public interface ConstraintValidator<A extends Annotation, T> {
    void initialize(A constraintAnnotation);
    boolean isValid(T value, ConstraintValidatorContext context);
}

import javax.validation.Constraint;
import javax.validation.Payload;
import java.lang.annotation.*;

@Documented
@Constraint(validatedBy = LengthValidator.class) // 關(guān)聯(lián)驗(yàn)證器
@Target({ElementType.FIELD}) // 作用于字段
@Retention(RetentionPolicy.RUNTIME)
public @interface ValidLength {
    String message() default "Invalid length"; // 默認(rèn)錯(cuò)誤信息
    int min(); // 最小長度
    int max(); // 最大長度
    Class<?>[] groups() default {}; // 分組校驗(yàn)
    Class<? extends Payload>[] payload() default {};
}

import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;

public class LengthValidator implements ConstraintValidator<ValidLength, String> {
    private int min;
    private int max;

    @Override
    public void initialize(ValidLength constraintAnnotation) {
        this.min = constraintAnnotation.min();
        this.max = constraintAnnotation.max();
    }

    @Override
    public boolean isValid(String value, ConstraintValidatorContext context) {
        if (value == null || (value.length() >= min && value.length() <= max)) {
            return true;
        }

        // 禁用默認(rèn)錯(cuò)誤信息
        context.disableDefaultConstraintViolation();

        // 動(dòng)態(tài)構(gòu)建錯(cuò)誤信息
        String message = String.format("The length of '%s' must be between %d and %d.", value, min, max);
        context.buildConstraintViolationWithTemplate(message).addConstraintViolation();

        return false;
    }
}

public class User {
    @ValidLength(min = 6, max = 20, message = "Username length must be 6~20")
    private String username;
}

@RestController
public class UserController {
    @PostMapping("/user")
    public String createUser(@RequestBody @Valid User user) {
        return "User created successfully!";
    }
}

@Configuration
public class ValidationConfig {
    @Bean
    public MethodValidationPostProcessor methodValidationPostProcessor() {
        return new MethodValidationPostProcessor();
    }
}

@Override
public boolean isValid(String value, ConstraintValidatorContext context) {
    if (value == null || value.length() >= min && value.length() <= max) {
        return true;
    }

    context.disableDefaultConstraintViolation();
    String message = String.format("The length of '%s' must be between %d and %d.", value, min, max);
    context.buildConstraintViolationWithTemplate(message).addConstraintViolation();

    return false;
}

public interface RegistrationGroup {}
public interface LoginGroup {}

@ValidLength(min = 6, max = 20, groups = RegistrationGroup.class)
private String username;

Set<ConstraintViolation<User>> violations = validator.validate(user, RegistrationGroup.class);

# messages_en.properties
valid.length.message=The length of '{0}' must be between {1} and {2}.

# messages_zh.properties
valid.length.message=字段 '{0}' 的長度必須介于 {1} 和 {2} 之間。

String message = "{valid.length.message}";
context.buildConstraintViolationWithTemplate(message).addConstraintViolation();

@Constraint(validatedBy = EmailValidator.class)
@Target({ ElementType.FIELD })
@Retention(RetentionPolicy.RUNTIME)
public @interface ValidEmail {
    String message() default "Invalid email format";
    Class<?>[] groups() default {};
}

public class EmailValidator implements ConstraintValidator<ValidEmail, String> {
    @Override
    public boolean isValid(String email, ConstraintValidatorContext context) {
        if (email == null) return true; // 允許空值
        return email.matches("^[A-Za-z0-9+_.-]+@(.+)$");
    }
}

public class UniqueUsernameValidator implements ConstraintValidator<UniqueUsername, String> {
    @Autowired
    private UserRepository userRepository;

    @Override
    public boolean isValid(String username, ConstraintValidatorContext context) {
        return userRepository.findByUsername(username) == null;
    }
}

<dependency>
    <groupId>org.hibernate.validator</groupId>
    <artifactId>hibernate-validator</artifactId>
</dependency>

@ControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(ConstraintViolationException.class)
    public ResponseEntity<String> handleValidationExceptions(ConstraintViolationException ex) {
        StringBuilder sb = new StringBuilder();
        for (ConstraintViolation<?> violation : ex.getConstraintViolations()) {
            sb.append(violation.getMessage()).append("\n");
        }
        return ResponseEntity.badRequest().body(sb.toString());
    }
}

@GroupSequence({FirstGroup.class, SecondGroup.class})
public interface ValidationSequence {}