Spring Boot Java Coding Rules and Best Practices

A comprehensive checklist and guide for writing clean, maintainable, and scalable Spring Boot applications.

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🚀 1. Project Structure and Organization

• Use the standard package structure: com.yourcompany.projectname
• Organize by layer: controller, service, repository, model, config, dto, exception, util
• For large apps, consider package-by-feature (e.g., user, order, payment)
• Class Naming: PascalCase
• Variable/Method Naming: camelCase
• Avoid abbreviations and acronyms

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🔧 2. Spring Boot Configuration

• Use @ConfigurationProperties over @Value for structured config
• Externalize all configuration in application.yml or application.properties
• Use Spring Profiles (dev, test, prod)
• Validate config with @Validated
• Fail fast on startup misconfigurations

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🧠 3. Dependency Injection and Bean Management

• Prefer constructor injection
• Avoid field injection (@Autowired on fields)
• Be explicit with component scanning (define basePackages)
• Use @Qualifier when multiple beans of the same type exist

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🧾 4. DTOs and Entities

• Never expose entity objects in API responses
• Use DTOs for both request and response payloads
• Use ModelMapper or MapStruct to handle mapping
• Validate incoming DTOs using javax.validation annotations and @Valid

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🧰 5. Service and Repository Layer

• Keep services stateless
• Push reusable logic to utility/helper classes
• Use interface + implementation pattern for services and repositories
• Define transaction boundaries with @Transactional at the service layer

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📡 6. Controller Layer

• Use @RestController for REST APIs
• Handle exceptions globally with @ControllerAdvice
• Always return DTOs or wrapper responses
• Use ResponseEntity for custom status codes and headers

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🧪 7. Testing

• Unit test services and utilities with JUnit + Mockito
• Use @SpringBootTest for integration tests
• Test repositories using @DataJpaTest
• Use MockMvc or WebTestClient to test REST endpoints
• Isolate DB with Testcontainers if possible

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🛡️ 8. Security and Validation

• Enable and configure Spring Security
• Use input validation to prevent injection and data corruption
• Hash passwords using BCryptPasswordEncoder
• Protect endpoints with proper authentication and authorization
• Enable CSRF and configure CORS as required

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🧹 9. Code Quality and Maintainability

• Follow Java code conventions: indentation, braces, spacing, naming
• Use a linter and formatter (e.g., Checkstyle, Spotless)
• Use Lombok with care:
  • Avoid @Data on JPA entities
  • Prefer @Getter, @Setter, @Builder as needed
• Log using SLF4J: LoggerFactory.getLogger(...)
• Avoid using System.out.println
• Create and use custom exceptions

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⚡ 10. Performance and Optimization

• Avoid N+1 query problems using join fetch, @EntityGraph
• Use caching with @Cacheable, Redis, or Caffeine
• Perform long-running tasks with @Async or Spring Batch
• Configure connection pooling (HikariCP is default)
• Profile and monitor the application with Actuator

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🧭 Checklist Summary

• [ ] Use constructor injection
• [ ] Separate DTOs from entities
• [ ] Validate all incoming request data
• [ ] Write unit & integration tests
• [ ] Configure Spring Security properly
• [ ] Externalize all environment-specific config
• [ ] Avoid field injection and circular dependencies
• [ ] Use proper exception handling
• [ ] Monitor and profile using Actuator
• [ ] Document REST APIs with Swagger/OpenAPI

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