# Java & Maven
sudo apt install openjdk-17-jdk maven
# PostgreSQL (Docker)
docker run -d -p 5432:5432 --name postgres </span>
-e POSTGRES_USER=gateway </span>
-e POSTGRES_PASSWORD=secret </span>
-e POSTGRES_DB=gateway_cache </span>
postgres:15

git clone https://github.com/yourrepo/product-catalog-java.git
cd product-catalog-java

src/
├── main/
│   ├── java/
│   │   ├── com.productcatalog/
│   │   │   ├── CandyModule/       # SKU/Inventory (now JPA entities)
│   │   │   ├── FashionModule/     # Size/Color (now JPA entities)
│   │   │   ├── VirtualTryOn/      # Avatar/AR
│   │   │   └── ProductCatalogApplication.java
│   └── resources/
│       ├── application.yml        # PostgreSQL config
│       ├── db/
│       │   └── migration/        # Flyway scripts
│       └── logback.xml
└── test/                         # JUnit tests

<dependencies>
<!-- Spring Boot -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<!-- PostgreSQL Driver -->
<dependency>
<groupId>org.postgresql</groupId>
<artifactId>postgresql</artifactId>
<scope>runtime</scope>
</dependency>
<!-- Flyway for migrations -->
<dependency>
<groupId>org.flywaydb</groupId>
<artifactId>flyway-core</artifactId>
</dependency>
<!-- Testing -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.testcontainers</groupId>
<artifactId>postgresql</artifactId>
<scope>test</scope>
</dependency>
</dependencies>

// CandyModule/SKU.java
@Entity
@Table(name = "skus")
public class SKU {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column(name = "code", unique = true, length = 8)
private String code;  // Format: "ABC-1234"
@Column(name = "inventory")
private int inventory;
}

public interface SKURepository extends JpaRepository<SKU, Long> {
@Query("SELECT s FROM SKU s WHERE s.code = :code")
Optional<SKU> findByCode(@Param("code") String code);
}

@Service
@Transactional
public class SKUService {
@Autowired
private SKURepository skuRepo;
public void createSKU(SKU sku) {
// Database will validate format via CHECK constraint
skuRepo.save(sku);
}
}

@RestController
@RequestMapping("/api/candy")
public class CandyController {
@Autowired
private SKUService skuService;
@PostMapping("/skus")
public ResponseEntity<String> addSKU(@RequestBody SKU sku) {
skuService.createSKU(sku);
return ResponseEntity.ok("SKU created");
}
}

public class InvalidSKUException extends RuntimeException {
public InvalidSKUException(String message) {
super(message);
}
}

@ControllerAdvice
public class GlobalExceptionHandler {
@ExceptionHandler(DataIntegrityViolationException.class)
public ResponseEntity<String> handleDataError(DataIntegrityViolationException ex) {
return ResponseEntity.badRequest().body("Database constraint violation");
}
@ExceptionHandler(InvalidSKUException.class)
public ResponseEntity<String> handleSKUError(InvalidSKUException ex) {
return ResponseEntity.badRequest().body(ex.getMessage());
}
}

@Test
void testInvalidSKU() {
SKUService service = new SKUService();
SKU invalidSKU = new SKU();
invalidSKU.setCode("INVALID");
assertThrows(ConstraintViolationException.class, () -> service.createSKU(invalidSKU));
}

@SpringBootTest
@Testcontainers
public class CandyControllerIT {
@Container
static PostgreSQLContainer<?> postgres = new PostgreSQLContainer<>("postgres:15");
@DynamicPropertySource
static void configureProperties(DynamicPropertyRegistry registry) {
registry.add("spring.datasource.url", postgres::getJdbcUrl);
registry.add("spring.datasource.username", postgres::getUsername);
registry.add("spring.datasource.password", postgres::getPassword);
}
@Test
void createSKU_ValidFormat_Returns200() {
// Test with actual PostgreSQL instance
}
}

mvn spring-boot:run
# Access: http://localhost:8080/api/candy/skus

FROM eclipse-temurin:17-jdk
COPY target/product-catalog-0.0.1.jar app.jar
ENTRYPOINT ["java","-jar","app.jar"]

mvn package
docker build -t product-catalog .
docker run -p 8080:8080 --network host product-catalog

spring:
datasource:
url: jdbc:postgresql://localhost:5432/gateway_cache
username: gateway
password: secret
hikari:
maximum-pool-size: 10
jpa:
hibernate:
ddl-auto: validate
show-sql: true
properties:
hibernate:
dialect: org.hibernate.dialect.PostgreSQLDialect
flyway:
locations: classpath:db/migration

-- In V1__Initial_schema.sql
ALTER TABLE skus ADD CONSTRAINT valid_sku_format
CHECK (code ~ '^[A-Z]{3}-\d{4}$');

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>

http://localhost:8080/actuator/health
http://localhost:8080/actuator/metrics
http://localhost:8080/actuator/flyway