# 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

psql -h localhost -p 5432 -U gateway -d gateway_cache
# Password: secret

src/
├── main/
│   ├── java/
│   │   ├── com.productcatalog/
│   │   │   ├── model/            # JPA Entities
│   │   │   ├── repository/       # PostgreSQL Repositories
│   │   │   ├── service/          # Business Logic
│   │   │   └── ProductCatalogApplication.java
│   └── resources/
│       ├── application.yml       # PostgreSQL Config
│       ├── db/
│       │   └── migration/       # Flyway scripts (optional)
│       └── logback.xml
└── test/                        # JUnit tests

<dependencies>
<!-- Spring Data JPA for PostgreSQL -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.postgresql</groupId>
<artifactId>postgresql</artifactId>
<scope>runtime</scope>
</dependency>
<!-- Flyway for migrations (optional) -->
<dependency>
<groupId>org.flywaydb</groupId>
<artifactId>flyway-core</artifactId>
</dependency>
</dependencies>

spring:
datasource:
url: jdbc:postgresql://localhost:5432/gateway_cache
username: gateway
password: secret
hikari:
maximum-pool-size: 10
jpa:
hibernate:
ddl-auto: validate # Match your schema
show-sql: true
properties:
hibernate:
dialect: org.hibernate.dialect.PostgreSQLDialect

@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) {
// PostgreSQL will enforce the UNIQUE constraint
skuRepo.save(sku);
}
}

spring:
jpa:
hibernate:
ddl-auto: update # For dev only

CREATE TABLE skus (
id BIGSERIAL PRIMARY KEY,
code VARCHAR(8) UNIQUE NOT NULL CHECK (code ~ '^[A-Z]{3}-\d{4}$'),
inventory INTEGER NOT NULL DEFAULT 0
);

@SpringBootTest
@Testcontainers
public class SKUServiceIntegrationTest {
@Container
static PostgreSQLContainer<?> postgres = new PostgreSQLContainer<>("postgres:15")
.withDatabaseName("testdb")
.withUsername("test")
.withPassword("test");
@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 testSkuPersistence() {
SKU sku = new SKU("ABC-1234", 100);
skuRepo.save(sku);
assertNotNull(sku.getId());
}
}

mvn spring-boot:run

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

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

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