Spring Boot - Request Handling - 🧪 Exercise: CustomerPlus API – Multiple Request Styles and Structured Response

[akash-coded]

🧪 Exercise: CustomerPlus API – Multiple Request Styles and Structured Response

🎯 Objective

Build a Spring Boot REST API that:

• Accepts customer creation requests via different mechanisms (@RequestBody, @RequestParam, @PathVariable)
• Returns structured and well-documented JSON responses using DTOs
• Demonstrates API evolution with variant endpoints
• Follows clean architecture: controller → service → repository → model + DTO
• Uses Spring’s ResponseEntity, optional chaining, and null-safe responses

---

🛠 Project Setup

📁 Folder Structure

com.example.customerplus
├── controller
│   └── CustomerController.java
├── dto
│   └── CustomerDTO.java
├── model
│   └── Customer.java
├── repository
│   └── CustomerRepository.java
├── service
│   ├── CustomerService.java
│   └── CustomerServiceImpl.java
├── exception
│   └── GlobalExceptionHandler.java
├── util
│   └── ApiResponse.java
└── CustomerPlusApplication.java

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🧾 Step-by-Step Instructions

1️⃣ Add Dependencies in pom.xml

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>com.h2database</groupId>
        <artifactId>h2</artifactId>
        <scope>runtime</scope>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
</dependencies>

---

2️⃣ application.properties

server.port=8082
spring.h2.console.enabled=true
spring.datasource.url=jdbc:h2:mem:testdb
spring.datasource.driverClassName=org.h2.Driver
spring.jpa.hibernate.ddl-auto=update
spring.datasource.username=sa
spring.datasource.password=

---

3️⃣ Model: Customer.java

@Entity
public class Customer {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String email;
    private String city;
    private int age;
}

---

4️⃣ DTO: CustomerDTO.java

public class CustomerDTO {
    private String name;
    private String email;

    public CustomerDTO(Customer customer) {
        this.name = customer.getName();
        this.email = customer.getEmail();
    }
}

---

5️⃣ Repository

@Repository
public interface CustomerRepository extends JpaRepository<Customer, Long> {
    List<Customer> findByCity(String city);
}

---

6️⃣ Service Interface & Impl

public interface CustomerService {
    Customer createCustomer(Customer customer);
    List<Customer> getCustomersByCity(String city);
    Optional<Customer> getCustomerById(Long id);
}

@Service
public class CustomerServiceImpl implements CustomerService {
    @Autowired private CustomerRepository repo;

    public Customer createCustomer(Customer customer) {
        return repo.save(customer);
    }

    public List<Customer> getCustomersByCity(String city) {
        return repo.findByCity(city);
    }

    public Optional<Customer> getCustomerById(Long id) {
        return repo.findById(id);
    }
}

---

7️⃣ Controller: Multiple Input Styles

@RestController
@RequestMapping("/api/v2/customers")
public class CustomerController {
    @Autowired private CustomerService service;

    // --- 1. POST with RequestBody
    @PostMapping
    public ResponseEntity<CustomerDTO> createCustomer(@RequestBody Customer customer) {
        Customer saved = service.createCustomer(customer);
        return ResponseEntity.status(HttpStatus.CREATED).body(new CustomerDTO(saved));
    }

    // --- 2. POST with RequestParam (Quick Submit Form)
    @PostMapping("/quick")
    public ResponseEntity<String> quickCreate(
        @RequestParam String name,
        @RequestParam String email
    ) {
        Customer c = new Customer();
        c.setName(name); c.setEmail(email);
        c.setCity("Unknown"); c.setAge(0);
        service.createCustomer(c);
        return ResponseEntity.ok("Customer created: " + name);
    }

    // --- 3. GET by ID with PathVariable
    @GetMapping("/{id}")
    public ResponseEntity<CustomerDTO> getById(@PathVariable Long id) {
        return service.getCustomerById(id)
            .map(c -> ResponseEntity.ok(new CustomerDTO(c)))
            .orElse(ResponseEntity.notFound().build());
    }

    // --- 4. GET by City with Query Param
    @GetMapping
    public ResponseEntity<List<CustomerDTO>> getByCity(@RequestParam String city) {
        List<Customer> customers = service.getCustomersByCity(city);
        List<CustomerDTO> dtos = customers.stream().map(CustomerDTO::new).toList();
        return ResponseEntity.ok(dtos);
    }
}

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8️⃣ Bonus: ApiResponse.java Utility Wrapper (optional)

public class ApiResponse<T> {
    private T data;
    private String message;
    private LocalDateTime timestamp = LocalDateTime.now();

    // constructor, getters, setters
}

---

🧪 Test Cases with Postman (Manually or Auto Test)

• POST /api/v2/customers
  Body:

  {
    "name": "Ravi",
    "email": "[email protected]",
    "city": "Bangalore",
    "age": 29
  }

• POST /api/v2/customers/quick?name=Mini&[email protected]

• GET /api/v2/customers/1

• GET /api/v2/customers?city=Bangalore

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💡 Learning Takeaways

• Use of @RequestBody, @RequestParam, @PathVariable
• Different use-cases → same result via alternate methods
• Clean code separation using DTO and layers
• Reusable APIs and future-proofing endpoint design