// 需要手動校驗(yàn)每個字段，代碼冗余且易出錯
public String register(User user) {
    // 手動校驗(yàn)每個字段
    if (user.getEmail() == null || !isValidEmail(user.getEmail())) {
        throw new IllegalArgumentException("郵箱格式錯誤");
    }
    if (user.getPassword().length() < 8) {
        throw new IllegalArgumentException("密碼長度需≥8位");
    }
    // 校驗(yàn)邏輯與業(yè)務(wù)代碼耦合，難以復(fù)用
}

public class User {
    @Email(message = "郵箱格式不合法")  // 一行注解替代復(fù)雜校驗(yàn)
    private String email;
    
    @Size(min = 8, message = "密碼長度需≥8位")
    private String password;
}

@PostMapping("/register")
public String register(@Valid @RequestBody User user) { 
    // 校驗(yàn)邏輯由框架自動處理
    return "success";
}

<!-- pom.xml 必須依賴 -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-validation</artifactId>
</dependency>

public class User {
    @NotNull(message = "用戶名不能為空")
    private String name;
    
    @Min(value = 18, message = "年齡必須≥18歲")
    private Integer age;
}

@PostMapping("/users")
public String createUser(@Valid @RequestBody User user) { // 觸發(fā)校驗(yàn)
    return "success";
}

@RestControllerAdvice
public class GlobalExceptionHandler {
    
    // 處理@Valid/@Validated拋出的校驗(yàn)異常
    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity<Map<String, String>> handleValidationException(MethodArgumentNotValidException ex) {
        Map<String, String> errors = new HashMap<>();
        ex.getBindingResult().getFieldErrors().forEach(error -> 
            errors.put(error.getField(), error.getDefaultMessage()));
        return ResponseEntity.badRequest().body(errors);
    }
}

// 分組接口定義
public interface CreateGroup {} 
public interface UpdateGroup {}

public class User {
    @NotBlank(groups = CreateGroup.class)
    private String name;
    
    @NotNull(groups = {CreateGroup.class, UpdateGroup.class})
    private Integer age;
}

// 使用分組校驗(yàn)
@PostMapping("/users")
public String createUser(@Validated(CreateGroup.class) @RequestBody User user) {
    return "success";
}

// 自定義手機(jī)號校驗(yàn)注解
@Documented
@Constraint(validatedBy = PhoneValidator.class)
@Target({FIELD, PARAMETER})
@Retention(RUNTIME)
public @interface Phone {
    String message() default "手機(jī)號格式不合法";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}

// 校驗(yàn)邏輯實(shí)現(xiàn)
public class PhoneValidator implements ConstraintValidator<Phone, String> {
    private static final Pattern PHONE_PATTERN = Pattern.compile("^1[3-9]\\d{9}$");
    
    @Override
    public boolean isValid(String value, ConstraintValidatorContext context) {
        return value != null && PHONE_PATTERN.matcher(value).matches();
    }
}

// 動態(tài)分組校驗(yàn)（根據(jù)請求參數(shù)決定校驗(yàn)組）
@Validated
@RestController
public class UserController {
    
    @PostMapping("/users")
    public String createUser(
        @RequestParam String type,
        @Validated({Default.class, type.equals("vip") ? VipGroup.class : Default.class}) 
        @RequestBody User user
    ) {
        return "success";
    }
}

// 嵌套校驗(yàn)示例
public class Order {
    @Valid  // 必須顯式添加
    private User user;
}

// 分組校驗(yàn)示例
@Validated(UpdateGroup.class)
public void updateUser(@RequestBody User user) {}