Spring Boot Annotations: Powering Mid-Scale Apps

Building a mid-scale Spring Boot app—like an Employee Management System—means organizing code into layers: Configuration, Entity, Controller, Service, and Repository. Annotations are the glue that makes these layers work together. This post shares the essential annotations for a mid-scale project, with clear examples to help you create robust apps. Perfect for developers stepping up to bigger challenges!

1. Configuration Layer

Sets up your app’s foundation.

@SpringBootApplicationKicks off your app with auto-configuration.

@SpringBootApplication

public class EmployeeApp {

public static void main(String[] args) {

SpringApplication.run(EmployeeApp.class, args);

}

}

@ConfigurationDefines custom settings or beans.

@Configuration

public class AppConfig {

@Bean

public PasswordEncoder encoder() {

return new BCryptPasswordEncoder();

}

}

@BeanCreates reusable objects for Spring.Example: See above (PasswordEncoder).

2. Entity Layer

Shapes your data, like employee records.

@EntityMarks a class as a database table.

@Entity

public class Employee {

@Id

@GeneratedValue(strategy = GenerationType.AUTO)

private Long id;

private String name;

private String email;

}

@IdSets the unique ID for each record.Example: See above.

@GeneratedValueAuto-creates IDs.Example: See above.

@ColumnMaps fields to table columns.

@Column(unique = true)

private String email;

@NotNullEnsures fields aren’t empty.

@NotNull

private String name;

3. Controller Layer

Handles API requests for your app.

@RestControllerManages REST API requests, returning data like JSON.

@RestController

@RequestMapping("/api/employees")

public class EmployeeController {

@GetMapping

public List<Employee> getAll() {

return service.findAll();

}

}

@RequestMappingSets a base URL for endpoints.Example: See above.

@GetMapping, @PostMapping, @PutMapping, @DeleteMappingTie methods to HTTP actions.

@PostMapping

public Employee create(@RequestBody Employee employee) {

return service.save(employee);

}

@RequestBodyTurns JSON into Java objects.Example: See above.

@PathVariableGrabs URL values (e.g., /employees/1).

@GetMapping("/{id}")

public Employee getById(@PathVariable Long id) {

return service.findById(id);

}

@ValidChecks input data for errors.

@PostMapping

public Employee create(@Valid @RequestBody Employee employee) {

return service.save(employee);

}

4. Service Layer

Runs your app’s core logic.

@ServiceMarks a class for business logic.

@Service

public class EmployeeService {

public Employee save(Employee employee) {

return repo.save(employee);

}

}

@AutowiredLinks services to other components.

@Autowired

private EmployeeRepository repo;

@TransactionalKeeps database actions safe and complete.

@Transactional

public Employee save(Employee employee) {

return repo.save(employee);

}

5. Repository Layer

Connects to your database.

@RepositoryHandles database tasks.

@Repository

public interface EmployeeRepository extends JpaRepository<Employee, Long> {

}

@QueryCreates custom database queries.

@Query("SELECT e FROM Employee e WHERE e.email = ?1")

Employee findByEmail(String email);

Example: Employee Management App

Here’s a working app using these annotations:

// App setup

@SpringBootApplication

public class EmployeeApp {

public static void main(String[] args) {

SpringApplication.run(EmployeeApp.class, args);

}

}

// Data model

@Entity

public class Employee {

@Id

@GeneratedValue(strategy = GenerationType.AUTO)

private Long id;

@NotNull

@Column

private String name;

@NotNull

@Column(unique = true)

private String email;

// getters and setters

}

// Database access

@Repository

public interface EmployeeRepository extends JpaRepository<Employee, Long> {

@Query("SELECT e FROM Employee e WHERE e.email = ?1")

Employee findByEmail(String email);

}

// Business logic

@Service

public class EmployeeService {

@Autowired

private EmployeeRepository repo;

@Transactional

public Employee save(Employee employee) {

return repo.save(employee);

}

public Employee findById(Long id) {

return repo.findById(id).orElse(null);

}

}

// API endpoints

@RestController

@RequestMapping("/api/employees")

public class EmployeeController {

@Autowired

private EmployeeService service;

@PostMapping

public Employee create(@Valid @RequestBody Employee employee) {

return service.save(employee);

}

@GetMapping("/{id}")

public Employee getById(@PathVariable Long id) {

return service.findById(id);

}

}

Try it out: send a POST to /api/employees or GET /api/employees/1 to manage employees!

Why These Matter

These annotations handle everything a mid-scale app needs:

Setup: Launch and configure your app.

Data: Store and validate employee details.

APIs: Create endpoints for adding or viewing data.

Logic: Process and protect database operations.

Database: Fetch or save data effortlessly.

Quick Tips

Test it: Use Postman to try your APIs.

Avoid pitfalls:

Always add @Id to entities.

Use @Valid with @NotNull for clean data.

Don’t skip @Transactional for saves.

Grow further: Next, try @ExceptionHandler for errors or @ManyToOne for linking data.

These annotations will fuel your mid-scale Spring Boot projects. What app are you building next? 🚀