Add support for BiFunction class type resolution in TypeResolverHelper

- Adds special handling for BiFunction class types
- Adds test cases to verify BiFunction class type resolution
- Removes deprecated AbstractFunctionCallSupport class
- Cleans up unused imports in FunctionCallback

Resolves #1576

Author: tzolov

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

@@ -15,8 +15,6 @@
  */
 package org.springframework.ai.model.function;
 
-import java.util.Map;
-
 import org.springframework.ai.chat.model.ToolContext;
 
 /**

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

@@ -130,7 +130,14 @@ public static Type getFunctionArgumentType(Type functionType, int argumentIndex)
 
 		// Resolves: https://github.com/spring-projects/spring-ai/issues/726
 		if (!(functionType instanceof ParameterizedType)) {
-			functionType = FunctionTypeUtils.discoverFunctionTypeFromClass(FunctionTypeUtils.getRawType(functionType));
+			Class<?> functionalClass = FunctionTypeUtils.getRawType(functionType);
+			// Resolves: https://github.com/spring-projects/spring-ai/issues/1576
+			if (BiFunction.class.isAssignableFrom(functionalClass)) {
+				functionType = TypeResolver.reify(BiFunction.class, (Class<BiFunction<?, ?, ?>>) functionalClass);
+			}
+			else {
+				functionType = FunctionTypeUtils.discoverFunctionTypeFromClass(functionalClass);
+			}
 		}
 
 		var argumentType = functionType instanceof ParameterizedType

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

@@ -59,7 +59,7 @@ class FunctionCallbackWithPlainFunctionBeanIT {
 		.withUserConfiguration(Config.class);
 
 	@Test
-	void functionCallTest2() {
+	void functionCallWithDirectBiFunction() {
 		contextRunner.withPropertyValues("spring.ai.openai.chat.options.model=" + ChatModel.GPT_4_O_MINI.getName())
 			.run(context -> {
 
@@ -72,7 +72,7 @@ void functionCallTest2() {
 					.toolContext(Map.of("sessionId", "123"))
 					.call()
 					.content();
-				System.out.println(content);
+				logger.info(content);
 
 				// Test weatherFunction
 				UserMessage userMessage = new UserMessage(
@@ -91,6 +91,39 @@ void functionCallTest2() {
 			});
 	}
 
+	@Test
+	void functionCallWithBiFunctionClass() {
+		contextRunner.withPropertyValues("spring.ai.openai.chat.options.model=" + ChatModel.GPT_4_O_MINI.getName())
+			.run(context -> {
+
+				OpenAiChatModel chatModel = context.getBean(OpenAiChatModel.class);
+
+				ChatClient chatClient = ChatClient.builder(chatModel).build();
+
+				String content = chatClient.prompt("What's the weather like in San Francisco, Tokyo, and Paris?")
+					.functions("weatherFunctionWithClassBiFunction")
+					.toolContext(Map.of("sessionId", "123"))
+					.call()
+					.content();
+				logger.info(content);
+
+				// Test weatherFunction
+				UserMessage userMessage = new UserMessage(
+						"What's the weather like in San Francisco, Tokyo, and Paris? You can call the following functions 'weatherFunction'");
+
+				ChatResponse response = chatModel.call(new Prompt(List.of(userMessage),
+						OpenAiChatOptions.builder()
+							.withFunction("weatherFunctionWithClassBiFunction")
+							.withToolContext(Map.of("sessionId", "123"))
+							.build()));
+
+				logger.info("Response: {}", response);
+
+				assertThat(response.getResult().getOutput().getContent()).contains("30", "10", "15");
+
+			});
+	}
+
 	@Test
 	void functionCallTest() {
 		contextRunner.withPropertyValues("spring.ai.openai.chat.options.model=" + ChatModel.GPT_4_O_MINI.getName())
@@ -196,6 +229,12 @@ void streamFunctionCallTest() {
 	@Configuration
 	static class Config {
 
+		@Bean
+		@Description("Get the weather in location")
+		public MyBiFunction weatherFunctionWithClassBiFunction() {
+			return new MyBiFunction();
+		}
+
 		@Bean
 		@Description("Get the weather in location")
 		public BiFunction<MockWeatherService.Request, ToolContext, MockWeatherService.Response> weatherFunctionWithContext() {
@@ -220,4 +259,14 @@ public Function<MockWeatherService.Request, MockWeatherService.Response> weather
 
 	}
 
+	public static class MyBiFunction
+			implements BiFunction<MockWeatherService.Request, ToolContext, MockWeatherService.Response> {
+
+		@Override
+		public MockWeatherService.Response apply(MockWeatherService.Request request, ToolContext context) {
+			return new MockWeatherService().apply(request);
+		}
+
+	}
+
 }