Spring Boot - 🧠 Guided Exercise: "Student Management System" (with Spring Boot + H2 + Validation + Error Handling)

[akash-coded]

🧠 Exercise: "Student Management System" (with Spring Boot + H2 + Validation + Error Handling)

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🔧 Objective:

Build a Student Management API using Spring Boot, storing data in an H2 in-memory DB, with layered architecture, validation, and custom error handling.

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📦 Requirements:

1. Spring Boot project (use start.spring.io) with these dependencies:

   • Spring Web
   • Spring Data JPA
   • H2 Database
   • Spring Boot DevTools
   • Lombok
   • Validation (spring-boot-starter-validation)
   • Spring Boot Actuator (for later monitoring)

2. Port: Run on port 8081

3. Database: Use H2 in-memory database. Console enabled at /h2-console

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🗃️ Folder Structure

src/
└── main/
    └── java/
        └── com/example/studentmgmt/
            ├── controller/
            │   └── StudentController.java
            ├── service/
            │   ├── StudentService.java   ← interface
            │   └── impl/StudentServiceImpl.java
            ├── repository/
            │   └── StudentRepository.java
            ├── exception/
            │   ├── StudentNotFoundException.java
            │   └── GlobalExceptionHandler.java
            ├── model/
            │   └── Student.java
            └── StudentMgmtApplication.java

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🧱 Step-by-Step Exercise Guide

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1️⃣ Model Class: Student.java

@Entity
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Student {
    
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @NotBlank(message = "Name is mandatory")
    private String name;

    @Email(message = "Invalid email format")
    private String email;

    @Min(value = 18, message = "Minimum age is 18")
    private int age;
}

✅ Learnings: Request validation annotations like @NotBlank, @Email, @Min

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2️⃣ Repository Interface

@Repository
public interface StudentRepository extends JpaRepository<Student, Long> {
}

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3️⃣ Service Interface: StudentService.java

public interface StudentService {
    Student createStudent(Student student);
    List<Student> getAllStudents();
    Student getStudentById(Long id);
    void deleteStudent(Long id);
}

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4️⃣ Service Implementation: StudentServiceImpl.java

@Service
public class StudentServiceImpl implements StudentService {

    @Autowired
    private StudentRepository studentRepository;

    @Override
    public Student createStudent(Student student) {
        return studentRepository.save(student);
    }

    @Override
    public List<Student> getAllStudents() {
        return studentRepository.findAll();
    }

    @Override
    public Student getStudentById(Long id) {
        return studentRepository.findById(id)
            .orElseThrow(() -> new StudentNotFoundException("Student not found with id: " + id));
    }

    @Override
    public void deleteStudent(Long id) {
        if (!studentRepository.existsById(id)) {
            throw new StudentNotFoundException("Cannot delete. No student found with id: " + id);
        }
        studentRepository.deleteById(id);
    }
}

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5️⃣ Exception Class: StudentNotFoundException.java

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

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6️⃣ Global Exception Handler

@RestControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(StudentNotFoundException.class)
    public ResponseEntity<?> handleStudentNotFound(StudentNotFoundException ex) {
        return new ResponseEntity<>(Map.of("error", ex.getMessage()), HttpStatus.NOT_FOUND);
    }

    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity<?> handleValidationErrors(MethodArgumentNotValidException ex) {
        Map<String, String> errors = new HashMap<>();
        ex.getBindingResult().getFieldErrors().forEach(err -> 
            errors.put(err.getField(), err.getDefaultMessage()));
        return new ResponseEntity<>(errors, HttpStatus.BAD_REQUEST);
    }
}

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7️⃣ Controller: StudentController.java

@RestController
@RequestMapping("/api/students")
public class StudentController {

    @Autowired
    private StudentService studentService;

    @PostMapping
    public ResponseEntity<Student> create(@Valid @RequestBody Student student) {
        return new ResponseEntity<>(studentService.createStudent(student), HttpStatus.CREATED);
    }

    @GetMapping
    public List<Student> getAll() {
        return studentService.getAllStudents();
    }

    @GetMapping("/{id}")
    public Student getById(@PathVariable Long id) {
        return studentService.getStudentById(id);
    }

    @DeleteMapping("/{id}")
    public ResponseEntity<Void> delete(@PathVariable Long id) {
        studentService.deleteStudent(id);
        return ResponseEntity.noContent().build();
    }
}

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8️⃣ application.properties

server.port=8081

# H2 database config
spring.datasource.url=jdbc:h2:mem:studentdb
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
spring.h2.console.enabled=true
spring.h2.console.path=/h2-console

# Hibernate
spring.jpa.hibernate.ddl-auto=update

# Actuator
management.endpoints.web.exposure.include=*
management.endpoint.health.show-details=always

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🧪 Test This With:

Sample JSON for POST /api/students

{
  "name": "Sanya Mehta",
  "email": "sanya.mehta@example.com",
  "age": 22
}

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🚨 Expected Errors to Trigger:

• Try sending age: 16 → should trigger validation
• Try fetching or deleting /api/students/999 → custom not-found error

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🧩 Suggested Add-ons for Mastery

• Add PUT /api/students/{id} to update
• Add optional filter by age or name
• Enable logging using SLF4J
• Unit test the controller & service layers

[prasetha21-max]

PRASETHA N
student-mgmt.zip