Inventory Management System

@RestController
@RequestMapping("/inventory")
public class InventoryController {
}

// 1. Product Entity
import jakarta.persistence.*;

@Entity
class Product {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

  private String name;
  private String category;
  private Integer quantity;
  private Double price;
}


// 2. Supplier Entity
@Entity
class Supplier {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

  private String name;
  private String contact;
}


// 3. Inventory Transaction Entity
@Entity
class InventoryTransaction {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

  private Long productId;
  private String type; // ADD / REMOVE
  private Integer quantity;
}


// 4. Repository Layer
import org.springframework.data.jpa.repository.JpaRepository;

interface ProductRepository extends JpaRepository<Product, Long> {}
interface SupplierRepository extends JpaRepository<Supplier, Long> {}
interface InventoryTransactionRepository extends JpaRepository<InventoryTransaction, Long> {}


// 5. Service Layer
import org.springframework.stereotype.Service;

@Service
class InventoryService {

  private final ProductRepository productRepo;
  private final SupplierRepository supplierRepo;
  private final InventoryTransactionRepository transactionRepo;

  public InventoryService(ProductRepository productRepo, SupplierRepository supplierRepo, InventoryTransactionRepository transactionRepo) {
    this.productRepo = productRepo;
    this.supplierRepo = supplierRepo;
    this.transactionRepo = transactionRepo;
  }

  public Product addStock(Long productId, int qty) {

    Product p = productRepo.findById(productId).orElseThrow();

    p.setQuantity(p.getQuantity() + qty);

    InventoryTransaction t = new InventoryTransaction();
    t.setProductId(productId);
    t.setType("ADD");
    t.setQuantity(qty);

    transactionRepo.save(t);
    return productRepo.save(p);
  }

  public Product removeStock(Long productId, int qty) {

    Product p = productRepo.findById(productId).orElseThrow();

    if (p.getQuantity() < qty) {
      throw new RuntimeException("Insufficient Stock");
    }

    p.setQuantity(p.getQuantity() - qty);

    InventoryTransaction t = new InventoryTransaction();
    t.setProductId(productId);
    t.setType("REMOVE");
    t.setQuantity(qty);

    transactionRepo.save(t);
    return productRepo.save(p);
  }
}


// 6. Controller Layer
import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/inventory")
class InventoryController {

  private final InventoryService service;

  public InventoryController(InventoryService service) {
    this.service = service;
  }

  @PostMapping("/add-stock/{id}")
  public Product addStock(@PathVariable Long id, @RequestParam int qty) {
    return service.addStock(id, qty);
  }

  @PostMapping("/remove-stock/{id}")
  public Product removeStock(@PathVariable Long id, @RequestParam int qty) {
    return service.removeStock(id, qty);
  }
}


// 7. application.properties
spring.datasource.url=jdbc:mysql://localhost:3306/inventory
spring.datasource.username=root
spring.datasource.password=root
spring.jpa.hibernate.ddl-auto=update


// Output:
// /inventory/add-stock -> Increase stock
// /inventory/remove-stock -> Decrease stock

• 1 System to track product stock.
• 2 Manages suppliers and warehouses.
• 3 Handles stock in/out operations.
• 4 Used in retail and logistics.

• 1 Add stock
• 2 Remove stock
• 3 Track inventory
• 4 Manage suppliers

• 1 Product added to inventory
• 2 Stock updated on sales
• 3 Transactions recorded
• 4 Reports generated

• 1 Avoid stock shortages
• 2 Improve business efficiency
• 3 Real-time tracking
• 4 Reduce manual errors

• 1 Used in retail businesses.
• 2 Used in warehouse systems.
• 3 Used in manufacturing companies.
• 4 Used in supply chain management.
• 5 SaaS products use Inventory Management System using Spring Boot in services, dashboards, background jobs, and API workflows.
• 6 ERP and banking systems apply Inventory Management System using Spring Boot with validation, logging, review, and rollback plans.
• 7 E-commerce and healthcare platforms use Inventory Management System using Spring Boot carefully because reliability and data correctness matter.

• 1 A Java program first evaluates the surrounding context, then applies the Inventory Management System using Spring Boot rules to the current data.
• 2 The important mental model is input, transformation, result, and failure path.
• 3 In production, the same flow usually sits inside a larger layer such as a controller, service, repository, job, or UI component.

• 1 Choose the simplest implementation first, then measure real workloads.
• 2 Watch for repeated work inside loops, unnecessary allocations, and slow I/O in hot paths.
• 3 Prefer clear data structures and stable APIs before micro-optimizing syntax.

• 1 Treat external input as untrusted until it is validated.
• 2 Avoid hardcoded secrets and never print sensitive values in examples or logs.
• 3 Use established libraries for authentication, encryption, parsing, and database access.

• 1 Not validating stock levels.
• 2 Missing transaction logs.
• 3 Poor supplier management.
• 4 No concurrency handling in stock updates.
• 5 Skipping the small working example before adding framework code.
• 6 Ignoring null, empty, duplicate, and boundary inputs.
• 7 Mixing business logic, input handling, and output formatting in one place.
• 8 Using broad error handling that hides the real failure.
• 9 Forgetting to test the behavior after refactoring.
• 10 Adding clever code that future maintainers will struggle to read.

• 1 Use database locking for stock updates.
• 2 Maintain inventory audit logs.
• 3 Use microservices for scalability.
• 4 Implement real-time stock tracking.
• 5 Start with clear requirements and one minimal working example.
• 6 Use meaningful names that explain business intent.
• 7 Keep examples small enough to debug line by line.
• 8 Validate input at every trust boundary.
• 9 Handle errors explicitly and preserve useful context.
• 10 Prefer simple control flow over deeply nested logic.
• 11 Separate domain logic from I/O and framework code.
• 12 Write tests for normal, boundary, and failure cases.
• 13 Review security assumptions before production use.
• 14 Measure performance before optimizing.
• 15 Document non-obvious decisions close to the code or in project notes.
• 16 Use official documentation when behavior is version-specific.
• 17 Keep dependencies current and remove unused code.
• 18 Avoid hardcoded secrets, credentials, and environment-specific paths.
• 19 Log operational events without exposing sensitive data.
• 20 Design examples so learners can safely modify and rerun them.

• 1 Beginner: rewrite the example with different names and values.
• 2 Intermediate: add validation and handle one expected failure case.
• 3 Advanced: place Inventory Management System using Spring Boot inside a small service-style design with tests.

• 1 Build a small Java console feature that demonstrates Inventory Management System using Spring Boot.
• 2 Accept input, process it with the concept, print a clear result, and handle invalid input.
• 3 Add a README note explaining the design choice and two edge cases you tested.

• 1 If the program does not compile, check spelling, imports, braces, and file/class names first.
• 2 If output is unexpected, print intermediate values and verify each branch of the logic.
• 3 If the design feels complex, reduce it to the smallest working example and add pieces back one at a time.

• 1 Practice Inventory Management System using Spring Boot with a second example from a business domain such as inventory, payroll, banking, or e-commerce.
• 2 Review related Java topics that cover data flow, error handling, testing, and clean design.
• 3 Compare your solution with official documentation and simplify anything you cannot explain clearly.