Response
Here's the complete implementation, following the house conventions (constructor injection, domain exceptions mapped by a `@RestControllerAdvice`, `ApiResponse` envelope).
```java
package com.acme.billing;
public enum InvoiceStatus {
UNPAID,
PAID,
CANCELLED
}
```
```java
package com.acme.billing;
import java.util.Optional;
public interface InvoiceRepository {
Optional<Invoice> findById(long id);
}
```
```java
package com.acme.billing;
public interface Invoice {
long customerId();
InvoiceStatus status();
void markCancelled();
}
```
```java
package com.acme.billing;
public class InvoiceNotFoundException extends RuntimeException {
public InvoiceNotFoundException(long invoiceId) {
super("Invoice " + invoiceId + " was not found");
}
}
```
```java
package com.acme.billing;
public class InvoiceAccessDeniedException extends RuntimeException {
public InvoiceAccessDeniedException(long invoiceId) {
super("Invoice " + invoiceId + " does not belong to the current customer");
}
}
```
```java
package com.acme.billing;
public class InvoiceNotCancellableException extends RuntimeException {
public InvoiceNotCancellableException(long invoiceId, InvoiceStatus status) {
super("Invoice " + invoiceId + " cannot be cancelled because its status is " + status);
}
}
```
```java
package com.acme.billing;
public class InvoiceService {
private final InvoiceRepository invoiceRepository;
public InvoiceService(InvoiceRepository invoiceRepository) {
this.invoiceRepository = invoiceRepository;
}
public void cancelInvoice(long invoiceId, long customerId) {
Invoice invoice = invoiceRepository.findById(invoiceId)
.orElseThrow(() -> new InvoiceNotFoundException(invoiceId));
if (invoice.customerId() != customerId) {
throw new InvoiceAccessDeniedException(invoiceId);
}
if (invoice.status() != InvoiceStatus.UNPAID) {
throw new InvoiceNotCancellableException(invoiceId, invoice.status());
}
invoice.markCancelled();
}
}
```
```java
package com.acme.billing;
public record ApiResponse<T>(boolean success, T data, ApiError error) {
public static <T> ApiResponse<T> ok(T data) {
return new ApiResponse<>(true, data, null);
}
public static <T> ApiResponse<T> error(String code, String message) {
return new ApiResponse<>(false, null, new ApiError(code, message));
}
public record ApiError(String code, String message) {}
}
```
```java
package com.acme.billing;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.RestControllerAdvice;
@RestControllerAdvice
public class InvoiceExceptionHandler {
@ExceptionHandler(InvoiceNotFoundException.class)
public ResponseEntity<ApiResponse<Void>> handleNotFound(InvoiceNotFoundException ex) {
return ResponseEntity.status(HttpStatus.NOT_FOUND)
.body(ApiResponse.error("INVOICE_NOT_FOUND", ex.getMessage()));
}
@ExceptionHandler(InvoiceAccessDeniedException.class)
public ResponseEntity<ApiResponse<Void>> handleAccessDenied(InvoiceAccessDeniedException ex) {
return ResponseEntity.status(HttpStatus.FORBIDDEN)
.body(ApiResponse.error("INVOICE_ACCESS_DENIED", ex.getMessage()));
}
@ExceptionHandler(InvoiceNotCancellableException.class)
public ResponseEntity<ApiResponse<Void>> handleNotCancellable(InvoiceNotCancellableException ex) {
return ResponseEntity.status(HttpStatus.CONFLICT)
.body(ApiResponse.error("INVOICE_NOT_CANCELLABLE", ex.getMessage()));
}
}
```
```java
package com.acme.billing;
import org.springframework.security.core.annotation.AuthenticationPrincipal;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
@RequestMapping("/api/invoices")
public class InvoiceController {
private final InvoiceService invoiceService;
public InvoiceController(InvoiceService invoiceService) {
this.invoiceService = invoiceService;
}
@PostMapping("/{invoiceId}/cancel")
public ApiResponse<Void> cancel(@PathVariable long invoiceId,
@AuthenticationPrincipal CustomerPrincipal principal) {
invoiceService.cancelInvoice(invoiceId, principal.customerId());
return ApiResponse.ok(null);
}
}
```
Note: `InvoiceStatus`, `Invoice`/`InvoiceRepository` signatures, and `CustomerPrincipal` (an `@AuthenticationPrincipal` exposing `customerId()`) are assumed to already exist in your codebase in roughly this shape — only `InvoiceService`, the three domain exceptions, `ApiResponse`, and `InvoiceExceptionHandler` are the actual new pieces; adjust the controller's principal type to whatever your security config already produces.
**Convention decisions applied:** constructor injection (no field injection/Lombok) in `InvoiceService`/`InvoiceController`; ownership and status checks live in the service as domain exceptions, with a `@RestControllerAdvice` translating them to `ApiResponse.error(...)` (404/403/409) so the controller stays thin and does no try/catch.