Java + GenAI: The Complete Guide to Spring AI for Java Developers.

@RestController
@RequestMapping("/api/ai")
public class AiStreamingController {

    private final ChatClient chatClient;

    public AiStreamingController(ChatClient.Builder chatClientBuilder) {
        this.chatClient = chatClientBuilder.build();
    }

    // Stream tokens in real-time as Server-Sent Events (SSE)
    @GetMapping(value = "/stream", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
    public Flux<String> streamAiResponse(@RequestParam String prompt) {
        return chatClient.prompt()
                .user(prompt)
                .stream()
                .content();
    }
}

@Service
public class DocumentRagService {

    private final ChatClient chatClient;
    private final VectorStore vectorStore;

    public DocumentRagService(ChatClient.Builder builder, VectorStore vectorStore) {
        this.chatClient = builder.build();
        this.vectorStore = vectorStore;
    }

    public String askCompanyPolicy(String userQuestion) {
        // Step 1: Search top 3 similar documents from PGVector with metadata filter
        List<Document> similarDocuments = vectorStore.similaritySearch(
            SearchRequest.query(userQuestion)
                .withTopK(3)
                .withSimilarityThreshold(0.75)
        );

        String context = similarDocuments.stream()
            .map(Document::getContent)
            .collect(Collectors.joining("\n---\n"));

        // Step 2: Pass retrieved context to LLM
        return chatClient.prompt()
            .system("You are an HR assistant. Answer strictly using only the provided context.")
            .user(u -> u.text("Context:\n{context}\n\nQuestion: {question}")
                        .param("context", context)
                        .param("question", userQuestion))
            .call()
            .content();
    }
}

@Configuration
public class ToolConfiguration {

    public record WeatherRequest(String city) {}
    public record WeatherResponse(String city, double tempC, String condition) {}

    // Expose a standard Java java.util.Function as an AI Tool
    @Bean
    @Description("Get current live weather temperature and condition for a given city")
    public Function<WeatherRequest, WeatherResponse> currentWeatherFunction() {
        return request -> {
            // Live API or Database call
            return new WeatherResponse(request.city(), 28.5, "Partly Cloudy");
        };
    }
}

// In your service:
public String askWithTools(String question) {
    return chatClient.prompt()
        .user(question)
        .functions("currentWeatherFunction") // Activated!
        .call()
        .content();
}

@Service
public class CustomerSupportBot {

    private final ChatClient chatClient;

    public CustomerSupportBot(ChatClient.Builder builder, VectorStore vectorStore) {
        this.chatClient = builder
            // Advisor 1: Keep last 10 messages of conversation in memory per session
            .defaultAdvisors(
                new MessageChatMemoryAdvisor(new InMemoryChatMemory()),
                // Advisor 2: Automatically attach relevant RAG vectors
                new QuestionAnswerAdvisor(vectorStore, SearchRequest.defaults())
            )
            .build();
    }

    public String chatWithUser(String conversationId, String message) {
        return chatClient.prompt()
            .advisors(a -> a.param(AbstractChatMemoryAdvisor.CHAT_MEMORY_CONVERSATION_ID_KEY, conversationId))
            .user(message)
            .call()
            .content();
    }
}