Spring Boot Project Setup and Configuration¶

Spring Boot project initialization, application properties, build tools (Maven/Gradle), project structure, and clean architecture layering.

Key Facts¶

• Spring Initializr (start.spring.io) generates project skeleton with selected dependencies
• @SpringBootApplication combines @Configuration, @EnableAutoConfiguration, @ComponentScan
• application.properties or application.yml for externalized configuration
• Maven (pom.xml) or Gradle Kotlin (build.gradle.kts) for dependency management
• HikariCP is Spring Boot's default connection pool
• spring.jpa.hibernate.ddl-auto: none/validate for production, update/create for dev

Patterns¶

Clean Architecture Layers¶

domain/          Business logic, models, repository interfaces
  ├── model/     Plain domain objects (no framework annotations)
  ├── repo/      Repository interfaces (WHAT, not HOW)
  └── service/   Business rules (interactors)
data/            Database implementations
  ├── entity/    JPA/JDBC entities with persistence annotations
  ├── repo/      Repository implementations (adapters)
  └── mapper/    Entity <-> Domain model mapping
presentation/    Controllers, DTOs, view templates
  ├── controller/
  ├── dto/       Request/response objects with validation
  └── config/    Spring configurations

Application Properties¶

# Server
server.port=8080

# DataSource
spring.datasource.url=jdbc:postgresql://localhost:5432/mydb
spring.datasource.username=postgres
spring.datasource.password=postgres
spring.datasource.driver-class-name=org.postgresql.Driver

# HikariCP connection pool
spring.datasource.hikari.maximum-pool-size=10
spring.datasource.hikari.connection-timeout=30000

# JPA
spring.jpa.hibernate.ddl-auto=validate
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.format_sql=true
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.PostgreSQLDialect

Adapter Pattern - Decoupling Domain from Data¶

// Domain interface
public interface UserRepo {
    User saveUser(User user);
    User getUserByEmail(String email);
}

// Data layer adapter
@Repository
public class UserRepoAdapter implements UserRepo {
    private final UserCrudRepository crudRepo;
    private final ModelMapper mapper;

    @Override
    public User saveUser(User user) {
        UserEntity entity = mapper.map(user, UserEntity.class);
        UserEntity saved = crudRepo.save(entity);
        return mapper.map(saved, User.class);
    }
}

Domain Models (No Framework Deps)¶

// Java with Lombok
@Data
public class User {
    private Long id;
    private String name;
    private String email;
    private String password;
}

// Kotlin
data class User(
    val id: Long? = null,
    val name: String,
    val email: String,
    val password: String
)

ModelMapper for Entity-Domain Conversion¶

@Configuration
public class MapperConfig {
    @Bean
    public ModelMapper modelMapper() {
        ModelMapper mapper = new ModelMapper();
        mapper.getConfiguration().setMatchingStrategy(MatchingStrategies.STRICT);
        return mapper;
    }
}

Gotchas¶

• Don't write code you won't use - add repository methods only when needed
• Domain models should have no Spring/JPA annotations - that belongs on entities
• Use Long (wrapper) not long (primitive) for IDs - generics require wrapper types
• For prices use Integer for simple cases, BigDecimal for production (fractional currency)
• ddl-auto=update never drops columns/tables - safe for dev but use migrations for production

See Also¶

• [[spring-ioc-beans]] - IoC container and bean management
• [[spring-data-jpa-hibernate]] - JPA entity configuration
• [[spring-data-access-evolution]] - JDBC to JPA progression
• [[database-migrations]] - Flyway and Liquibase