Multi-part Exercise: SmartCart: Build Your First Enterprise-Grade Product API

[akash-coded]

🧠 Exercise Title: "SmartCart: Build Your First Enterprise-Grade Product API"

🗂️ Objective:

Design and implement a Spring Boot REST API for managing a shopping cart's product catalog with full CRUD operations, H2 database, request validation, DTO-layer, logging, caching, Swagger, and unit tests.

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🧩 Step 0: Project Setup

🛠 Task:

• Go to https://start.spring.io/

• Add dependencies:

  • Spring Web
  • Spring Data JPA
  • H2 Database
  • Spring Boot DevTools
  • Lombok
  • Spring Boot Validation
  • Springdoc OpenAPI
  • Spring Cache (optional)
  • Spring Boot Test

📁 Expected Project Structure:

src/main/java/com/example/smartcart/
├── controller/
│   └── ProductController.java
├── dto/
│   └── ProductDTO.java
├── exception/
│   ├── GlobalExceptionHandler.java
│   └── ProductNotFoundException.java
├── model/
│   └── Product.java
├── repository/
│   └── ProductRepository.java
├── service/
│   ├── ProductService.java
│   └── impl/
│       └── ProductServiceImpl.java
└── SmartCartApplication.java

---

🧾 Step 1: Define the Model

🔧 Create Entity:
Product.java with fields:

• id: Long
• name: String
• description: String
• category: String
• price: double
• stockQty: int

📌 Annotate with @Entity, @Table, and @Id.

📘 Use Lombok to reduce boilerplate:

@Getter @Setter @NoArgsConstructor @AllArgsConstructor @ToString

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💡 Step 2: DTOs & Validation

🔍 Create ProductDTO.java with same fields (but without id for creation).

🎯 Add validation:

• @NotBlank, @Size, @Min, @NotNull, etc.

🛡 Example:

@NotBlank(message = "Product name cannot be blank")
@Size(min = 3, max = 50)
private String name;

---

🎯 Step 3: Repository Layer

🧱 Create ProductRepository.java

@Repository
public interface ProductRepository extends JpaRepository<Product, Long> {
    List<Product> findByCategoryIgnoreCase(String category);
}

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🔍 Step 4: Service Layer Interface & Impl

📌 Define ProductService interface:

List<ProductDTO> getAllProducts();
ProductDTO getProductById(Long id);
ProductDTO createProduct(ProductDTO dto);
ProductDTO updateProduct(Long id, ProductDTO dto);
void deleteProduct(Long id);
List<ProductDTO> getByCategory(String category);
double getInventoryValue(); // Total price * quantity

📌 Implement it in ProductServiceImpl.java

Use:

• ModelMapper for DTO ↔ Entity conversion (or manual mapping)
• Optional and custom exceptions
• Logging (Slf4j)
• Stream API to calculate inventory value

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🌐 Step 5: Controller Layer

🎮 Create ProductController.java

Map endpoints:

Method	Path	Description
GET	/api/products	Get all products
GET	/api/products/{id}	Get product by ID
POST	/api/products	Create new product
PUT	/api/products/{id}	Update product by ID
DELETE	/api/products/{id}	Delete product
GET	/api/products/category	Get products by category (query)
GET	/api/products/value	Get total inventory value

Use:

• @RequestParam, @PathVariable, @Valid
• @Operation from Swagger annotations

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🚨 Step 6: Error Handling

🛡 Add:

• ProductNotFoundException extends RuntimeException

• GlobalExceptionHandler with:

  • @ExceptionHandler
  • @ResponseStatus
  • Custom error structure

---

💾 Step 7: Seed Data

📁 Create schema.sql and data.sql

INSERT INTO product (id, name, description, category, price, stock_qty)
VALUES (1, 'iPhone', 'Smartphone', 'Electronics', 699.99, 10);

---

⚙️ Step 8: application.properties

server.port=8085

spring.datasource.url=jdbc:h2:mem:smartcart
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=
spring.h2.console.enabled=true

spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true
logging.level.org.springframework=INFO

---

📘 Step 9: Swagger + H2

• Swagger UI: http://localhost:8085/swagger-ui/index.html
• H2 Console: http://localhost:8085/h2-console

---

📦 Step 10: Add Caching (Optional)

In ProductServiceImpl:

@Cacheable("products")
public List<ProductDTO> getAllProducts() { ... }

@CacheEvict("products")
public ProductDTO createProduct(...) { ... }

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✅ Step 11: Add Unit Tests

• Use @WebMvcTest for controller testing
• Mock service layer with @MockBean
• Use MockMvc and test edge cases

---

🧪 Postman Requests to Test

✅ Create:

POST /api/products
{
  "name": "MacBook",
  "description": "Apple Laptop",
  "category": "Electronics",
  "price": 1200,
  "stockQty": 5
}

❌ Edge Case:

• Missing name
• Negative price
• Invalid category

---

💡 Bonus Challenges

• Add sorting by price or name (/api/products?sort=price)
• Implement pagination
• Introduce a Review entity and map it to Product (OneToMany)

[akash-coded]

Here’s your downloadable base Spring Boot project template:

📦 smartcart-api-template.zip

This template includes:

• Clean enterprise-style folder structure
• Pre-configured application.properties with H2 and logging
• Ready-to-use starter SmartCartApplication.java
• Setup instructions in README.md
• Placeholders for controller, service, model, repository, etc.

Use this as the starting point for your next exercise.

[akash-coded]

🧠 Exercise: Build SmartCart - A Mini E-Commerce REST API

🎯 Objective

You will build a feature-complete Spring Boot REST API for managing a product catalog. You will learn:

• Clean architecture (Controller → Service → Repository → Model → DTO)
• Validation, Exception Handling
• H2 DB config and data seeding
• Swagger / OpenAPI usage
• Java 8 Stream API
• String operations in an API context
• DTO to Entity mapping using ModelMapper
• Best coding practices and conventions

---

🛠️ STEP 1: Project Setup

⏳ 15 mins

1. Unzip and import the template project:
   smartcart-api-template.zip

2. Ensure the following dependencies exist in pom.xml:

   <dependencies>
       <dependency>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-starter-web</artifactId>
       </dependency>
       <dependency>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-starter-data-jpa</artifactId>
       </dependency>
       <dependency>
           <groupId>com.h2database</groupId>
           <artifactId>h2</artifactId>
       </dependency>
       <dependency>
           <groupId>org.springdoc</groupId>
           <artifactId>springdoc-openapi-ui</artifactId>
           <version>1.6.14</version>
       </dependency>
       <dependency>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-starter-validation</artifactId>
       </dependency>
       <dependency>
           <groupId>org.modelmapper</groupId>
           <artifactId>modelmapper</artifactId>
           <version>2.4.4</version>
       </dependency>
   </dependencies>

3. Run the app

   • Swagger UI: http://localhost:8085/swagger-ui/index.html
   • H2 Console: http://localhost:8085/h2-console

---

🧱 STEP 2: Define the Product Domain

⏳ 20 mins

🔹 Product.java (Entity)

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

    private String name;
    private double price;
    private String category;
}

🔹 ProductDTO.java (DTO)

@Data
public class ProductDTO {
    @NotBlank(message = "Name is mandatory")
    private String name;

    @Min(value = 1, message = "Price must be positive")
    private double price;

    private String category;
}

🔄 Map DTO → Entity using ModelMapper.

---

🗂️ STEP 3: Create Repository and Seed Data

⏳ 10 mins

🔹 ProductRepository.java

public interface ProductRepository extends JpaRepository<Product, Long> {
    List<Product> findByCategory(String category);
}

🔹 data.sql

INSERT INTO PRODUCT (name, price, category) VALUES ('Laptop', 75000, 'Electronics');
INSERT INTO PRODUCT (name, price, category) VALUES ('Shoes', 2500, 'Fashion');
INSERT INTO PRODUCT (name, price, category) VALUES ('Watch', 12000, 'Accessories');

---

🔧 STEP 4: Implement Service Layer with Two Variants

⏳ 30 mins

1. ProductService interface
2. ProductServiceImpl (traditional approach with loops)
3. ProductServiceStreamImpl (Java 8 Stream API)

🧪 Include operations:

• List all products
• Find by category
• Get all product names
• Get most expensive product
• Total price
• Filter by substring in product name (String API)
• Uppercase all product names

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🌐 STEP 5: Build Controller with Swagger Annotations

⏳ 20 mins

@RestController
@RequestMapping("/api/products")
@RequiredArgsConstructor
@Tag(name = "Product API", description = "Operations for product management")
public class ProductController {

    @Qualifier("streamService")
    private final ProductService productService;

    @Operation(summary = "List all products")
    @GetMapping
    public List<ProductDTO> getAllProducts() {
        return productService.getAllProducts()
                             .stream()
                             .map(p -> modelMapper.map(p, ProductDTO.class))
                             .collect(Collectors.toList());
    }

    @GetMapping("/expensive")
    public ProductDTO getMostExpensive() {
        return modelMapper.map(productService.getMostExpensiveProduct(), ProductDTO.class);
    }

    // Add: byCategory, byNameSubstring, totalPrice, etc.
}

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💡 STEP 6: Add Extras

⏳ 25 mins

• Add a custom exception for ProductNotFound
• Add a global exception handler (@ControllerAdvice)
• Enable @Cacheable for getAllProducts()
• Implement Pageable for large datasets

---

📫 STEP 7: Test with Postman

• GET /api/products
• GET /api/products?category=Electronics
• GET /api/products/names
• GET /api/products/total
• GET /api/products/expensive
• GET /api/products/search?substring=lap
• POST /api/products with invalid fields
• DELETE /api/products/100 (to trigger 404)

---

🧪 BONUS: Add Unit Tests

• Test ProductServiceStreamImpl
• Mock ProductRepository
• Validate DTO to Entity conversion
• Verify @ExceptionHandler works

[akash-coded]

✅ Here is your complete SmartCart exercise bundle with guidelines, starter project, and Postman setup:

📦 smartcart-exercise-bundle.zip

Inside you'll find:

• 🧾 README_SmartCart_Exercise.md – step-by-step instructions
• 🚀 Postman collection stub (SmartCart.postman_collection.json)
• 📁 Starter Spring Boot template (smartcart-api-template.zip from earlier)

[Sdey0907]

**

Task - SmartCart_ Product API _Sayan Dey_Completed

**

smartcart_Product_SpringBoot.zip

[prasetha21-max]

PRASETHA N
smartcart.zip