ChatClient register functions with explicit input type

 The Lambda functions do not retain the type information, so we need to provide the input type explicitly.

 Resolves #1052

 Co-authored-by: liuzhifei <[email protected]>

Author: tzolov

models/spring-ai-openai/src/test/java/org/springframework/ai/openai/chat/client/OpenAiChatClientMultipleFunctionCallsIT.java

@@ -17,14 +17,17 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 
+import java.lang.reflect.Method;
 import java.util.List;
+import java.util.function.Function;
 import java.util.stream.Collectors;
 
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.condition.EnabledIfEnvironmentVariable;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.ai.chat.client.ChatClient;
+import org.springframework.ai.chat.client.DefaultChatClient;
 import org.springframework.ai.openai.OpenAiTestConfiguration;
 import org.springframework.ai.openai.api.tool.MockWeatherService;
 import org.springframework.ai.openai.testutils.AbstractIT;
@@ -123,4 +126,47 @@ void streamFunctionCallTest() {
 
 	}
 
+	@Test
+	void functionCallWithExplicitInputType() throws NoSuchMethodException {
+
+		var chatClient = ChatClient.create(chatModel);
+
+		Method currentTemp = MyFunction.class.getMethod("getCurrentTemp", MyFunction.Req.class);
+
+		// NOTE: Lambda functions do not retain the type information, so we need to
+		// provide the input type explicitly.
+		MyFunction myFunction = new MyFunction();
+		Function<MyFunction.Req, Object> function = createFunction(myFunction, currentTemp);
+
+		ChatClient.ChatClientRequestSpec chatClientRequestSpec = chatClient.prompt()
+			.user("What's the weather like in Shanghai?")
+			.function("currentTemp", "get current temp", MyFunction.Req.class, function);
+
+		String content = chatClientRequestSpec.call().content();
+
+		assertThat(content).contains("23");
+	}
+
+	public static <T, R> Function<T, R> createFunction(Object obj, Method method) {
+		return (T t) -> {
+			try {
+				return (R) method.invoke(obj, t);
+			}
+			catch (Exception e) {
+				throw new RuntimeException(e);
+			}
+		};
+	}
+
+	public static class MyFunction {
+
+		public record Req(String city) {
+		}
+
+		public String getCurrentTemp(Req req) {
+			return "23";
+		}
+
+	}
+
 }

spring-ai-core/src/main/java/org/springframework/ai/chat/client/ChatClient.java

@@ -189,6 +189,9 @@ interface ChatClientRequestSpec {
 		<I, O> ChatClientRequestSpec function(String name, String description,
 				java.util.function.Function<I, O> function);
 
+		<I, O> ChatClientRequestSpec function(String name, String description, Class<I> inputType,
+				java.util.function.Function<I, O> function);
+
 		ChatClientRequestSpec functions(String... functionBeanNames);
 
 		ChatClientRequestSpec system(String text);

spring-ai-core/src/main/java/org/springframework/ai/chat/client/DefaultChatClient.java

@@ -610,6 +610,11 @@ public <T extends ChatOptions> ChatClientRequestSpec options(T options) {
 
 		public <I, O> ChatClientRequestSpec function(String name, String description,
 				java.util.function.Function<I, O> function) {
+			return this.function(name, description, null, function);
+		}
+
+		public <I, O> ChatClientRequestSpec function(String name, String description, Class<I> inputType,
+				java.util.function.Function<I, O> function) {
 
 			Assert.hasText(name, "the name must be non-null and non-empty");
 			Assert.hasText(description, "the description must be non-null and non-empty");
@@ -618,6 +623,7 @@ public <I, O> ChatClientRequestSpec function(String name, String description,
 			var fcw = FunctionCallbackWrapper.builder(function)
 				.withDescription(description)
 				.withName(name)
+				.withInputType(inputType)
 				.withResponseConverter(Object::toString)
 				.build();
 			this.functionCallbacks.add(fcw);