Introduction: From ConnectionError to Production-Ready in 15 Minutes

I encountered a critical ConnectionError: timeout issue at 3 AM last week when our production AI feature stopped responding. The culprit? Hardcoded API endpoints and missing retry logic. After fixing this, I realized most developers face similar challenges when integrating AI APIs into Spring Boot applications. This guide provides a battle-tested, production-ready implementation that eliminates these common pitfalls.

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Project Setup and Dependencies

Create a new Spring Boot project or add these dependencies to your existing pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
         http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.2.0</version>
        <relativePath/>
    </parent>
    
    <groupId>com.example</groupId>
    <artifactId>spring-boot-ai-integration</artifactId>
    <version>1.0.0</version>
    <packaging>jar</packaging>
    
    <properties>
        <java.version>17</java.version>
        <spring-cloud.version>2023.0.0</spring-cloud.version>
    </properties>
    
    <dependencies>
        <!-- Spring Boot Web -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        
        <!-- Spring Boot Validation -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-validation</artifactId>
        </dependency>
        
        <!-- HTTP Client (Spring WebClient) -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
        </dependency>
        
        <!-- Resilience4j for retry and circuit breaker -->
        <dependency>
            <groupId>io.github.resilience4j</groupId>
            <artifactId>resilience4j-spring-boot3</artifactId>
            <version>2.2.0</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>
        
        <!-- Jackson for JSON processing -->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
        </dependency>
        
        <!-- Lombok -->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        
        <!-- Configuration Processor -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
        
        <!-- Test Dependencies -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
    
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

Configuration Properties

Create your application.yml with HolySheep AI configuration:

spring:
  application:
    name: spring-boot-ai-integration
  jackson:
    serialization:
      write-dates-as-timestamps: false
    default-property-inclusion: non_null

server:
  port: 8080


HolySheep AI Configuration

ai:
  holysheep:
    base-url: https://api.holysheep.ai/v1
    api-key: YOUR_HOLYSHEEP_API_KEY
    timeout-seconds: 30
    max-retries: 3
    retry-delay-ms: 1000
    connection-pool-size: 100
    max-codec-resource-pool-size: 200


Resilience4j Configuration

resilience4j:
  retry:
    instances:
      aiApiRetry:
        max-attempts: 3
        wait-duration: 1s
        retry-exceptions:
          - java.io.IOException
          - java.util.concurrent.TimeoutException
          - org.springframework.web.reactive.function.client.WebClientResponseException$ServiceUnavailable
        ignore-exceptions:
          - org.springframework.web.reactive.function.client.WebClientResponseException$BadRequest
          - org.springframework.web.reactive.function.client.WebClientResponseException$Unauthorized
  circuitbreaker:
    instances:
      aiApiCircuitBreaker:
        sliding-window-size: 10
        failure-rate-threshold: 50
        wait-duration-in-open-state: 30s
        permitted-number-of-calls-in-half-open-state: 5
        sliding-window-type: COUNT_BASED

logging:
  level:
    com.example.ai: DEBUG
    org.springframework.web.reactive: DEBUG

Core Implementation: AI Service Layer

Here's the complete production-ready AI service with WebClient, retry logic, and circuit breaker:

package com.example.ai.service;

import com.example.ai.config.HolySheepProperties;
import com.example.ai.dto.*;
import com.fasterxml.jackson.databind.ObjectMapper;
import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Service;
import org.springframework.web.reactive.function.client.WebClient;
import org.springframework.web.reactive.function.client.WebClientResponseException;
import reactor.core.publisher.Mono;
import reactor.util.retry.Retry;

import jakarta.annotation.PostConstruct;
import java.time.Duration;
import java.util.List;
import java.util.Map;

@Slf4j
@Service
@RequiredArgsConstructor
public class HolySheepAIService {
    
    private final HolySheepProperties properties;
    private final ObjectMapper objectMapper;
    private WebClient webClient;
    
    @PostConstruct
    public void init() {
        this.webClient = WebClient.builder()
                .baseUrl(properties.getBaseUrl())
                .defaultHeader("Authorization", "Bearer " + properties.getApiKey())
                .defaultHeader("Content-Type", "application/json")
                .codecs(configurer -> configurer
                        .defaultCodecs()
                        .maxInMemorySize(16 * 1024 * 1024)) // 16MB
                .build();
    }
    
    /**
     * Send a chat completion request to HolySheep AI
     * Supports multiple models: gpt-4.1, claude-sonnet-4.5, gemini-2.5-flash, deepseek-v3.2
     * 
     * 2026 Pricing (per 1M tokens):
     * - GPT-4.1: $8.00
     * - Claude Sonnet 4.5: $15.00
     * - Gemini 2.5 Flash: $2.50
     * - DeepSeek V3.2: $0.42
     */
    public Mono createChatCompletion(ChatCompletionRequest request) {
        log.info("Sending chat completion request with model: {}", request.getModel());
        
        return webClient.post()
                .uri("/chat/completions")
                .bodyValue(request)
                .retrieve()
                .bodyToMono(ChatCompletionResponse.class)
                .timeout(Duration.ofSeconds(properties.getTimeoutSeconds()))
                .doOnSuccess(response -> log.info("Chat completion successful. Usage: {}", response.getUsage()))
                .doOnError(error -> log.error("Chat completion failed: {}", error.getMessage()))
                .retryWhen(Retry.backoff(properties.getMaxRetries(), 
                        Duration.ofMillis(properties.getRetryDelayMs()))
                        .filter(this::isRetryable)
                        .onRetryExceeded(error -> log.error("Retry limit exceeded")))
                .onErrorResume(this::handleError);
    }
    
    /**
     * Stream chat completions for real-time responses
     */
    public Mono createStreamingChatCompletion(ChatCompletionRequest request) {
        log.info("Starting streaming chat completion with model: {}", request.getModel());
        
        return webClient.post()
                .uri("/chat/completions")
                .bodyValue(request)
                .retrieve()
                .bodyToMono(String.class)
                .timeout(Duration.ofSeconds(properties.getTimeoutSeconds() * 2))
                .doOnNext(chunk -> log.debug("Received streaming chunk: {}", chunk));
    }
    
    /**
     * Check account balance
     */
    public Mono getBalance() {
        log.info("Fetching account balance from HolySheep AI");
        
        return webClient.get()
                .uri("/balance")
                .retrieve()
                .bodyToMono(BalanceResponse.class)
                .doOnSuccess(response -> log.info("Balance retrieved: {}", response));
    }
    
    private boolean isRetryable(Throwable throwable) {
        if (throwable instanceof WebClientResponseException e) {
            return e.getStatusCode().is5xxServerError() ||
                   e.getStatusCode().value() == 429; // Rate limit
        }
        return throwable instanceof java.io.IOException ||
               throwable instanceof java.util.concurrent.TimeoutException;
    }
    
    private Mono handleError(Throwable error) {
        if (error instanceof WebClientResponseException e) {
            log.error("API Error - Status: {}, Body: {}", 
                    e.getStatusCode(), e.getResponseBodyAsString());
            
            return Mono.error(new AIApiException(
                    "AI API Error: " + e.getStatusCode() + " - " + e.getMessage(),
                    e.getStatusCode().value(),
                    e.getResponseBodyAsString()
            ));
        }
        
        log.error("Unexpected error during AI API call: {}", error.getMessage());
        return Mono.error(new AIApiException("AI API call failed: " + error.getMessage(), 0, null));
    }
}

/**
 * Custom exception for AI API errors
 */
class AIApiException extends RuntimeException {
    private final int statusCode;
    private final String responseBody;
    
    public AIApiException(String message, int statusCode, String responseBody) {
        super(message);
        this.statusCode = statusCode;
        this.responseBody = responseBody;
    }
    
    public int getStatusCode() { return statusCode; }
    public String getResponseBody() { return responseBody; }
}

DTO Classes and Request/Response Models

package com.example.ai.dto;

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.util.List;
import java.util.Map;

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
@JsonInclude(JsonInclude.Include.NON_NULL)
public class ChatCompletionRequest {
    
    private String model; // "gpt-4.1", "claude-sonnet-4.5", "gemini-2.5-flash", "deepseek-v3.2"
    private List messages;
    private Double temperature;
    private Integer maxTokens;
    private Double topP;
    private Integer n;
    private Boolean stream;
    private String stop;
    
    @JsonProperty("presence_penalty")
    private Double presencePenalty;
    
    @JsonProperty("frequency_penalty")
    private Double frequencyPenalty;
    
    @JsonProperty("user")
    private String user;
    
    private Map<String, Object> functions;
    private String functionCall;
}

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
@JsonInclude(JsonInclude.Include.NON_NULL)
public class Message {
    private String role; // "system", "user", "assistant", "function"
    private String content;
    private String name;
    private String functionCall;
    private FunctionCall functionCallDetails;
}

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
class FunctionCall {
    private String name;
    private String arguments; // JSON string
}

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
@JsonInclude(JsonInclude.Include.NON_NULL)
public class ChatCompletionResponse {
    private String id;
    private String object;
    private long created;
    private String model;
    private List<Choice> choices;
    private Usage usage;
    private String serviceTier;
    private String systemFingerprint;
}

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
class Choice {
    private int index;
    private Message message;
    private Object logprobs;
    private String finishReason;
}

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
class Usage {
    @JsonProperty("prompt_tokens")
    private int promptTokens;
    
    @JsonProperty("completion_tokens")
    private int completionTokens;
    
    @JsonProperty("total_tokens")
    private int totalTokens;
}

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
class BalanceResponse {
    private String hsaBalance;
    private String totalBalance;
    private String currency;
}

REST Controller with Production Features

package com.example.ai.controller;

import com.example.ai.dto.*;
import com.example.ai.service.HolySheepAIService;
import io.github.resilience4j.circuitbreaker.annotation.CircuitBreaker;
import io.github.resilience4j.retry.annotation.Retry;
import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import reactor.core.publisher.Mono;
import reactor.core.scheduler.Schedulers;

import jakarta.validation.Valid;
import java.util.List;
import java.util.Map;

@Slf4j
@RestController
@RequestMapping("/api/v1/ai")
@RequiredArgsConstructor
public class AIController {
    
    private final HolySheepAIService aiService;
    
    /**
     * Chat completion endpoint with circuit breaker and retry
     */
    @PostMapping("/chat")
    @CircuitBreaker(name = "aiApiCircuitBreaker", fallbackMethod = "chatFallback")
    @Retry(name = "aiApiRetry")
    public Mono<ResponseEntity<ChatCompletionResponse>> createChat(
            @Valid @RequestBody ChatRequest request) {
        
        log.info("Received chat request with model: {}", request.getModel());
        
        ChatCompletionRequest completionRequest = ChatCompletionRequest.builder()
                .model(request.getModel())
                .messages(request.getMessages())
                .temperature(request.getTemperature() != null ? request.getTemperature() : 0.7)
                .maxTokens(request.getMaxTokens() != null ? request.getMaxTokens() : 2048)
                .stream(false)
                .build();
        
        return aiService.createChatCompletion(completionRequest)
                .map(ResponseEntity::ok)
                .onErrorResume(error -> Mono.just(
                        ResponseEntity.internalServerError().body(null)));
    }
    
    /**
     * Streaming chat completion endpoint
     */
    @PostMapping(value = "/chat/stream", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
    public Mono<ResponseEntity<String>> createStreamingChat(
            @Valid @RequestBody ChatRequest request) {
        
        log.info("Received streaming chat request");
        
        ChatCompletionRequest completionRequest = ChatCompletionRequest.builder()
                .model(request.getModel())
                .messages(request.getMessages())
                .temperature(request.getTemperature() != null ? request.getTemperature() : 0.7)
                .maxTokens(request.getMaxTokens() != null ? request.getMaxTokens() : 2048)
                .stream(true)
                .build();
        
        return aiService.createStreamingChatCompletion(completionRequest)
                .map(ResponseEntity::ok)
                .onErrorResume(error -> Mono.just(
                        ResponseEntity.internalServerError()
                                .body("data: {\"error\": \"" + error.getMessage() + "\"}\n\n")));
    }
    
    /**
     * Get account balance
     */
    @GetMapping("/balance")
    public Mono<ResponseEntity<BalanceResponse>> getBalance() {
        log.info("Balance check requested");
        return aiService.getBalance()
                .map(ResponseEntity::ok)
                .onErrorResume(error -> Mono.just(
                        ResponseEntity.internalServerError().body(null)));
    }
    
    /**
     * Health check endpoint
     */
    @GetMapping("/health")
    public Mono<ResponseEntity<Map<String, Object>>> healthCheck() {
        return aiService.getBalance()
                .map(balance -> ResponseEntity.ok(Map.of(
                        "status", "UP",
                        "provider", "HolySheep AI",
                        "balance", balance.getTotalBalance(),
                        "latency_ms", System.currentTimeMillis()
                )))
                .onErrorResume(error -> Mono.just(
                        ResponseEntity.ok(Map.of(
                                "status", "DOWN",
                                "error", error.getMessage()
                        ))));
    }
    
    /**
     * Fallback method for circuit breaker
     */
    public Mono<ResponseEntity<ChatCompletionResponse>> chatFallback(
            ChatRequest request, Throwable error) {
        
        log.error("Circuit breaker triggered for chat request. Error: {}", error.getMessage());
        
        return Mono.fromSupplier(() -> ResponseEntity.ok(
                ChatCompletionResponse.builder()
                        .choices(List.of(
                                ChatCompletionResponse.Choice.builder()
                                        .index(0)
                                        .message(Message.builder()
                                                .role("assistant")
                                                .content("I apologize, but I'm experiencing high demand right now. " +
                                                        "Please try again in a few moments. " +
                                                        "HolySheep AI offers 85%+ savings compared to standard APIs " +
                                                        "with sub-50ms latency.")
                                                .build())
                                        .finishReason("error")
                                        .build()
                        ))
                        .build()
        ));
    }
}

@Data
class ChatRequest {
    private String model = "deepseek-v3.2"; // Default to most cost-effective model
    @Valid
    private List<Message> messages;
    private Double temperature;
    private Integer maxTokens;
}

Configuration Properties Class

package com.example.ai.config;

import lombok.Data;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

@Data
@Component
@ConfigurationProperties(prefix = "ai.holysheep")
public class HolySheepProperties {
    
    private String baseUrl = "https://api.holysheep.ai/v1";
    private String apiKey;
    private int timeoutSeconds = 30;
    private int maxRetries = 3;
    private long retryDelayMs = 1000;
    private int connectionPoolSize = 100;
    private int maxCodecResourcePoolSize = 200;
}

Testing the Integration

package com.example.ai.service;

import com.example.ai.dto.*;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.ActiveProfiles;
import reactor.core.publisher.Mono;
import reactor.test.StepVerifier;

import java.util.List;

import static org.junit.jupiter.api.Assertions.*;

@SpringBootTest
@ActiveProfiles("test")
class HolySheepAIServiceIntegrationTest {
    
    @Autowired
    private HolySheepAIService aiService;
    
    @Autowired
    private HolySheepProperties properties;
    
    @Test
    void testSimpleChatCompletion()

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