第二章练习答案

练习 1：完整 CRUD REST API

@RestController
@RequestMapping("/api/products")
public class ProductController {
    
    @Autowired
    private ProductService productService;
    
    @GetMapping
    public ResponseEntity<List<Product>> getAllProducts(
        @RequestParam(defaultValue = "0") int page,
        @RequestParam(defaultValue = "10") int size
    ) {
        Page<Product> productPage = productService.findAll(PageRequest.of(page, size));
        return ResponseEntity.ok(productPage.getContent());
    }
    
    @GetMapping("/{id}")
    public ResponseEntity<Product> getProduct(@PathVariable Long id) {
        return productService.findById(id)
            .map(ResponseEntity::ok)
            .orElse(ResponseEntity.notFound().build());
    }
    
    @PostMapping
    public ResponseEntity<Product> createProduct(@Valid @RequestBody Product product) {
        Product saved = productService.save(product);
        return ResponseEntity
            .created(URI.create("/api/products/" + saved.getId()))
            .body(saved);
    }
    
    @PutMapping("/{id}")
    public ResponseEntity<Product> updateProduct(
        @PathVariable Long id,
        @Valid @RequestBody Product product
    ) {
        if (!productService.exists(id)) {
            return ResponseEntity.notFound().build();
        }
        product.setId(id);
        return ResponseEntity.ok(productService.save(product));
    }
    
    @DeleteMapping("/{id}")
    public ResponseEntity<Void> deleteProduct(@PathVariable Long id) {
        if (!productService.exists(id)) {
            return ResponseEntity.notFound().build();
        }
        productService.delete(id);
        return ResponseEntity.noContent().build();
    }
}

练习 2：全局异常处理

@ControllerAdvice
public class GlobalExceptionHandler {
    
    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<ErrorResponse> handleResourceNotFound(
        ResourceNotFoundException ex,
        WebRequest request
    ) {
        ErrorResponse error = new ErrorResponse(
            HttpStatus.NOT_FOUND.value(),
            ex.getMessage(),
            request.getDescription(false),
            LocalDateTime.now()
        );
        return ResponseEntity.status(HttpStatus.NOT_FOUND).body(error);
    }
    
    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity<Map<String, String>> handleValidationExceptions(
        MethodArgumentNotValidException ex
    ) {
        Map<String, String> errors = new HashMap<>();
        ex.getBindingResult().getAllErrors().forEach(error -> {
            String fieldName = ((FieldError) error).getField();
            String errorMessage = error.getDefaultMessage();
            errors.put(fieldName, errorMessage);
        });
        return ResponseEntity.badRequest().body(errors);
    }
    
    @ExceptionHandler(Exception.class)
    public ResponseEntity<ErrorResponse> handleGlobalException(
        Exception ex,
        WebRequest request
    ) {
        ErrorResponse error = new ErrorResponse(
            HttpStatus.INTERNAL_SERVER_ERROR.value(),
            "An unexpected error occurred",
            request.getDescription(false),
            LocalDateTime.now()
        );
        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body(error);
    }
}

@Data
@AllArgsConstructor
public class ErrorResponse {
    private int status;
    private String message;
    private String path;
    private LocalDateTime timestamp;
}

练习 3：数据验证

@Entity
@Table(name = "products")
public class Product {
    
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    @NotBlank(message = "Product name is required")
    @Size(min = 3, max = 100, message = "Name must be between 3 and 100 characters")
    private String name;
    
    @NotNull(message = "Price is required")
    @DecimalMin(value = "0.01", message = "Price must be greater than 0")
    @DecimalMax(value = "999999.99", message = "Price must be less than 1,000,000")
    private BigDecimal price;
    
    @Min(value = 0, message = "Stock cannot be negative")
    private Integer stock;
    
    @Email(message = "Supplier email must be valid")
    private String supplierEmail;
    
    @Pattern(regexp = "^[A-Z]{2}\\d{6}$", message = "SKU must be 2 letters followed by 6 digits")
    private String sku;
    
    // getters and setters
}

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