@Target( { METHOD, FIELD, ANNOTATION_TYPE })
@Retention(RUNTIME)
@Constraint(validatedBy = ByteLengthValidator.class)// 使用@Constraint指定注解校驗實現(xiàn)類，這是一個限制型注解，只能使用指定的實現(xiàn)類
@Documented
public @interface ByteLength {
    int min() default 0; 
    int max() default 2147483647; 
    String charsetName() default "GBK"; 
    String message() default "的長度只能在{min}和{max}之間"; 
    Class<?>[] groups() default {}; 
    Class<? extends Payload>[] payload() default {};
}

public class ByteLengthValidator implements ConstraintValidator<ByteLength, String>{   // 實現(xiàn)ConstraintValidator 
 int min;
 int max;
        String charsetName;
 
 @Override
 public void initialize(ByteLength constraintAnnotation) {
  this.min = constraintAnnotation.min();
  this.max = constraintAnnotation.max();
        this.charsetName = constraintAnnotation.charsetName();
 }
 
 @Override
 public boolean isValid(String value, ConstraintValidatorContext context) {   // 實現(xiàn)校驗規(guī)則
        if (null == value) {
            return min <= 0;
        } 
        try {
            int length = value.getBytes(charsetName).length;
            return length >= min && length <= max;
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
            return false;
        }
 }
}