校验 Validation — JSR-303 / JSR-380 Bean Validation

public void createProduct(ProductForm form) {
    if (form.getName() == null || form.getName().isBlank()) {
        throw new IllegalArgumentException("商品名称不能为空");
    }
    if (form.getPrice() == null || form.getPrice() <= 0) {
        throw new IllegalArgumentException("价格必须大于0");
    }
    // ... 20 个字段要校验，代码爆炸
}

public class ProductForm {

    @NotBlank(message = "商品名称不能为空")
    @Size(max = 100, message = "商品名称最多 100 个字符")
    private String name;

    @NotNull(message = "价格不能为空")
    @Positive(message = "价格必须大于 0")
    @Digits(integer = 8, fraction = 2, message = "价格格式错误，最多 8 位整数 2 位小数")
    private BigDecimal price;

    @NotNull(message = "库存不能为空")
    @Min(value = 0, message = "库存不能为负数")
    @Max(value = 999999, message = "库存超出上限")
    private Integer stock;

    @NotBlank(message = "商品分类不能为空")
    private String category;

    @Email(message = "负责人邮箱格式不正确")
    private String managerEmail;

    @Pattern(regexp = "^FX-[0-9]+$", message = "商品编码格式必须为 FX-数字")
    private String productCode;

    // getters / setters...
}

@RestController
@RequestMapping("/api/products")
public class ProductController {

    @PostMapping
    public ResponseEntity<Product> createProduct(
            @RequestBody @Valid ProductForm form) {
        // 如果校验失败，Spring 自动抛 MethodArgumentNotValidException
        // 由 @ControllerAdvice 统一处理返回 400
        Product product = productService.create(form);
        return ResponseEntity.status(HttpStatus.CREATED).body(product);
    }
}

@RestControllerAdvice
public class ValidationExceptionHandler {

    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity<Map<String, Object>> handleValidationErrors(
            MethodArgumentNotValidException ex) {

        List<String> errors = ex.getBindingResult()
            .getFieldErrors()
            .stream()
            .map(error -> error.getField() + ": " + error.getDefaultMessage())
            .collect(Collectors.toList());

        Map<String, Object> body = Map.of(
            "error", "VALIDATION_FAILED",
            "message", "请求参数校验失败",
            "details", errors
        );

        return ResponseEntity.badRequest().body(body);
    }
}

public interface CreateGroup {}   // 创建时校验
public interface UpdateGroup {}   // 更新时校验

public class ProductForm {

    @NotBlank(groups = CreateGroup.class)
    private String name;

    @NotNull(groups = {CreateGroup.class, UpdateGroup.class})
    @Positive
    private BigDecimal price;

    // 更新时允许不传库存（不修改）
    @NotNull(groups = CreateGroup.class)
    @Min(0)
    private Integer stock;
}

@PostMapping
public Product create(@RequestBody @Validated(CreateGroup.class) ProductForm form) {
    // 创建时校验 name、price、stock
}

@PutMapping("/{id}")
public Product update(@RequestBody @Validated(UpdateGroup.class) ProductForm form) {
    // 更新时只强制校验 price
}

@Target({FIELD})
@Retention(RUNTIME)
@Constraint(validatedBy = NoSensitiveWordValidator.class)
public @interface NoSensitiveWord {
    String message() default "包含敏感词汇";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}

public class NoSensitiveWordValidator implements ConstraintValidator<NoSensitiveWord, String> {

    private static final List<String> SENSITIVE_WORDS = List.of("暴力", "色情", "赌博");

    @Override
    public boolean isValid(String value, ConstraintValidatorContext context) {
        if (value == null || value.isBlank()) {
            return true;  // @NotBlank 负责判空
        }
        return SENSITIVE_WORDS.stream().noneMatch(value::contains);
    }
}

public class ProductForm {
    @NotBlank
    @NoSensitiveWord(message = "商品名称包含违规内容")
    private String name;
}