targetType) {
 		try {
-			return this.objectMapper.readValue(json, targetClass);
+			return this.objectMapper.readValue(json, CustomizedTypeReference.forType(targetType));
 		}
 		catch (JsonProcessingException e) {
 			throw new RuntimeException(e);